WorldWideScience

Sample records for mode-locked pulse train

  1. Intracavity coherent interaction of mode-locked pulse train with resonant medium

    Science.gov (United States)

    Masuda, Koji

    Resonant interactions of a mode-locked pulse train with intracavity samples, namely rubidium-87 (Rb-87) vapor and Fabry-Perot etalon, placed inside a laser cavity are studied in the light of developing ultra-sensitive laser sensors to measure a small magnetic field and a minute change of index of refraction of a sample material, respectively. A Rb-87 vapor provides an opportunity for a compact high-sensitivity atomic magnetometer due to its accessibility by the standard laser sources and to the large ensemble magnetization. By employing the ultra-sensitive interferometric technique utilizing the intracavity properties of a mode-locked laser, the performance of the Rb-87 magnetometer can be further improved. The fundamental properties of coherent interaction between a mode-locked pulse train and a Rb-87 vapor are studied in numerical calculations of 33 density matrix equations and the reduced wave equation, which are then examined in experiments. In particular, a coherent dark-state is created by the pulse train and is further enhanced by means of spectral shaping or polarization modulation of the excitation pulse train. Experiments performed inside a laser cavity show that the atomic coherence is still preserved due to the coherent nature of interaction between the Rb-87 vapor and the ultrashort pulses occurred within a short time scale compared to the atomic relaxation times, which results in nonlinear propagation of the pulses as well as an observation of the dark-line resonance inside the laser cavity. A Fabry-Perot etalon is a type of optical cavity and serves as a tuning element of the frequency of cw-lasers. By inserting a Fabry-Perot etalon inside a mode-locked laser, the cavity resonance modes are modied due to a coupling between the two cavities, which leads to unique temporal and spectral characteristics of the resultant pulse train and its frequency comb. Both the temporal and spectral properties of the pulse train are studied in detail in experiments as

  2. Properties of the pulse train generated by repetition-rate-doubling rational-harmonic actively mode-locked Er-doped fiber lasers.

    Science.gov (United States)

    Kiyan, R; Deparis, O; Pottiez, O; Mégret, P; Blondel, M

    2000-10-01

    We demonstrate for the first time to our knowledge, experimentally and theoretically, that the pulse-to-pulse amplitude fluctuations that occur in pulse trains generated by actively mode-locked Er-doped fiber lasers in a repetition-rate-doubling rational-harmonic mode-locking regime are completely eliminated when the modulation frequency is properly tuned. Irregularity of the pulse position in the train was found to be the only drawback of this regime. One could reduce the irregularity to a value acceptable for applications by increasing the bandwidth of the optical filter installed in the laser cavity.

  3. Ultralow-jitter passive timing stabilization of a mode-locked Er-doped fiber laser by injection of an optical pulse train.

    Science.gov (United States)

    Yoshitomi, Dai; Kobayashi, Yohei; Kakehata, Masayuki; Takada, Hideyuki; Torizuka, Kenji; Onuma, Taketo; Yokoi, Hideki; Sekiguchi, Takuro; Nakamura, Shinki

    2006-11-15

    The pulse timing of a mode-locked Er-doped fiber laser was stabilized to a reference pulse train from a Cr:forsterite mode-locked laser by all-optical passive synchronization scheme. The reference pulses were injected into a ring cavity of the fiber laser by using a 1.3-1.5 mum wavelength-division multiplexer. The spectral shift induced by cross-phase modulation between copropagating two-color pulses realizes self-synchronization due to intracavity group-delay dispersion. The rms integration of timing jitter between the fiber laser pulse and the reference pulse was 3.7 fs in a Fourier frequency range from 1 Hz to 100 kHz.

  4. Gigahertz repetition rate, sub-femtosecond timing jitter optical pulse train directly generated from a mode-locked Yb:KYW laser.

    Science.gov (United States)

    Yang, Heewon; Kim, Hyoji; Shin, Junho; Kim, Chur; Choi, Sun Young; Kim, Guang-Hoon; Rotermund, Fabian; Kim, Jungwon

    2014-01-01

    We show that a 1.13 GHz repetition rate optical pulse train with 0.70 fs high-frequency timing jitter (integration bandwidth of 17.5 kHz-10 MHz, where the measurement instrument-limited noise floor contributes 0.41 fs in 10 MHz bandwidth) can be directly generated from a free-running, single-mode diode-pumped Yb:KYW laser mode-locked by single-wall carbon nanotube-coated mirrors. To our knowledge, this is the lowest-timing-jitter optical pulse train with gigahertz repetition rate ever measured. If this pulse train is used for direct sampling of 565 MHz signals (Nyquist frequency of the pulse train), the jitter level demonstrated would correspond to the projected effective-number-of-bit of 17.8, which is much higher than the thermal noise limit of 50 Ω load resistance (~14 bits).

  5. High-repetition-rate ultrashort pulsed fiber ring laser using hybrid mode locking.

    Science.gov (United States)

    Zhang, Xiang; Hu, Hongyu; Li, Wenbo; Dutta, Niloy K

    2016-10-01

    We propose and demonstrate a hybrid mode-locked erbium-doped fiber ring laser by combining the rational harmonic mode-locking technique and passive mode locking based on nonlinear polarization rotation in a highly nonlinear photonic crystal fiber. By carefully adjusting the modulation frequency and the polarization controllers in the cavity, a 30 GHz pulse train with improved stability and narrower pulse width is generated. The pulse width at 30 GHz using rational harmonic mode locking alone is 5.8 ps. This hybrid scheme narrows the pulse width to 1.9 ps at the repetition rate of 30 GHz. Numerical simulations are carried out that show good agreement with the experimental results.

  6. Pulse properties of external cavity mode locked semiconductor lasers

    DEFF Research Database (Denmark)

    Mulet, Josep; Kroh, Marcel; Mørk, Jesper

    2006-01-01

    The performance of an external-cavity mode-locked semiconductor laser is investigated both theoretically and experimentally. The optimization analysis focuses on the regimes of stable mode locking and the generation of sub-picosecond optical pulses. We demonstrate stable output pulses down to one...... picosecond duration with more than 30 dB trailing pulse suppression. The limiting factors to the device performance are investigated on the basis of a fully-distributed time-domain model.We find that ultrafast gain dynamics effectively reduce the pulse-shaping strength and inhibit the generation...

  7. Generation of a 64-GHz, 3.3-ps transform-limited pulse train from a fiber laser employing higher-order frequency-modulated mode locking.

    Science.gov (United States)

    Abedin, K S; Onodera, N; Hyodo, M

    1999-11-15

    We demonstrate the generation of optical pulses at a repetition rate of 64 GHz directly from a frequency-modulated (FM) mode-locked fiber laser. This is achieved by phase modulation at 16 GHz and by initiating of higher-order FM mode locking by use of an intracavity Fabry-Perot filter with a free spectral range of 64 GHz. This process yielded transform-limited pulses with a width of 3.3 ps. We investigated the operating characteristics of the laser and compared them with the characteristics that were predicted theoretically.

  8. Modelling colliding-pulse mode-locked semiconductor lasers

    DEFF Research Database (Denmark)

    Bischoff, Svend

    or to determine the optimum operation conditions. The purpose of this thesis is to elucidate some of the physics of interest in the field of semiconductor laser modelling, semiconductor optics and fiber optics. To be more specific we will investigate: The Colliding-Pulse Mode-Locked (CPM) Quantum Well (QW) laser...

  9. Chirp of monolithic colliding pulse mode-locked diode lasers

    DEFF Research Database (Denmark)

    Hofmann, M.; Bischoff, S.; Franck, Thorkild

    1997-01-01

    Spectrally resolved streak camera measurements of picosecond pulses emitted by hybridly colliding pulse mode-locked (CPM) laser diodes are presented in this letter. Depending on the modulation frequency both blue-chirped (upchirped) and red-chirped (downchirped) pulses can be observed. The two...... different regimes and the transition between them are characterized experimentally and the behavior is explained on the basis of our model for the CPM laser dynamics. (C) 1997 American Institute of Physics....

  10. Flat pulse-amplitude rational-harmonic-mode-locking fiber lasers with GHz pulse repetition rates

    Science.gov (United States)

    Wang, Tianhe; Yang, Tianxin; Jia, Dongfang; Wang, Zhaoying; Sang, Mei; Bai, Neng; Li, Guifang

    2013-03-01

    Rational harmonic mode locking (RHML) in an active mode-locked fiber laser can increase the output pulse repetition rate a number of times the modulation frequency of an optical modulator in a cavity when driven by gigahertz (GHz) RF. The amplitudes of the output optical pulse train in a high order RHML operation are not equalized and flat due to the GHz RF drive signals. A modified RHML technique using standard instrumentation that generates 1 GHz electrical square wave signals to accomplish up to 6th order RHML in fiber lasers is presented for improving the flatness of the amplitudes of the output optical pulse train at the pulse repetition rate of up to 12 GHz.

  11. Mode-Locking in Broad-Area Semiconductor Lasers Enhanced by Picosecond-Pulse Injection

    OpenAIRE

    Kaiser, J; Fischer, I; Elsasser, W; Gehrig, E; Hess, O

    2004-01-01

    We present combined experimental and theoretical investigations of the picosecond emission dynamics of broad-area semiconductor lasers (BALs). We enhance the weak longitudinal self-mode-locking that is inherent to BALs by injecting a single optical 50-ps pulse, which triggers the output of a distinct regular train of 13-ps pulses. Modeling based on multimode Maxwell-Bloch equations illustrates how the dynamic interaction of the injected pulse with the internal laser field efficiently couples ...

  12. Modeling and characterization of pulse shape and pulse train dynamics in two-section passively mode-locked quantum dot lasers

    Science.gov (United States)

    Raghunathan, R.; Mee, J. K.; Crowley, M. T.; Grillot, F.; Kovanis, V.; Lester, L. F.

    2013-03-01

    A nonlinear delay differential equation model for passive mode-locking in semiconductor lasers, seeded with parameters extracted from the gain and loss spectra of a quantum dot laser, is employed to simulate and study the dynamical regimes of mode-locked operation of the device. The model parameter ranges corresponding to these regimes are then mapped to externally-controllable parameters such as gain current and absorber bias voltage. Using this approach, a map indicating the approximate regions corresponding to fundamental and harmonically mode locked operation is constructed as a function of gain current and absorber bias voltage. This is shown to be a highly useful method of getting a sense of the highest repetition rates achievable in principle with a simple, two-section device, and provides a guideline toward achieving higher repetition rates by simply adjusting external biasing conditions instantaneously while the device is in operation, as opposed to re-engineering the device with additional passive or saturable absorber sections. The general approach could potentially aid the development of numerical modeling techniques aimed at providing a systematic guideline geared toward developing microwave and RF photonic sources for THz applications.

  13. Anapole nanolasers for mode-locking and ultrafast pulse generation

    KAUST Repository

    Gongora, J. S. Totero

    2017-05-31

    Nanophotonics is a rapidly developing field of research with many suggestions for a design of nanoantennas, sensors and miniature metadevices. Despite many proposals for passive nanophotonic devices, the efficient coupling of light to nanoscale optical structures remains a major challenge. In this article, we propose a nanoscale laser based on a tightly confined anapole mode. By harnessing the non-radiating nature of the anapole state, we show how to engineer nanolasers based on InGaAs nanodisks as on-chip sources with unique optical properties. Leveraging on the near-field character of anapole modes, we demonstrate a spontaneously polarized nanolaser able to couple light into waveguide channels with four orders of magnitude intensity than classical nanolasers, as well as the generation of ultrafast (of 100 fs) pulses via spontaneous mode locking of several anapoles. Anapole nanolasers offer an attractive platform for monolithically integrated, silicon photonics sources for advanced and efficient nanoscale circuitry.

  14. Multiple-Pulse Operation and Bound States of Solitons in Passive Mode-Locked Fiber Lasers

    Directory of Open Access Journals (Sweden)

    A. Komarov

    2012-01-01

    Full Text Available We present results of our research on a multiple-pulse operation of passive mode-locked fiber lasers. The research has been performed on basis of numerical simulation. Multihysteresis dependence of both an intracavity energy and peak intensities of intracavity ultrashort pulses on pump power is found. It is shown that the change of a number of ultrashort pulses in a laser cavity can be realized by hard as well as soft regimes of an excitation and an annihilation of new solitons. Bound steady states of interacting solitons are studied for various mechanisms of nonlinear losses shaping ultrashort pulses. Possibility of coding of information on basis of soliton trains with various bonds between neighboring pulses is discussed. The role of dispersive wave emitted by solitons because of lumped intracavity elements in a formation of powerful soliton wings is analyzed. It is found that such powerful wings result in large bounding energies of interacting solitons in steady states. Various problems of a soliton interaction in passive mode-locked fiber lasers are discussed.

  15. Modelling and characterization of colliding-pulse mode-locked (CPM) quantum well lasers. [MPS1

    DEFF Research Database (Denmark)

    Bischoff, Svend; Brorson, S.D.; Franck, T.

    1996-01-01

    A theoretical and experimental study of passive colliding pulse mode-locked quantum well lasers is presented. The theoretical model for the gain dynamics is based on semi-classical density matrixequations. The gain dynamics are characterized exp...

  16. Structure of picosecond pulses of a Q-switched and mode-locked diode-pumped Nd:YAG laser

    Science.gov (United States)

    Donin, V. I.; Yakovin, D. V.; Gribanov, A. V.

    2015-12-01

    The pulse duration of a diode-pumped Nd:YAG laser, in which Q-switching with mode-locking (QML regime) is achieved using a spherical mirror and a travelling-wave acousto-optic modulator, is directly measured with a streak camera. It is found that the picosecond pulses can have a non-single-pulse structure, which is explained by excitation of several competing transverse modes in the Q-switching regime with a pulse repetition rate of 1 kHz. In the case of cw mode-locking (without Q-switching), a new (auto-QML) regime is observed, in which the pulse train repetition rate is determined by the frequency of the relaxation oscillations of the laser field while the train contains single picosecond pulses.

  17. Structure of picosecond pulses of a Q-switched and mode-locked diode-pumped Nd:YAG laser

    Energy Technology Data Exchange (ETDEWEB)

    Donin, V I; Yakovin, D V; Gribanov, A V [Institute of Automation and Electrometry, Siberian Branch of the Russian Academy of Sciences, Novosibirsk (Russian Federation)

    2015-12-31

    The pulse duration of a diode-pumped Nd:YAG laser, in which Q-switching with mode-locking (QML regime) is achieved using a spherical mirror and a travelling-wave acousto-optic modulator, is directly measured with a streak camera. It is found that the picosecond pulses can have a non-single-pulse structure, which is explained by excitation of several competing transverse modes in the Q-switching regime with a pulse repetition rate of 1 kHz. In the case of cw mode-locking (without Q-switching), a new (auto-QML) regime is observed, in which the pulse train repetition rate is determined by the frequency of the relaxation oscillations of the laser field while the train contains single picosecond pulses. (control of laser radiation parameters)

  18. High peak power sub-nanosecond mode-locked pulse characteristics of Nd:GGG laser

    Science.gov (United States)

    Zhao, Jia; Zhao, Shengzhi; Li, Tao; Li, Yufei; Yang, Kejian; Li, Guiqiu; Li, Dechun; Qiao, Wenchao; Feng, Chuansheng; Wang, Yonggang

    2015-10-01

    Based on the dual-loss modulation, i.e. electro-optic (EO) modulator and GaAs saturable absorber, a sub-nanosecond mode-locked pulsed Nd:GGG laser with kHz repetition rates is presented for the first time. The repetition rate (0.5-10 kHz) of this pulsed laser is controlled by the modulation rate of EO modulator, so high stability can be obtained. The sub-nanosecond pulse width depends on the mode-locked pulse underneath the Q-switched envelope in the Q-switched mode-locked (QML) laser and high peak power can be generated. The condition on the generation of sub-nanosecond pulse and the needed threshold power for different modulation rates of EO are given. The average output power, the pulse width and the peak power versus pump power for different repetition rates are demonstrated. The shortest pulse width is 426 ps and the highest peak power reaches 239.4 kW. The experimental results show that the dual-loss modulation technology with EO and GaAs saturable absorber in QML laser is an efficient method to generate sub-nanosecond mode-locked pulsed laser with kHz repetition rates.

  19. 40-gHz, 100-fs stimulated-Brillouin-scattering-free pulse generation by combining a mode-locked laser diode and a dispersion-decreasing fiber.

    Science.gov (United States)

    Hagiuda, Ken-ichi; Hirooka, Toshihiko; Nakazawa, Masataka; Arahira, Shin; Ogawa, Yoh

    2005-03-15

    A 40-GHz, 100-fs pulse train was successfully generated by soliton compression of a mode-locked laser diode (MLLD) pulse with a dispersion-decreasing fiber. The MLLD had a longitudinal mode linewidth as broad as 60 MHz, which made it possible to suppress stimulated Brillouin scattering and achieve stable, ultrahigh-speed pulse compression without applying external frequency modulation.

  20. On the jitter of mode-locked pulses introduced by an optical fibre

    NARCIS (Netherlands)

    Mols, R.F.X.A.M.; Mols, R.F.X.A.M.; Ernst, G.J.

    1993-01-01

    Measurements on the jitter of mode-locked pulses of a Nd:YLF laser after travelling through an optical fibre are presented. For low powers self phase modulation occurs which leaves the jitter unaltered. For powers higher than the threshold of stimulated Raman scattering the jitter increases due to

  1. Gain broadening and mode-locking in overcoupled second harmonic Q-switched microsecond pulses

    Science.gov (United States)

    Rohde, Ingo; Brinkmann, Ralf

    2014-10-01

    An intracavity frequency doubled, Q-switched Nd:YLF emitting at a wavelength of 527 nm was designed with the goal to temporally stretch the Q-switched pulses up to some microseconds at pulse energies of several millijoules. With different resonator configurations pulse durations between 12 μs and 3 μs with energies of 1 mJ-4.5 mJ have been achieved, which is demanded for an application in ophthalmology. For tighter intracavity foci and high pump power, however, strong power modulations by trains of picosecond pulses on the rear flank of the microsecond pulses were observed, indicating the occurrence of cascading nonlinearities and mode-locking. Simultaneously a significant increase of the fundamental spectrum up to 5 nm was found. A similar effect, which is referred to as gain broadening, has previously been observed by using ppKTP for intracavity second harmonic generation. This is, to the best of our knowledge, the first observation of this effect with unpoled second harmonic media. This project was realized with the support of the German Ministry for Education and Research (BMBF).

  2. Q-switching and mode-locking pulse generation with graphene oxide paper-based saturable absorber

    Directory of Open Access Journals (Sweden)

    Sulaiman Wadi Harun

    2015-06-01

    Full Text Available Q-switched and mode-locked erbium-doped fibre lasers (EDFLs are demonstrated by using non-conductive graphene oxide (GO paper as a saturable absorber (SA. A stable and self-starting Q-switched operation was achieved at 1534.4 nm by using a 0.8 m long erbium-doped fibre (EDF as a gain medium. The pulse repetition rate changed from 14.3 to 31.5 kHz, whereas the corresponding pulse width decreased from 32.8 to 13.8 µs as the pump power increased from 22 to 50.5 mW. A narrow spacing dual-wavelength Q-switched EDFL could also be realised by including a photonics crystal fibre and a tunable Bragg filter in the setup. It can operate at a maximum repetition rate of 31 kHz, with a pulse duration of 7.04 µs and pulse energy of 2.8 nJ. Another GOSA was used to realise mode-locked EDFL in a different cavity consisting of a 1.6 m long EDF in conjunction with 1480 nm pumping. The laser generated a soliton pulse train with a repetition rate of 15.62 MHz and pulse width of 870 fs. It is observed that the proposed fibre lasers have a low pulsing threshold pump power as well as a low damage threshold.

  3. Tungsten diselenide for mode-locked erbium-doped fiber lasers with short pulse duration

    Science.gov (United States)

    Liu, Wenjun; Liu, Mengli; OuYang, Yuyi; Hou, Huanran; Ma, Guoli; Lei, Ming; Wei, Zhiyi

    2018-04-01

    In this paper, a WSe2 film prepared by chemical vapor deposition (CVD) is transferred onto a tapered fiber, and a WSe2 saturable absorber (SA) is fabricated. In order to measure the third-order optical nonlinearity of the WSe2, the Z-scan technique is applied. The modulation depth of the WSe2 SA is measured as being 21.89%. Taking advantage of the remarkable nonlinear absorption characteristic of the WSe2 SA, a mode-locked erbium-doped fiber laser is demonstrated at 1557.4 nm with a bandwidth of 25.8 nm and signal to noise ratio of 96 dB. To the best of our knowledge, the pulse duration of 163.5 fs is confirmed to be the shortest compared with previous mode-locked fiber lasers based on transition-metal dichalcogenides SAs. These results indicate that WSe2 is a powerful competitor in the application of ultrashort pulse lasers.

  4. Mid-infrared mode-locked pulse generation with multilayer black phosphorus as saturable absorber.

    Science.gov (United States)

    Qin, Zhipeng; Xie, Guoqiang; Zhao, Chujun; Wen, Shuangchun; Yuan, Peng; Qian, Liejia

    2016-01-01

    A mid-infrared saturable absorber mirror is successfully fabricated by transferring the mechanically exfoliated black phosphorus onto the gold-coated mirror. With the as-prepared black phosphorus saturable absorber mirror, a continuous-wave passively mode-locked Er:ZBLAN fiber laser is demonstrated at the wavelength of 2.8 μm, which delivers a maximum average output power of 613 mW, a repetition rate of 24 MHz, and a pulse duration of 42 ps. To the best of our knowledge, this is the first time a black phosphorus mode-locked laser at 2.8 μm wavelength has been demonstrated. Our results demonstrate the feasibility of black phosphorus flake as a new two-dimensional material for application in mid-infrared ultrafast photonics.

  5. Chair-like pulses in an all-normal dispersion Ytterbium-doped mode-locked fiber laser.

    Science.gov (United States)

    Gupta, Pradeep K; Singh, Chandra P; Singh, Amarjeet; Sharma, Sunil K; Mukhopadhyay, Pranab K; Bindra, Kushvinder S

    2016-12-10

    We report, for what we believe is the first time, generation of stable chair-like pulses (a pulse shape with an initial long flat portion followed by a short high peak power portion resembling the shape of a chair) by mode locking of a Ytterbium (Yb)-doped fiber laser. Chair-like pulse shapes are achieved by implementing dual saturable absorbers, one based on a nonlinear optical loop mirror (NOLM) and the other based on nonlinear polarization rotation (NPR) inside the cavity. The transmission characteristics of the NOLM-NPR pair leading to the formation of chair-like pulses are numerically investigated. We also report the amplification characteristics of chair-like pulses in an external multistage Yb-doped fiber amplifier setup at different repetition rates of the pulse train. It was found that the chair-like pulses are suitable for amplification, and more than 10 W of average power at 460 kHz repetition rate have been obtained at total pump power of ∼20  W coupled to the power amplifier. At a lower repetition rate (115 kHz), ∼8  W of average power were obtained corresponding to ∼70  μJ of pulse energy with negligible contribution from amplified spontaneous emission or stimulated Raman scattering. We believe that such an oscillator-amplifier system could serve as an attractive tool for micromachining applications.

  6. High-power femtosecond pulse generation in a passively mode-locked Nd:SrLaAlO4 laser

    Science.gov (United States)

    Liu, Shan-De; Dong, Lu-Lu; Zheng, Li-He; Berkowski, Marek; Su, Liang-Bi; Ren, Ting-Qi; Peng, Yan-Dong; Hou, Jia; Zhang, Bai-Tao; He, Jing-Liang

    2016-07-01

    A high optical quality Nd:SrLaAlO4 (Nd:SLA) crystal was grown using the Czochralski method and showed broad fluorescence spectrum with a full width at half maximum value of 34 nm, which is beneficial for generating femtosecond laser pulses. A stable diode-pumped passively mode-locked femtosecond Nd:SLA laser with 458 fs pulse duration was achieved for the first time at a central wavelength of 1077.9 nm. The average output power of the continuous-wave mode-locked laser was 520 mW and the repetition rate was 78.5 MHz.

  7. Electrical addressing and temporal tweezing of localized pulses in passively mode-locked semiconductor lasers

    Science.gov (United States)

    Javaloyes, J.; Camelin, P.; Marconi, M.; Giudici, M.

    2017-08-01

    This work presents an overview of a combined experimental and theoretical analysis on the manipulation of temporal localized structures (LSs) found in passively Vertical-Cavity Surface-Emitting Lasers coupled to resonant saturable absorber mirrors. We show that the pumping current is a convenient parameter for manipulating the temporal Localized Structures, also called localized pulses. While short electrical pulses can be used for writing and erasing individual LSs, we demonstrate that a current modulation introduces a temporally evolving parameter landscape allowing to control the position and the dynamics of LSs. We show that the localized pulses drifting speed in this landscape depends almost exclusively on the local parameter value instead of depending on the landscape gradient, as shown in quasi-instantaneous media. This experimental observation is theoretically explained by the causal response time of the semiconductor carriers that occurs on an finite timescale and breaks the parity invariance along the cavity, thus leading to a new paradigm for temporal tweezing of localized pulses. Different modulation waveforms are applied for describing exhaustively this paradigm. Starting from a generic model of passive mode-locking based upon delay differential equations, we deduce the effective equations of motion for these LSs in a time-dependent current landscape.

  8. 256 fs, 2 nJ soliton pulse generation from MoS2 mode-locked fiber laser

    Science.gov (United States)

    Jiang, Zike; Chen, Hao; Li, Jiarong; Yin, Jinde; Wang, Jinzhang; Yan, Peiguang

    2017-12-01

    We demonstrate an Er-doped fiber laser (EDFL) mode-locked by a MoS2 saturable absorber (SA), delivering a 256 fs, 2 nJ soliton pulse at 1563.4 nm. The nonlinear property of the SA prepared by magnetron sputtering deposition (MSD) is measured with a modulation depth (MD) of ∼19.48% and a saturable intensity of 4.14 MW/cm2. To the best of our knowledge, the generated soliton pulse has the highest pulse energy of 2 nJ among the reported mode-locked EDFLs based on transition metal dichalcogenides (TMDs). Our results indicate that MSD-grown SAs could offer an exciting platform for high pulse energy and ultrashort pulse generation.

  9. Design and Applications of In-Cavity Pulse Shaping by Spectral Sculpturing in Mode-Locked Fibre Lasers

    Directory of Open Access Journals (Sweden)

    Sonia Boscolo

    2015-11-01

    Full Text Available We review our recent progress on the realisation of pulse shaping in passively-mode-locked fibre lasers by inclusion of an amplitude and/or phase spectral filter into the laser cavity. We numerically show that depending on the amplitude transfer function of the in-cavity filter, various regimes of advanced waveform generation can be achieved, including ones featuring parabolic-, flat-top- and triangular-profiled pulses. An application of this approach using a flat-top spectral filter is shown to achieve the direct generation of high-quality sinc-shaped optical Nyquist pulses with a widely tunable bandwidth from the laser oscillator. We also present the operation of an ultrafast fibre laser in which conventional soliton, dispersion-managed soliton (stretched-pulse and dissipative soliton mode-locking regimes can be selectively and reliably targeted by adaptively changing the dispersion profile and bandwidth programmed on an in-cavity programmable filter. The results demonstrate the strong potential of an in-cavity spectral pulse shaper for achieving a high degree of control over the dynamics and output of mode-locked fibre lasers.

  10. 50-fs pulse generation directly from a colliding-pulse mode-locked Ti:sapphire laser using an antiresonant ring mirror

    Science.gov (United States)

    Naganuma, Kazunori; Mogi, Kazuo

    1991-05-01

    50-fs pulses were directly generated from a colliding-pulse mode-locked Ti:sapphire laser. To achieve the colliding-pulse mode locking, a miniature antiresonant ring containing an organic saturable dye jet was employed as the end mirror for the linear cavity laser. Based on measured dispersion of intracavity elements, a prism pair was implemented to control the cavity dispersion. The generated pulses have no linear chirp but do exhibit parabolic instantaneous frequency owing to third-order dispersion introduced by the prism pair.

  11. Second-order fractional Talbot effect induced frequency-doubling optical pulse injection for 40 GHz rational-harmonic mode-locking of an SOA fiber laser

    Science.gov (United States)

    Kang, Jung-Jui; Lin, Yung-Hsiang; Lee, Chao-Kuei; Lin, Gong-Ru

    2013-09-01

    A second-order fractional Talbot effect induced frequency-doubling of a 10 GHz optical pulse-train is demonstrated to backward injection mode-lock a semiconductor optical amplifier fiber laser (SOAFL) for 40 GHz rational-harmonic mode-locking (RHML). That is, a real all-optical gain-modulation of the SOAFL can be created by injecting such a time-multiplexed but pseudo-frequency-doubled pulse-train into the cavity. The time-multiplexing pulse-train can thus be transformed into a frequency-multiplied pulse-train via cross-gain modulation (XGM). The optical pulse-train at 10 GHz is generated by nonlinearly driving an electro-absorption modulator (EAM), which experiences the second-order fractional Talbot effect after propagating through a 4 km long dispersion compensation fiber (DCF). The DCF not only plays the role of frequency-doubler but also compensates the frequency chirp of the 10 GHz optical pulse-train. The pulsewidth broadening from 22 to 60 ps for initiating the time-domain Talbot effect is simulated by the nonlinear Schrödinger equation. With careful detuning of the RF modulation power of the EAM at 5 dBm, the generated 20 GHz optical pulse-train exhibits a positive frequency chirp with minimum peak-to-peak value of 2 GHz, and the peak-amplitude fluctuation between adjacent pulses is below 1.4%. In comparison with the SOAFL pulse-train repeated at 40 GHz generated by the fourth-order purely RHML process, the optimized second-order fractional Talbot effect in combination with the second-order RHML mechanism significantly enhances the modulation-depth of RHML, thus improving the on/off extinction ratio of the 40 GHz SOAFL pulse-train from 1.8 to 5.6 dB. Such a new scheme also provides a more stable 40 GHz RHML pulse-train from the SOAFL with its timing jitter reducing from 0.51 to 0.23 ps.

  12. Q-switched-like soliton bunches and noise-like pulses generation in a partially mode-locked fiber laser.

    Science.gov (United States)

    Wang, Zhenhong; Wang, Zhi; Liu, Yan-Ge; Zhao, Wenjing; Zhang, Hao; Wang, Shangcheng; Yang, Guang; He, Ruijing

    2016-06-27

    We report an intermediate regime between c.w. emission and noise-like pulses (NLPs) regime in an Er-doped partially mode-locked fiber laser with nonlinear polarization rotation. In this regime, the soliton bunches stochastically turn up from a quasi-cw background in the Q-switched-like envelope. The soliton bunches normally last for tens or hundreds of intracavity round-trips. When the soliton bunches vanish, typical NLPs chains are generated sporadically at location where the soliton bunches collapses. These results would be helpful to understand the generation and property of the NLPs regime.

  13. Continuous-wave to pulse regimes for a family of passively mode-locked lasers with saturable nonlinearity

    Science.gov (United States)

    Dikandé, Alain M.; Voma Titafan, J.; Essimbi, B. Z.

    2017-10-01

    The transition dynamics from continuous-wave to pulse regimes of operation for a generic model of passively mode-locked lasers with saturable absorbers, characterized by an active medium with non-Kerr nonlinearity, are investigated analytically and numerically. The system is described by a complex Ginzburg-Landau equation with a general m:n saturable nonlinearity (i.e {I}m/{(1+{{Γ }}I)}n, where I is the field intensity and m and n are two positive numbers), coupled to a two-level gain equation. An analysis of stability of continuous waves, following the modulational instability approach, provides a global picture of the self-starting dynamics in the system. The analysis reveals two distinct routes depending on values of the couple (m, n), and on the dispersion regime: in the normal dispersion regime, when m = 2 and n is arbitrary, the self-starting requires positive values of the fast saturable absorber and nonlinearity coefficients, but negative values of these two parameters for the family with m = 0. However, when the spectral filter is negative, the laser can self-start for certain values of the input field and the nonlinearity saturation coefficient Γ. The present work provides a general map for the self-starting mechanisms of rare-earth doped figure-eight fiber lasers, as well as Kerr-lens mode-locked solid-state lasers.

  14. Actively mode-locked Raman fiber laser.

    Science.gov (United States)

    Yang, Xuezong; Zhang, Lei; Jiang, Huawei; Fan, Tingwei; Feng, Yan

    2015-07-27

    Active mode-locking of Raman fiber laser is experimentally investigated for the first time. An all fiber connected and polarization maintaining loop cavity of ~500 m long is pumped by a linearly polarized 1120 nm Yb fiber laser and modulated by an acousto-optic modulator. Stable 2 ns width pulse train at 1178 nm is obtained with modulator opening time of > 50 ns. At higher power, pulses become longer, and second order Raman Stokes could take place, which however can be suppressed by adjusting the open time and modulation frequency. Transient pulse evolution measurement confirms the absence of relaxation oscillation in Raman fiber laser. Tuning of repetition rate from 392 kHz to 31.37 MHz is obtained with harmonic mode locking.

  15. Ultrashort pulse generation in mode-locked erbium-doped fiber lasers with tungsten disulfide saturable absorber

    Science.gov (United States)

    Liu, Mengli; Liu, Wenjun; Pang, Lihui; Teng, Hao; Fang, Shaobo; Wei, Zhiyi

    2018-01-01

    Tungsten disulfide (WS2), as one of typical transition metal dichalcogenides with the characteristics of strong nonlinear polarization and wide bandgap, has been widely used in such fields as biology and optoelectronics. With the magnetron sputtering technique, the saturable absorber (SA) is prepared by depositing WS2 and Au film on the tapered fiber. The heat elimination and damage threshold can be improved for the WS2 SA with evanescent field interaction. Besides, the Au film is deposited on the surface of the WS2 film to improve their reliability and avoid being oxidized. The fabricated SA has a modulation depth of 14.79%. With this SA, we obtain a relatively stable mode-locked fiber laser with the pulse duration of 288 fs, the repetition rate of 41.4 MHz and the signal to noise ratio of 58 dB.

  16. Comb multi-wavelength, rectangular pulse, passively mode-locked fiber laser enhanced by un-pumped Erbium-doped fiber

    Science.gov (United States)

    Guo, Chunyu; Luo, Ruoheng; Liu, Weiqi; Ruan, Shuangchen; Yang, Jinhui; Yan, Peiguang; Wang, Jinzhang; Hua, Ping

    2018-01-01

    We propose and demonstrate a comb multi-wavelength, nanosecond rectangular pulse, passively mode-locked Erbium-doped fiber (EDF) laser. A section of un-pumped EDF had been employed to optimize the multi-wavelength pulses for the first time to the best of our knowledge. The un-pumped EDF absorbs the unwanted the short-wavelength lasing and optimizes the gain, therefore allowing for the enhancement of the long-wavelength lasing. Because of the gain competition effect in the un-pumped EDF, the output wavelength line number of the fiber laser can be significantly increased from three wavelengths to twenty lasing wavelengths. The mode-locked pulse has a rectangular temporal profile with pump power dependent pulse duration. Experimental results illustrate that the fiber laser has a good stability at room temperature. This work provides a new configuration for the design of multi-wavelength, rectangular nanosecond pulse that may fit for specific applications.

  17. Generation of 103 fs mode-locked pulses by a gain linewidth-variable Nd,Y:CaF2 disordered crystal.

    Science.gov (United States)

    Qin, Z P; Xie, G Q; Ma, J; Ge, W Y; Yuan, P; Qian, L J; Su, L B; Jiang, D P; Ma, F K; Zhang, Q; Cao, Y X; Xu, J

    2014-04-01

    We have demonstrated a diode-pumped passively mode-locked femtosecond Nd,Y:CaF2 disordered crystal laser for the first time to our knowledge. By choosing appropriate Y-doping concentration, a broad fluorescence linewidth of 31 nm has been obtained from the gain linewidth-variable Nd,Y:CaF2 crystal. With the Nd,Y:CaF2 disordered crystal as gain medium, the mode-locked laser generated pulses with pulse duration as short as 103 fs, average output power of 89 mW, and repetition rate of 100 MHz. To our best knowledge, this is the shortest pulse generated from Nd-doped crystal lasers so far. The research results show that the Nd,Y:CaF2 disordered crystal will be a potential alternative as gain medium of repetitive chirped pulse amplification for high-peak-power lasers.

  18. The simultaneous generation of soliton bunches and Q-switched-like pulses in a partially mode-locked fiber laser with a graphene saturable absorber

    Science.gov (United States)

    Wang, Zhenhong; Wang, Zhi; Liu, Yan-ge; He, Ruijing; Wang, Guangdou; Yang, Guang; Han, Simeng

    2018-05-01

    We experimentally report the coexistence of soliton bunches and Q-switched-like pulses in a partially mode-locked fiber laser with a microfiber-based graphene saturable absorber. The soliton bunches, like isolated spikes with extreme amplitude and ultrashort duration, randomly generate in the background of the Q-switched-like pulses. The soliton bunches have some pulse envelopes in which pulses operate at a fundamental repetition rate in the temporal domain. Further investigation shows that the composite pulses are highly correlated with the noise-like pulses. Our work can make a further contribution to enrich the understanding of the nonlinear dynamics in fiber lasers.

  19. Characterisation of the light pulses of a cavity dumped dye laser pumped by a cw mode-locked and q-switched Nd:YAG laser

    International Nuclear Information System (INIS)

    Geist, P.; Heisel, F.; Martz, A.; Miehe, J.A.; Miller, R.J.D.

    1984-01-01

    The frequency doubled pulses (of 532 nm) obtained, with the help of a KTP crystal, from those delivered by either a continuous wave mode-locked (100 MHz) or mode-locked Q-switched (0-1 KHz) Nd: YAG laser, are analyzed by means of a streak camera, operating in synchroscan or triggered mode. In the step-by-step measurements the pulse stability, concerning form and amplitude, is shown. In addition, measurements effectuated with synchronously pumped and cavity dumped dye laser (Rhodamine 6G), controlled by a Pockels cell, allows the obtention of stable and reproducible single pulses of 30 ps duration, 10 μJ energy and 500Hz frequency [fr

  20. Low-timing-jitter, stretched-pulse passively mode-locked fiber laser with tunable repetition rate and high operation stability

    International Nuclear Information System (INIS)

    Liu, Yuanshan; Zhang, Jian-Guo; Chen, Guofu; Zhao, Wei; Bai, Jing

    2010-01-01

    We design a low-timing-jitter, repetition-rate-tunable, stretched-pulse passively mode-locked fiber laser by using a nonlinear amplifying loop mirror (NALM), a semiconductor saturable absorber mirror (SESAM), and a tunable optical delay line in the laser configuration. Low-timing-jitter optical pulses are stably produced when a SESAM and a 0.16 m dispersion compensation fiber are employed in the laser cavity. By inserting a tunable optical delay line between NALM and SESAM, the variable repetition-rate operation of a self-starting, passively mode-locked fiber laser is successfully demonstrated over a range from 49.65 to 50.47 MHz. The experimental results show that the newly designed fiber laser can maintain the mode locking at the pumping power of 160 mW to stably generate periodic optical pulses with width less than 170 fs and timing jitter lower than 75 fs in the 1.55 µm wavelength region, when the fundamental repetition rate of the laser is continuously tuned between 49.65 and 50.47 MHz. Moreover, this fiber laser has a feature of turn-key operation with high repeatability of its fundamental repetition rate in practice

  1. Influence of different approaches for dynamical performance optimization of monolithic passive colliding-pulse mode-locked laser diodes emitting around 850 nm

    Science.gov (United States)

    Prziwarka, T.; Klehr, A.; Wenzel, H.; Fricke, J.; Bugge, F.; Weyers, M.; Knigge, A.; Tränkle, G.

    2018-02-01

    Monolithic laser diodes which generate short infrared pulses in the picosecond and sub-picosecond ranges with high peak power are ideal sources for many applications like e.g. THz-time-domain spectroscopy (TDS) scanning systems. The achievable THz bandwidth is limited by the length of the optical pulses. Due to the fact that colliding-pulse mode locking (CPM) leads to the shortest pulses which could reached by passive mode locking, we experimentally investigated in detail the dynamical and electro optical performance of InGaAsP based quantum well CPM laser diodes with well-established vertical layer structures. Simple design modifications whose implementation is technically easy were realized. Improvements of the device performance in terms of pulse duration, output power, and noise properties are presented in dependence on the different adaptions. From the results we extract an optimized configuration with which we have reached pulses with durations of ≍1.5 ps, a peak power of > 1 W and a pulse-to-pulse timing jitter < 200 fs. The laser diodes emit pulses at a wavelength around 850 nm with a repetition frequency of ≍ 12.4 GHz and could be used as pump source for GaAs antennas to generate THz-radiation. Approaches for reducing pulse width, increasing output power, and improving noise performance are described.

  2. High average/peak power linearly polarized all-fiber picosecond MOPA seeded by mode-locked noise-like pulses

    Science.gov (United States)

    Yu, H. L.; Ma, P. F.; Tao, R. M.; Wang, X. L.; Zhou, P.; Chen, J. B.

    2015-06-01

    The characteristics of mode-locked noise-like pulses generated from a passively mode-locked fiber oscillator are experimentally investigated. By carefully adjusting the two polarization controllers, stable mode-locked noise-like pulse emission with a high radio frequency signal/noise ratio of  >55 dB is successfully achieved, ensuring the safety and possibility of high power amplification. To investigate the amplification characteristics of such pulses, one all-fiber master oscillator power amplifier (MOPA) is built to boost the power and energy of such pulses. Amplified noise-like pulses with average output power of 423 W, repetition rate of 18.71 MHz, pulse energy of 22.61 μJ, pulse duration of 72.1 ps and peak power of 314 kW are obtained. Near diffraction-limited beam is also demonstrated with M2 factor measured at full power operation of ~1.2 in the X and Y directions. The polarization extinction ratio at output power of 183 W is measured to be ~13 dB. To the best of our knowledge, this is the first demonstration of high-power amplification of noise-like pulses and the highest peak power ever reported in all-fiber picosecond MOPAs. The temporal self-compression process of such pulses and high peak power when amplified make it an ideal pump source for generation of high-power supercontinuum. Other potential applications, such as material processing and optical coherent tomography, could also be foreseen.

  3. An automatic mode-locked system for passively mode-locked fiber laser

    Science.gov (United States)

    Li, Sha; Xu, Jun; Chen, Guoliang; Mei, Li; Yi, Bo

    2013-12-01

    This paper designs and implements one kind of automatic mode-locked system. It can adjust a passively mode-locked fiber laser to keep steady mode-locked states automatically. So the unsteadiness of traditional passively mode-locked fiber laser can be avoided. The system transforms optical signals into electrical pulse signals and sends them into MCU after processing. MCU calculates the frequency of the signals and judges the state of the output based on a quick judgment algorithm. A high-speed comparator is used to check the signals and the comparison voltage can be adjusted to improve the measuring accuracy. Then by controlling two polarization controllers at an angle of 45degrees to each other, MCU extrudes the optical fibers to change the polarization until it gets proper mode-locked output. So the system can continuously monitor the output signal and get it back to mode-locked states quickly and automatically. States of the system can be displayed on the LCD and PC. The parameters of the steady mode-locked states can be stored into an EEPROM so that the system will get into mode-locked states immediately next time. Actual experiments showed that, for a 6.238MHz passively mode-locked fiber lasers, the system can get into steady mode-locked states automatically in less than 90s after starting the system. The expected lock time can be reduced to less than 20s after follow up improvements.

  4. Vortex states near absolute zero in a weak-pinning amorphous Mo x Ge1-x film probed by pulsed mode-locking resonance

    Science.gov (United States)

    Sohara, N.; Ochi, A.; Murakami, E.; Ienaga, K.; Kaneko, S.; Kokubo, N.; Okuma, S.

    2017-07-01

    We have developed measurements of the mode-locking (ML) resonance with pulsed currents, which generates much less heat than the conventional one with continuous currents. Here, we present the experimental details of the pulsed ML measurement. Using this technique, we have succeeded in determining the dynamic melting field of a driven vortex lattice for a weak-pinning thick amorphous Mo x Ge1-x film down to 0.05 K. We construct an ideal vortex phase diagram in the absence of pinning near zero temperature as a function of magnetic field.

  5. Mode-locking peculiarities in an all-fiber erbium-doped ring ultrashort pulse laser with a highly-nonlinear resonator

    Science.gov (United States)

    Dvoretskiy, Dmitriy A.; Sazonkin, Stanislav G.; Kudelin, Igor S.; Orekhov, Ilya O.; Pnev, Alexey B.; Karasik, Valeriy E.; Denisov, Lev K.

    2017-12-01

    Today ultrashort pulse (USP) fiber lasers are in great demand in a frequency metrology field, THz pulse spectroscopy, optical communication, quantum optics application, etc. Therefore mode-locked (ML) fiber lasers have been extensively investigated over the last decade due the number of scientific, medical and industrial applications. It should be noted, that USP fiber lasers can be treated as an ideal platform to expand future applications due to the complex ML nonlinear dynamics in a laser resonator. Up to now a series of novel ML regimes have been investigated e.g. self-similar pulses, noise-like pulses, multi-bound solitons and soliton rain generation. Recently, we have used a highly nonlinear germanosilicate fiber (with germanium oxides concentration in the core 50 mol. %) inside the resonator for more reliable and robust launching of passive mode-locking based on the nonlinear polarization evolution effect in fibers. In this work we have measured promising and stable ML regimes such as stretched pulses, soliton rain and multi-bound solitons formed in a highly-nonlinear ring laser and obtained by intracavity group velocity dispersion (GVD) variation in slightly negative region. As a result, we have obtained the low noise ultrashort pulse generation with duration 59 dB) and relative intensity noise <-101 dBc / Hz.

  6. Delay differential equations for mode-locked semiconductor lasers.

    Science.gov (United States)

    Vladimirov, Andrei G; Turaev, Dmitry; Kozyreff, Gregory

    2004-06-01

    We propose a new model for passive mode locking that is a set of ordinary delay differential equations. We assume a ring-cavity geometry and Lorentzian spectral filtering of the pulses but do not use small gain and loss and weak saturation approximations. By means of a continuation method, we study mode-locking solutions and their stability. We find that stable mode locking can exist even when the nonlasing state between pulses becomes unstable.

  7. High-pulse energy-stabilized passively mode-locked external cavity inverse bow-tie 980nm laser diode for space applications

    Science.gov (United States)

    Krakowski, M.; Resneau, P.; Garcia, M.; Vinet, E.; Robert, Y.; Lecomte, M.; Parillaud, O.; Gerard, B.; Kundermann, S.; Torcheboeuf, N.; Boiko, D. L.

    2018-02-01

    We report on multi-section inverse bow-tie laser producing mode-locked pulses of 90 pJ energy and 6.5 ps width (895 fs after compression) at 1.3 GHz pulse repetition frequency (PRF) and consuming 2.9 W of electric power. The laser operates in an 80 mm long external cavity. By translation of the output coupling mirror, the PRF was continuously tuned over 37 MHz range without additional adjustments. Active stabilization with a phase lock loop actuating on the driving current has allowed us to reach the PRF relative stability at a 2·10-10 level on 10 s intervals, as required by the European Space Agency (ESA) for inter-satellite long distance measurements.

  8. Mode-locked silicon evanescent lasers.

    Science.gov (United States)

    Koch, Brian R; Fang, Alexander W; Cohen, Oded; Bowers, John E

    2007-09-03

    We demonstrate electrically pumped lasers on silicon that produce pulses at repetition rates up to 40 GHz. The mode locked lasers generate 4 ps pulses with low jitter and extinction ratios above 18 dB, making them suitable for data and telecommunication transmitters and for clock generation and distribution. Results of both passive and hybrid mode locking are discussed. This type of device could enable new silicon based integrated technologies, such as optical time division multiplexing (OTDM), wavelength division multiplexing (WDM), and optical code division multiple access (OCDMA).

  9. Directly phase-modulation-mode-locked doubly-resonant optical parametric oscillator.

    Science.gov (United States)

    Devi, Kavita; Kumar, S Chaitanya; Ebrahim-Zadeh, M

    2013-10-07

    We present results on direct mode-locking of a doubly-resonant optical parametric oscillator (DRO) using an electro-optic phase modulator with low resonant frequency of 80 MHz as the single mode-locking element. Pumped by a cw laser at 532 nm and based on MgO:sPPLT as the nonlinear material, the DRO generates 533 ps pulses at 80 MHz and 471 ps pulses at 160 MHz. Stable train of mode-locked pulses is obtained at a modulation depth of 1.83 radians when the modulation frequency is precisely tuned and the cavity length is carefully adjusted. The effects of frequency detuning, modulation depth, input laser pump power, crystal temperature and position of modulator inside the cavity, on pulse duration and repetition rate have been studied. Operating at degeneracy, under mode-locked condition, the signal-idler spectrum exhibits a bandwidth of ~31 nm, and the spectrum has been investigated for different phase-matching temperatures. Mode-locked operation has been confirmed by second-harmonic-generation of the DRO output in a β-BaB₂O₄ crystal, where a 4 times enhancement in green power is observed compared to cw operation.

  10. Soliton generation from a fundamentally mode-locked fiber laser with a feed-forward path

    Science.gov (United States)

    Wang, Ruixin; Dai, Yitang; Yin, Feifei; Xu, Kun; Li, Jianqiang; Lin, Jintong

    2014-08-01

    We demonstrate for the first time to our knowledge, the soliton generation from a mode-locked erbium-doped fiber laser using a novel saturable absorber (SA), which is realized by combining a dual-drive modulator and an intensity feed-forward path. The laser is fundamentally mode-locked under high-frequency RF signal modulation. Experimentally, the actively mode-locked laser produces a 16.7 MHz repetition rate pulse train with a 1.4 ps pulse width, and the spectrum bandwidth is 2.17 nm. The results demonstrate that the SA supports soliton pulse shaping in the cavity at the fundamental frequency.

  11. Design studies on compact four mirror laser resonator with mode-locked pulsed laser for 5 μm laser wire

    Energy Technology Data Exchange (ETDEWEB)

    Rawankar, Arpit [Department of Accelerator Science, School of High Energy Accelerator Science, Graduate University for Advanced Studies, Shonan International Village, Hayama, Miura, Kanagawa 240-0193 (Japan); High Energy Accelerator Research Organization KEK, 1-1 Oho, Tsukuba, Ibaraki 305-0801 (Japan); Urakawa, Junji, E-mail: junji.urakawa@kek.jp [Department of Accelerator Science, School of High Energy Accelerator Science, Graduate University for Advanced Studies, Shonan International Village, Hayama, Miura, Kanagawa 240-0193 (Japan); High Energy Accelerator Research Organization KEK, 1-1 Oho, Tsukuba, Ibaraki 305-0801 (Japan); Shimizu, Hirotaka [Department of Accelerator Science, School of High Energy Accelerator Science, Graduate University for Advanced Studies, Shonan International Village, Hayama, Miura, Kanagawa 240-0193 (Japan); You, Yan [Department of Engineering Physics, Tsinghua University, Beijing, 100084 (China); Terunuma, Nobuhiro [Department of Accelerator Science, School of High Energy Accelerator Science, Graduate University for Advanced Studies, Shonan International Village, Hayama, Miura, Kanagawa 240-0193 (Japan); High Energy Accelerator Research Organization KEK, 1-1 Oho, Tsukuba, Ibaraki 305-0801 (Japan); Aryshev, Alexander; Honda, Yosuke [High Energy Accelerator Research Organization KEK, 1-1 Oho, Tsukuba, Ibaraki 305-0801 (Japan)

    2013-02-01

    A compact prototype four-mirror optical cavity is being constructed at KEK-ATF to measure low-emittance electron beams in the damping ring. Four-mirror-resonators reduce the sensitivity to the misalignment of mirrors in comparison to two mirror-resonators. The aspect ratio is important when constructing a compact resonator with a very small beam waist of less than 5 μm. The total cavity length of a four-mirror resonator is matched according to the pulse repetition of mode-locked laser oscillator. Minimum beam waist is obtained in the sagittal plane using an IR pulsed laser. The advantage of such types of compact four-mirror-resonators is the total scanning time for measurement of the beam profile is much shorter in comparison to a CW laser wire system. By using a pulsed green laser that has been converted to the second harmonics from an IR pulsed laser, a minimum beam waist that has half the beam waist when using an IR laser oscillator can be obtained. Therefore, it is possible to obtain the beam waist of less than 5 μm (σ value) that is required for effective photon–electron collision. We report on the development and performance studies for such types of compact four-mirror laser wire systems.

  12. Flexible picosecond thulium-doped fiber laser using the active mode-locking technique.

    Science.gov (United States)

    Yin, Ke; Zhang, Bin; Yang, Weiqiang; Chen, He; Chen, Shengping; Hou, Jing

    2014-07-15

    An all-fiber actively mode-locked thulium-doped fiber laser (AML-TDFL) based on a 10 GHz bandwidth electro-optic intensity modulator (EOM) providing flexible picosecond pulses at 1980 nm is presented. The EOM is driven by electrical pulses rather than traditional sine-wave signals. The repetition rate of output pulses was 21.4 MHz at fundamental mode-locking, which could be scaled up to 1.498 GHz through the 70th order harmonic mode-locking, and the shortest measured output pulse width was 38 ps. Furthermore, the output pulse width could be tuned by either adjusting the modulation frequency with small detuning or changing the width of these driving electrical pulses without frequency detuning. In our work, the stability of these mode-locked pulses obtained from the AML-TDFL was superior; for instance, the measured supermode suppression ratio of 1.498 GHz pulses train was up to 48 dB.

  13. Mode-locked semiconductor laser for long and absolute distance measurement based on laser pulse repetition frequency sweeping: a comparative study between three types of lasers

    Science.gov (United States)

    Castro Alves, D.; Abreu, Manuel; Cabral, Alexandre; Rebordão, J. M.

    2017-08-01

    In this work we present a study on three types of semiconductor mode-locked lasers as possible sources for a high precision absolute distance metrology measurement concept based on pulse repetition frequency (PRF) sweep. In this work, we evaluated one vertical emission laser and two transversal emission sources. The topology of the gain element is quantum-well, quantum-dot and quantum-dash, respectively. Only the vertical emission laser has optical pump, whilst the others operate with electric pumping. The quantum-dash laser does not have a saturable absorber in its configuration but relies on a dispersion compensating fiber for generating pulses. The bottleneck of vertical emission laser is his high power density pump (4.5W/165μm), increasing the vulnerability of damaging the gain element. The other lasers, i.e., the single (quantum-dash) and double section (quantum-dot) lasers present good results either in terms of applicability to the metrology system or in terms of robustness. Using RF injection on the gain element, both lasers show good PRF stabilization results (better than σy(10ms) = 10-9 ) which is a requirement for the mentioned metrology technique.

  14. $CO_{2}$ laser ion source Comparison between mode-locked and free- running laser beams

    CERN Document Server

    Lisi, N; Scrivens, R

    2001-01-01

    The production of highly charged ions in a CO/sub 2/ laser-generated plasma is compared for different laser pulse-time structures. The work was performed at the CERN Laser Ion Source, which has the aim of developing a high current, high charge-state ion source for the Large Hadron Collider (LHC). When an intense laser pulse is focused onto a high-Z metal target, the ions expanding in the plasma plume are suitable for extraction from the plasma and matching into a synchrotron. For the first time, a comparison is made between free- running pulses with randomly fluctuating intensity, and mode-locked pulse trains with a reproducible structure and the same energy. Despite the lower power density with respect to the mode-locked pulse train, the free-running pulse provides higher charge states and higher yield. (10 refs).

  15. Jitter reduction by intracavity active phase modulation in a mode-locked semiconductor laser.

    Science.gov (United States)

    Ozharar, Sarper; Ozdur, Ibrahim; Quinlan, Franklyn; Delfyett, Peter J

    2009-03-01

    We experimentally verify the theory of Haus et al. [IEEE J. Quantum Electron. 40, 41 (2004)] on the effects of timing jitter using intracavity phase modulation on the pulse train of a mode-locked laser. The theory is based on the solution of the Heisenberg-Langevin equation in the presence of dispersion and intracavity phase modulation. Using active intracavity phase modulation, we have reduced the timing jitter on a 10.24 GHz mode-locked diode laser by 50% from 304 to 150 fs integrated from 1 Hz to the Nyquist frequency of 5.12 GHz.

  16. 260 fs and 1 nJ pulse generation from a compact, mode-locked Tm-doped fiber laser.

    Science.gov (United States)

    Sobon, Grzegorz; Sotor, Jaroslaw; Pasternak, Iwona; Krajewska, Aleksandra; Strupinski, Wlodek; Abramski, Krzysztof M

    2015-11-30

    We report on generation of 260 fs-short pulses with energy of 1.1 nJ from a fully fiberized, monolithic Tm-doped fiber laser system. The design comprises a simple, graphene-based ultrafast oscillator and an integrated all-fiber chirped pulse amplifier (CPA). The system generates 110 mW of average power at 100.25 MHz repetition rate and central wavelength of 1968 nm. This is, to our knowledge, the highest pulse energy generated from a fully fiberized sub-300 fs Tm-doped laser, without the necessity of using grating-based dispersion compensation. Such compact, robust and cost-effective system might serve as a seed source for nonlinear frequency conversion or mid-infrared supercontinuum generation.

  17. Q-Switched and Mode Locked Short Pulses from a Diode Pumped, YB-Doped Fiber Laser

    Science.gov (United States)

    2009-03-26

    polarization maintaining (PM) at a length of 8.7 ± 0.1 m. The surface area of the PANDA -style fiber is pictured in figure 3.3 (a) [46]. The core diameter was...diode- pumped c-cut Nd:GdVO4 laser,” Optics Communications 231 (2004) pg 365-369. 36. W. G. Wagner, B. A. Lengyel, "Evolution of the giant pulse in a

  18. Cr:ZnS saturable absorber passively Q-switched mode-locking Tm,Ho:LLF laser.

    Science.gov (United States)

    Zhang, Xinlu; Luo, Yong; Wang, Tianhan; Dai, Junfeng; Zhang, Jianxin; Li, Jiang; Cui, Jinhui; Huang, Jinjer

    2017-04-10

    We first report on a diode-end-pumped passively Q-switched mode-locking Tm,Ho:LLF laser at 2053 nm by using a Cr:ZnS saturable absorber. A stable Q-switched mode-locking pulse train with a nearly 100% modulation depth was achieved. The repetition frequency of the Q-switched pulse envelope increased from 0.5 to 12.3 kHz with increasing pump power from 1 to 4.36 W. The maximum average output power of 145 mW was obtained, and the width of the mode-locked pulse was estimated to be less than 682 ps with a 250 MHz repetition frequency within a Q-switched pulse envelope of about 700 ns.

  19. Effect of periodic optical pumping on dynamics of passive mode-locked fiber laser

    Science.gov (United States)

    Lee, Chung Ghiu; Kim, Joonyoung; Kim, Soeun

    2017-10-01

    We report on the effect of periodic optical pumping on a passively mode-locked fiber laser (MLFL) based on an erbium-doped fiber (EDF). We investigate the influence of various parameters (including average pump power into the fiber laser, the modulation frequency and duty cycle of the pump, and the polarization state of the light inside the cavity) on the transient response characteristic of the MLFL such as: relaxation oscillation (RO) build-up time (defined as the time delay from the onset of pumping to the generation of passively mode-locked pulses) and the power of the detected RF signal at the fundamental cavity-mode frequency (determined by the ring cavity length), which reflects the stability of mode-locking pulse train. We have found that the RO build-up time is inversely proportional to the average pump power while the RF power of the detected fundamental cavity mode (produced by the ring cavity) is proportional to the average pump power. A change in the duty cycle effectively leads the average pump power to vary, which in turn leads to changes in the transient response. The modulation frequency of the pump is rather related to the stability of the MLFL than its response time. Generally, the lower the modulation frequency, the more stable the mode-locked pulses generated in the fiber laser. Finally, the RO build-up time and, consequently, the pulse-generation time are highly sensitive to the state of polarization in the MLFL cavity.

  20. Multipulse dynamics of a passively mode-locked semiconductor laser with delayed optical feedback

    Science.gov (United States)

    Jaurigue, Lina; Krauskopf, Bernd; Lüdge, Kathy

    2017-11-01

    Passively mode-locked semiconductor lasers are compact, inexpensive sources of short light pulses of high repetition rates. In this work, we investigate the dynamics and bifurcations arising in such a device under the influence of time delayed optical feedback. This laser system is modelled by a system of delay differential equations, which includes delay terms associated with the laser cavity and feedback loop. We make use of specialised path continuation software for delay differential equations to analyse the regime of short feedback delays. Specifically, we consider how the dynamics and bifurcations depend on the pump current of the laser, the feedback strength, and the feedback delay time. We show that an important role is played by resonances between the mode-locking frequencies and the feedback delay time. We find feedback-induced harmonic mode locking and show that a mismatch between the fundamental frequency of the laser and that of the feedback cavity can lead to multi-pulse or quasiperiodic dynamics. The quasiperiodic dynamics exhibit a slow modulation, on the time scale of the gain recovery rate, which results from a beating with the frequency introduced in the associated torus bifurcations and leads to gain competition between multiple pulse trains within the laser cavity. Our results also have implications for the case of large feedback delay times, where a complete bifurcation analysis is not practical. Namely, for increasing delay, there is an ever-increasing degree of multistability between mode-locked solutions due to the frequency pulling effect.

  1. Direct generation of a 10 GHz 816 fs pulse train from an erbium-fiber soliton laser with asynchronous phase modulation.

    Science.gov (United States)

    Hsiang, Wei-Wei; Lin, Chian-Yu; Tien, Ming-Feng; Lai, Yinchieh

    2005-09-15

    By employing the technique of asynchronous mode locking, we have successfully demonstrated direct generation of stable 10 GHz 816 fs pulse trains with a supermode-suppression ratio >70 dB from a hybrid mode-locked Er-fiber laser. When the modulation frequency deviates from the cavity harmonic frequency by 15-40 kHz, stable femtosecond soliton pulses are formed. Our results demonstrate that asynchronous mode locking can act as an effective mechanism for achieving a shorter pulse width and for stabilizing high-repetition-rate pulse trains in soliton fiber lasers.

  2. Investigations of repetition rate stability of a mode-locked quantum dot semiconductor laser in an auxiliary optical fiber cavity

    DEFF Research Database (Denmark)

    Breuer, Stefan; Elsässer, Wolfgang; McInerney, J.G.

    2010-01-01

    We have investigated experimentally the pulse train (mode beating) stability of a monolithic mode-locked multi-section quantum-dot laser with an added passive auxiliary optical fiber cavity. Addition of the weakly coupled (¿ -24dB) cavity reduces the current-induced shift d¿/dI of the principal...

  3. Dispersion-managed semiconductor mode-locked ring laser.

    Science.gov (United States)

    Resan, Bojan; Archundia, Luis; Delfyett, Peter J; Alphonse, Gerard

    2003-08-01

    A novel breathing-mode external sigma-ring-cavity semiconductor mode-locked laser is developed. Intracavity pulse compression and stretching produce linearly chirped pulses with an asymmetric exponential temporal profile. External dispersion compensation reduces the pulse duration to 274 fs (within 10% of the bandwidth limit).

  4. Femtosecond Mode-locked Fiber Laser at 1 μm Via Optical Microfiber Dispersion Management.

    Science.gov (United States)

    Wang, Lizhen; Xu, Peizhen; Li, Yuhang; Han, Jize; Guo, Xin; Cui, Yudong; Liu, Xueming; Tong, Limin

    2018-03-16

    Mode-locked Yb-doped fiber lasers around 1 μm are attractive for high power applications and low noise pulse train generation. Mode-locked fiber lasers working in soliton and stretched-pulse regime outperform others in terms of the laser noise characteristics, mechanical stability and easy maintenance. However, conventional optical fibers always show a normal group velocity dispersion around 1 μm, leading to the inconvenience for necessary dispersion management. Here we show that optical microfibers having a large anomalous dispersion around 1 μm can be integrated into mode-locked Yb-doped fiber lasers with ultralow insertion loss down to -0.06 dB, enabling convenient dispersion management of the laser cavity. Besides, optical microfibers could also be adopted to spectrally broaden and to dechirp the ultrashort pulses outside the laser cavity, giving rise to a pulse duration of about 110 fs. We believe that this demonstration may facilitate all-fiber format high-performance ultrashort pulse generation at 1 μm and may find applications in precision measurements, large-scale facility synchronization and evanescent-field-based optical sensing.

  5. Passively mode-locked laser with an ultra-narrow spectral width

    Science.gov (United States)

    Kues, Michael; Reimer, Christian; Wetzel, Benjamin; Roztocki, Piotr; Little, Brent E.; Chu, Sai T.; Hansson, Tobias; Viktorov, Evgeny A.; Moss, David J.; Morandotti, Roberto

    2017-01-01

    Most mode-locking techniques introduced in the past focused mainly on increasing the spectral bandwidth to achieve ultrashort, sub-picosecond-long coherent light pulses. By contrast, less importance seemed to be given to mode-locked lasers generating Fourier-transform-limited nanosecond pulses, which feature the narrow spectral bandwidths required for applications in spectroscopy, the efficient excitation of molecules, sensing and quantum optics. Here, we demonstrate a passively mode-locked laser system that relies on simultaneous nested cavity filtering and cavity-enhanced nonlinear interactions within an integrated microring resonator. This allows us to produce optical pulses in the nanosecond regime (4.3 ns in duration), with an overall spectral bandwidth of 104.9 MHz—more than two orders of magnitude smaller than previous realizations. The very narrow bandwidth of our laser makes it possible to fully characterize its spectral properties in the radiofrequency domain using widely available GHz-bandwidth optoelectronic components. In turn, this characterization reveals the strong coherence of the generated pulse train.

  6. Stability of the mode-locking regime in tapered quantum-dot lasers

    Science.gov (United States)

    Bardella, P.; Drzewietzki, L.; Rossetti, M.; Weber, C.; Breuer, S.

    2018-02-01

    We study numerically and experimentally the role of the injection current and reverse bias voltage on the pulse stability of tapered, passively mode-locked, Quantum Dot (QD) lasers. By using a multi-section delayed differential equation and introducing in the model the QD inhomogenous broadening, we are able to predict the onset of leading and trailing edge instabilities in the emitted pulse trains and to identify specific trends of stability in dependence on the laser biasing conditions. The numerical results are confirmed experimentally trough amplitude and timing stability analysis of the pulses.

  7. Passively mode-locked diode-pumped Tm3+:YLF laser emitting at 1.91 µm using a GaAs-based SESAM

    Science.gov (United States)

    Tyazhev, A.; Soulard, R.; Godin, T.; Paris, M.; Brasse, G.; Doualan, J.-L.; Braud, A.; Moncorgé, R.; Laroche, M.; Camy, P.; Hideur, A.

    2018-04-01

    We report on a diode-pumped Tm:YLF laser passively mode-locked with an InGaAs saturable absorber. The laser emits a train of 31 ps pulses at a wavelength of 1.91 µm with a repetition rate of 94 MHz and a maximum average power of 95 mW. A sustained and robust mode-locking with a signal-to-noise ratio of ~70 dB is obtained even at high relative air humidity, making this system attractive for applications requiring ultra-short pulses in the spectral window just below 2 µm.

  8. Numerical simulation of passively mode-locked fiber laser based on semiconductor optical amplifier

    Science.gov (United States)

    Yang, Jingwen; Jia, Dongfang; Zhang, Zhongyuan; Chen, Jiong; Liu, Tonghui; Wang, Zhaoying; Yang, Tianxin

    2013-03-01

    Passively mode-locked fiber laser (MLFL) has been widely used in many applications, such as optical communication system, industrial production, information processing, laser weapons and medical equipment. And many efforts have been done for obtaining lasers with small size, simple structure and shorter pulses. In recent years, nonlinear polarization rotation (NPR) in semiconductor optical amplifier (SOA) has been studied and applied as a mode-locking mechanism. This kind of passively MLFL has faster operating speed and makes it easier to realize all-optical integration. In this paper, we had a thorough analysis of NPR effect in SOA. And we explained the principle of mode-locking by SOA and set up a numerical model for this mode-locking process. Besides we conducted a Matlab simulation of the mode-locking mechanism. We also analyzed results under different working conditions and several features of this mode-locking process are presented. Our simulation shows that: Firstly, initial pulse with the peak power exceeding certain threshold may be amplified and compressed, and stable mode-locking may be established. After about 25 round-trips, stable mode-locked pulse can be obtained which has peak power of 850mW and pulse-width of 780fs.Secondly, when the initial pulse-width is greater, narrowing process of pulse is sharper and it needs more round-trips to be stable. Lastly, the bias currents of SOA affect obviously the shape of mode-locked pulse and the mode-locked pulse with high peak power and narrow width can be obtained through adjusting reasonably the bias currents of SOA.

  9. Color center lasers passively mode locked by quantum wells

    International Nuclear Information System (INIS)

    Islam, M.N.; Soccolich, C.E.; Bar-Joseph, I.; Sauer, N.; Chang, T.Y.; Miller, B.I.

    1989-01-01

    This paper describes how, using multiple quantum well (MQW) saturable absorbers, the authors passively mode locked a NaCl color center laser to produce 275 fs transform-limited, pedestal-free pulses with as high as 3.7 kW peak power. The pulses are tunable from λ = 1.59 to 1.7 μm by choosing MQW's with different bandgaps. They shortened the output pulses from the laser to 25 fs using the technique of soliton compression in a fiber. The steady-state operation of the laser requires the combination of a fast saturable absorber and gain saturation. In addition to the NaCl laser, they passively mode locked a Tl 0 (1):KCl color center laser and produced -- 22 ps pulses. Although the 275 fs pulses from the NaCl laser are Gaussian, when broadened, the pulses acquire an asymmetric spectrum because of carrier-induced refractive index changes

  10. Dispersion engineering of mode-locked fibre lasers

    Science.gov (United States)

    Woodward, R. I.

    2018-03-01

    Mode-locked fibre lasers are important sources of ultrashort pulses, where stable pulse generation is achieved through a balance of periodic amplitude and phase evolutions. A range of distinct cavity pulse dynamics have been revealed, arising from the interplay between dispersion and nonlinearity in addition to dissipative processes such as filtering. This has led to the discovery of numerous novel operating regimes, offering significantly improved laser performance. In this Topical Review, we summarise the main steady-state pulse dynamics reported to date through cavity dispersion engineering, including average solitons, dispersion-managed solitons, dissipative solitons, giant-chirped pulses and similaritons. Characteristic features and the stabilisation mechanism of each regime are described, supported by numerical modelling, in addition to the typical performance and limitations. Opportunities for further pulse energy scaling are discussed, in addition to considering other recent advances including automated self-tuning cavities and fluoride-fibre-based mid-infrared mode-locked lasers.

  11. Various phenomena of self-mode-locked operation in optically pumped semiconductor lasers

    Science.gov (United States)

    Tsou, C. H.; Liang, H. C.; Huang, K. F.; Chen, Y. F.

    2017-02-01

    This work presents several optical experiments to investigate the phenomenon of self-mode locking (SML) in optically pumped semiconductor lasers (OPSLs). First of all, we systematically explore the influence of high-order transverse modes on the SML in an OPSL with a linear cavity. Experimental results reveal that the occurrence of SML can be assisted by the existence of the first high-order transverse mode, and the laser is operated in a well-behaved SML state with the existence of the TEM0,0 mode and the first high-order transverse mode. While more high-order transverse modes are excited, it is found that the pulse train is modulated by more beating frequencies of transverse modes. The temporal behavior becomes the random dynamics when too many high-order transverse modes are excited. We observe that the temporal trace exhibits an intermittent mode-locked state in the absence of high-order transverse modes. In addition to typical mode-locked pulses, we originally observe an intriguing phenomenon of SML in an OPSL related to the formation of bright-dark pulse pairs. We experimentally demonstrated that under the influence of the tiny reflection feedback, the phase locking between lasing longitudinal modes can be assisted to form bright-dark pulse pairs in the scale of round-trip time. A theoretical model based on the multiple reflections in a phase-locked multi-longitudinal-mode laser is developed to confirm the formation of bright-dark pulse pairs.

  12. Mode-Locked Multichromatic X-Rays in a Seeded Free-Electron Laser for Single-Shot X-Ray Spectroscopy

    Energy Technology Data Exchange (ETDEWEB)

    Xiang, Dao; Ding, Yuantao; Raubenheimer, Tor; Wu, Juhao; /SLAC

    2012-05-10

    We present the promise of generating gigawatt mode-locked multichromatic x rays in a seeded free-electron laser (FEL). We show that, by using a laser to imprint periodic modulation in electron beam phase space, a single-frequency coherent seed can be amplified and further translated to a mode-locked multichromatic output in an FEL. With this configuration the FEL output consists of a train of mode-locked ultrashort pulses which span a wide frequency gap with a series of equally spaced sharp lines. These gigawatt multichromatic x rays may potentially allow one to explore the structure and dynamics of a large number of atomic states simultaneously. The feasibility of generating mode-locked x rays ranging from carbon K edge ({approx}284 eV) to copper L{sub 3} edge ({approx}931 eV) is confirmed with numerical simulation using the realistic parameters of the linac coherent light source (LCLS) and LCLS-II. We anticipate that the mode-locked multichromatic x rays in FELs may open up new opportunities in x-ray spectroscopy (i.e. resonant inelastic x-ray scattering, time-resolved scattering and spectroscopy, etc.).

  13. 110 GHz hybrid mode-locked fiber laser with enhanced extinction ratio based on nonlinear silicon-on-insulator micro-ring-resonator (SOI MRR)

    Science.gov (United States)

    Liu, Yang; Hsu, Yung; Chow, Chi-Wai; Yang, Ling-Gang; Yeh, Chien-Hung; Lai, Yin-Chieh; Tsang, Hon-Ki

    2016-03-01

    We propose and experimentally demonstrate a new 110 GHz high-repetition-rate hybrid mode-locked fiber laser using a silicon-on-insulator microring-resonator (SOI MRR) acting as the optical nonlinear element and optical comb filter simultaneously. By incorporating a phase modulator (PM) that is electrically driven at a fraction of the harmonic frequency, an enhanced extinction ratio (ER) of the optical pulses can be produced. The ER of the optical pulse train increases from 3 dB to 10 dB. As the PM is only electrically driven by the signal at a fraction of the harmonic frequency, in this case 22 GHz (110 GHz/5 GHz), a low bandwidth PM and driving circuit can be used. The mode-locked pulse width and the 3 dB spectral bandwidth of the proposed mode-locked fiber laser are measured, showing that the optical pulses are nearly transform limited. Moreover, stability evaluation for an hour is performed, showing that the proposed laser can achieve stable mode-locking without the need for optical feedback or any other stabilization mechanism.

  14. On the mechanisms governing the repetition rate of mode-locked semiconductor lasers

    DEFF Research Database (Denmark)

    Mulet, Josep; Mørk, Jesper

    2004-01-01

    We investigate the mechanisms influencing the synchronization locking range of mode-locked lasers. We find that changes in repetition rates can be accomodated through a joint interplay of dispersion and pulse shaping effects.......We investigate the mechanisms influencing the synchronization locking range of mode-locked lasers. We find that changes in repetition rates can be accomodated through a joint interplay of dispersion and pulse shaping effects....

  15. Mode locked Nd3+ and Gd3+ co-doped calcium fluoride crystal laser at dual gain lines

    Science.gov (United States)

    Zhang, Feng; Wu, Yongjing; Liu, Jie; Pang, Siyuan; Ma, Fengkai; Jiang, Dapeng; Wu, Qinghui; Su, Liangbi

    2018-03-01

    Based on a novel disordered fluoride crystal-Nd3+ and Gd3+ co-doped CaF2, we demonstrate a dual-wavelength synchronously mode locked laser in a single cavity, for the first time. Two gain lines at 1064.2 nm and 1064.7 nm were synchronously mode locked by gain spectrum splitting method, corresponding to a 0.15 THz repetition rate. The mode locked laser shows a 6.5 ps separated pulse duration.

  16. Using graphene nano-particle embedded in photonic crystal fiber for evanescent wave mode-locking of fiber laser.

    Science.gov (United States)

    Lin, Yung-Hsiang; Yang, Chun-Yu; Liou, Jia-Hong; Yu, Chin-Ping; Lin, Gong-Ru

    2013-07-15

    A photonic crystal fiber (PCF) with high-quality graphene nano-particles uniformly dispersed in the hole cladding are demonstrated to passively mode-lock the erbium-doped fiber laser (EDFL) by evanescent-wave interaction. The few-layer graphene nano-particles are obtained by a stabilized electrochemical exfoliation at a threshold bias. These slowly and softly exfoliated graphene nano-particle exhibits an intense 2D band and an almost disappeared D band in the Raman scattering spectrum. The saturable phenomena of the extinction coefficient β in the cladding provides a loss modulation for the intracavity photon intensity by the evanescent-wave interaction. The evanescent-wave mode-locking scheme effectively enlarges the interaction length of saturable absorption with graphene nano-particle to provide an increasing transmittance ΔT of 5% and modulation depth of 13%. By comparing the core-wave and evanescent-wave mode-locking under the same linear transmittance, the transmittance of the graphene nano-particles on the end-face of SMF only enlarges from 0.54 to 0.578 with ΔT = 3.8% and the modulation depth of 10.8%. The evanescent wave interaction is found to be better than the traditional approach which confines the graphene nano-particles at the interface of two SMF patchcords. When enlarging the intra-cavity gain by simultaneously increasing the pumping current of 980-nm and 1480-nm pumping laser diodes (LDs) to 900 mA, the passively mode-locked EDFL shortens its pulsewidth to 650 fs and broadens its spectral linewidth to 3.92 nm. An extremely low carrier amplitude jitter (CAJ) of 1.2-1.6% is observed to confirm the stable EDFL pulse-train with the cladding graphene nano-particle based evanescent-wave mode-locking.

  17. Passive mode locking at harmonics of the free spectral range of the intracavity filter in a fiber ring laser.

    Science.gov (United States)

    Zhang, Shumin; Lu, Fuyun; Dong, Xinyong; Shum, Ping; Yang, Xiufeng; Zhou, Xiaoqun; Gong, Yandong; Lu, Chao

    2005-11-01

    We report the passive mode-locking at harmonics of the free spectral range (FSR) of the intracavity multi-channel filter in a fiber ring laser. The laser uses a sampled fiber Bragg grating (SFBG) with a free spectral range (FSR) of 0.8 nm, or 99 GHz at 1555 nm, and a length of highly nonlinear photonic crystal fiber with low and flat dispersion. Stable picosecond soliton pulse trains with twofold to sevenfold enhancement in the repetition rate, relative to the FSR of the SFBG, have been achieved. The passive mode-locking mechanism that is at play in this laser relies on a dissipative four-wave mixing process and switching of repetition rate is realized simply by adjustment of the intracavity polarization controllers.

  18. Commercial mode-locked vertical external cavity surface emitting lasers

    Science.gov (United States)

    Lubeigt, Walter; Bialkowski, Bartlomiej; Lin, Jipeng; Head, C. Robin; Hempler, Nils; Maker, Gareth T.; Malcolm, Graeme P. A.

    2017-02-01

    In recent years, M Squared Lasers have successfully commercialized a range of mode-locked vertical external cavity surface emitting lasers (VECSELs) operating between 920-1050nm and producing picosecond-range pulses with average powers above 1W at pulse repetition frequencies (PRF) of 200MHz. These laser products offer a low-cost, easy-to-use and maintenance-free tool for the growing market of nonlinear microscopy. However, in order to present a credible alternative to ultrafast Ti-sapphire lasers, pulse durations below 200fs are required. In the last year, efforts have been directed to reduce the pulse duration of the Dragonfly laser system to below 200fs with a target average power above 1W at a PRF of 200MHz. This paper will describe and discuss the latest efforts undertaken to approach these targets in a laser system operating at 990nm. The relatively low PRF operation of Dragonfly lasers represents a challenging requirement for mode-locked VECSELs due to the very short upper state carrier lifetime, on the order of a few nanoseconds, which can lead to double pulsing behavior in longer cavities as the time between consecutive pulses is increased. Most notably, the design of the Dragonfly VECSEL cavity was considerably modified and the laser system extended with a nonlinear pulse stretcher and an additional compression stage. The improved Dragonfly laser system achieved pulse duration as short as 130fs with an average power of 0.85W.

  19. Mode-locked terahertz quantum cascade laser by direct phase synchronization

    International Nuclear Information System (INIS)

    Maussang, K.; Maysonnave, J.; Jukam, N.; Freeman, J. R.; Cavalié, P.; Dhillon, S. S.; Tignon, J.; Khanna, S. P.; Linfield, E. H.; Davies, A. G.; Beere, H. E.; Ritchie, D. A.

    2013-01-01

    Mode-locking of a terahertz quantum cascade laser is achieved using multimode injection seeding. Contrary to standard methods that rely on gain modulation, here a fixed phase relationship is directly imprinted to the laser modes. In this work, we demonstrate the generation of 9 ps phase mode-locked pulses around 2.75 THz. A direct measurement of the emitted field phase shows that it results from the phase of the initial injection

  20. Deep-red semiconductor monolithic mode-locked lasers

    Energy Technology Data Exchange (ETDEWEB)

    Kong, L.; Bajek, D.; White, S. E.; Forrest, A. F.; Cataluna, M. A., E-mail: m.a.cataluna@dundee.ac.uk [School of Engineering, Physics and Mathematics, University of Dundee, Dundee DD1 4HN (United Kingdom); Wang, H. L.; Pan, J. Q. [Institute of Semiconductors, Chinese Academy of Sciences, Beijing 100083 (China); Wang, X. L.; Cui, B. F. [Key Laboratory of Opto-electronics Technology, Ministry of Education, Beijing University of Technology, Beijing 100124 (China); Ding, Y. [School of Engineering, Physics and Mathematics, University of Dundee, Dundee DD1 4HN (United Kingdom); School of Engineering, University of Glasgow, Glasgow G12 8LT (United Kingdom)

    2014-12-01

    A deep-red semiconductor monolithic mode-locked laser is demonstrated. Multi-section laser diodes based on an AlGaAs multi-quantum-well structure were passively mode-locked, enabling the generation of picosecond optical pulses at 752 nm, at pulse repetition rates of 19.37 GHz. An investigation of the dependence of the pulse duration as a function of reverse bias revealed a predominantly exponential decay trend of the pulse duration, varying from 10.5 ps down to 3.5 ps, which can be associated with the concomitant reduction of absorption recovery time with increasing applied field. A 30-MHz-tunability of the pulse repetition rate with bias conditions is also reported. The demonstration of such a compact, efficient and versatile ultrafast laser in this spectral region paves the way for its deployment in a wide range of applications such as biomedical microscopy, pulsed terahertz generation as well as microwave and millimeter-wave generation, with further impact on sensing, imaging and optical communications.

  1. Widely tunable all-fiber SESAM mode-locked Ytterbium laser with a linear cavity

    Science.gov (United States)

    Zou, Feng; Wang, Zhaokun; Wang, Ziwei; Bai, Yang; Li, Qiurui; Zhou, Jun

    2017-07-01

    We present a widely tunable all-fiber mode-locked laser based on semiconductor saturable absorber mirror (SESAM) with a linear cavity design. An easy-to-use tunable bandpass filter based on thin film cavity technology is employed to tune the wavelength. By tuning the filter and adjusting the polarization controller, mode-locked operation can be achieved over the range of 1023 nm-1060 nm. With the polarization controller settled, mode-locked operation can be preserved and the wavelength can be continuously tuned from 1030 nm to 1053 nm. At 1030 nm, the laser delivers 9.6 mw average output power with 15.4 ps 10.96 MHz pulses at fundamental mode-locked operation.

  2. Numerical investigations on the performance of external-cavity mode-locked semiconductor lasers

    DEFF Research Database (Denmark)

    Mulet, Josep; Mørk, Jesper

    2004-01-01

    The performance of an external-cavity mode-locked semiconductor laser is analyzed theoretically and numerically. Passive mode-locking is described using a fully-distributed time-domain model including fast effects, spectral hole burning and carrier heating. We provide optimization rules in order...... to improve the mode-locking performance, such as reducing the pulsewidth and time-bandwidth product as much as possible. Timing jitter is determined by means of extensive numerical simulations of the model, demontrating that an external modulation is required in order to maintain moderate timing......-jitter and phase-noise levels at low frequencies. The effect of the driving conditions is investigated in order to achieve short pulses and low timing jitter. Our results are in qualitative agreement with reported experiments and predictions obtained from the master equation for mode-locking....

  3. Quasi-continuously pumped passively mode-locked 2.4% doped Nd:YAG oscillator-amplifier system in a bounce geometry

    Science.gov (United States)

    Jelínek, Michal; Kubecek, Vaclav; Cech, Miroslav; Hirsl, Petr

    2010-02-01

    We report on oscillator-amplifier system based on two highly doped 2.4 at. % crystalline Czochralski grown Nd:YAG crystals in a diode pumped bounce geometry configuration under quasi-continuous pumping. The oscillator was passively mode-locked by the semiconductor saturable absorber in transmission mode. The output pulse train consisted of 5 pulses with total energy of 270 μJ and pulse duration of 75 ps. The output train from the oscillator was amplified to the energy of 1 mJ by single pass amplifier.

  4. Semiconductor Mode-Locked Lasers for Optical Communication Systems

    DEFF Research Database (Denmark)

    Yvind, Kresten

    2003-01-01

    The thesis deals with the design and fabrication of semiconductor mode-locked lasers for use in optical communication systems. The properties of pulse sources and characterization methods are described as well as requirements for application in communication systems. Especially, the importance of......, and ways to reduce high-frequency jitter is discussed. The main result of the thesis is a new design of the epitaxial structure that both enables simplified fabrication and improves the properties of monolithic lasers. 40 GHz monolithic lasers with record low jitter and high power is presented as well...

  5. Mode-locked Pr3+-doped silica fiber laser with an external cavity

    DEFF Research Database (Denmark)

    Shi, Yuan; Poulsen, Christian; Sejka, Milan

    1994-01-01

    We present a Pr3+-doped silica-based fiber laser mode-locked by using a linear external cavity with a vibrating mirror. Stable laser pulses with a FWHM of less than 44 ps, peak power greater than 9 W, and repetition rate up to 100 MHz are obtained. The pulse width versus cavity mismatch ΔL and pump...

  6. Optical self-injection mode-locking of semiconductor optical amplifier fiber ring with electro-absorption modulation—fundamentals and applications

    Science.gov (United States)

    Chi, Yu-Chieh; Lin, Gong-Ru

    2013-04-01

    The optical self-injection mode-locking of a semiconductor optical amplifier incorporated fiber ring laser (SOAFL) with spectrally sliced multi-channel carriers is demonstrated for applications. The synthesizer-free SOAFL pulse-train is delivered by optical injection mode-locking with a 10 GHz self-pulsed electro-absorption modulator (EAM). Such a coupled optical and electronic resonator architecture facilitates a self-feedback oscillation with a higher Q-factor and lower phase/intensity noises when compared with conventional approaches. The theoretical model of such an injection-mode-locking SOAFL is derived to improve the self-pulsating performance of the optical return-to-zero (RZ) carrier, thus providing optimized pulsewidth, pulse extinction ratio, effective Q-factor, frequency variation and timing jitter of 11.4 ps, 9.1 dB, 4 × 105, pulsed carrier is also employed for the application in a 10 Gbit s-1 bi-directional WDM transmission network with down-stream RZ binary phase-shift keying (RZ-BPSK) and up-stream re-modulated RZ on-off-keying (RZ-OOK) formats. Under BPSK/OOK bi-directional data transmission, the self-pulsed harmonic mode-locking SOAFL simultaneously provides four to six WDM channels for down-stream RZ-BPSK and up-stream RZ-OOK formats with receiving sensitivities of -17 and -15.2 dBm at a bit error rate of 10-9, respectively.

  7. Theory of Passively Mode-Locked Photonic Crystal Semiconductor Lasers

    DEFF Research Database (Denmark)

    Heuck, Mikkel; Blaaberg, Søren; Mørk, Jesper

    2010-01-01

    We report the first theoretical investigation of passive mode-locking in photonic crystal mode-locked lasers. Related work has investigated coupled-resonator-optical-waveguide structures in the regime of active mode-locking [Opt. Express 13, 4539-4553 (2005)]. An extensive numerical investigation...

  8. Novel design of low-jitter 10 GHz all-active monolithic mode-locked lasers

    DEFF Research Database (Denmark)

    Larsson, David; Yvind, Kresten; Christiansen, Lotte Jin

    2004-01-01

    Using a novel design, we have fabricated 10 GHz all-active monolithic mode-locked semiconductor lasers that generate 1.4 ps pulses with record-low timing jitter. The dynamical properties of lasers with 1 and 2 QWs are compared.......Using a novel design, we have fabricated 10 GHz all-active monolithic mode-locked semiconductor lasers that generate 1.4 ps pulses with record-low timing jitter. The dynamical properties of lasers with 1 and 2 QWs are compared....

  9. Control of fibre laser mode-locking by narrow-band Bragg gratings

    International Nuclear Information System (INIS)

    Laegsgaard, J

    2008-01-01

    The use of narrow-band high-reflectivity fibre Bragg gratings (FBGs) as end mirrors in a fibre laser cavity with passive mode-locking provided by a semiconductor saturable absorber mirror (SESAM) is investigated numerically. The FBG is found to control the energy range of stable mode-locking, which may be shifted far outside the regime of SESAM saturation by a suitable choice of FBG and cavity length. The pulse shape is controlled by the combined effects of FBG dispersion and self-phase modulation in the fibres, and a few ps pulses can be obtained with standard uniform FBGs

  10. Low jitter and high power all-active mode-locked lasers

    DEFF Research Database (Denmark)

    Yvind, Kresten; Larsson, David; Christiansen, Lotte Jin

    2003-01-01

    A novel epitaxial design leading to low loss and low gain saturation improves the properties of 40 GHz mode-locked lasers. We obtain 2.8 ps nearly chirp free pulses with 228 fs jitter and -coupled power of 7 mW.......A novel epitaxial design leading to low loss and low gain saturation improves the properties of 40 GHz mode-locked lasers. We obtain 2.8 ps nearly chirp free pulses with 228 fs jitter and -coupled power of 7 mW....

  11. Low jitter and high power all-active mode-locked lasers

    DEFF Research Database (Denmark)

    Yvind, Kresten; Larsson, David; Christiansen, Lotte Jin

    2003-01-01

    A novel epitaxial design leading to low loss and low gain saturation improves the properties of 40 GHz mode-locked lasers. We obtain 2.8 ps nearly chirp free pulses with 228 fs jitter and fiber-coupled power of 7 mW.......A novel epitaxial design leading to low loss and low gain saturation improves the properties of 40 GHz mode-locked lasers. We obtain 2.8 ps nearly chirp free pulses with 228 fs jitter and fiber-coupled power of 7 mW....

  12. Passive, active, and hybrid mode-locking in a self-optimized ultrafast diode laser

    Science.gov (United States)

    Alloush, M. Ali; Pilny, Rouven H.; Brenner, Carsten; Klehr, Andreas; Knigge, Andrea; Tränkle, Günther; Hofmann, Martin R.

    2018-02-01

    Semiconductor lasers are promising sources for generating ultrashort pulses. They are directly electrically pumped, allow for a compact design, and therefore they are cost-effective alternatives to established solid-state systems. Additionally, their emission wavelength depends on the bandgap which can be tuned by changing the semiconductor materials. Theoretically, the obtained pulse width can be few tens of femtoseconds. However, the generated pulses are typically in the range of several hundred femtoseconds only. Recently, it was shown that by implementing a spatial light modulator (SLM) for phase and amplitude control inside the resonator the optical bandwidth can be optimized. Consequently, by using an external pulse compressor shorter pulses can be obtained. We present a Fourier-Transform-External-Cavity setup which utilizes an ultrafast edge-emitting diode laser. The used InGaAsP diode is 1 mm long and emits at a center wavelength of 850 nm. We investigate the best conditions for passive, active and hybrid mode-locking operation using the method of self-adaptive pulse shaping. For passive mode-locking, the bandwidth is increased from 2.34 nm to 7.2 nm and ultrashort pulses with a pulse width of 216 fs are achieved after external pulse compression. For active and hybrid mode-locking, we also increased the bandwidth. It is increased from 0.26 nm to 5.06 nm for active mode-locking and from 3.21 nm to 8.7 nm for hybrid mode-locking. As the pulse width is strongly correlated with the bandwidth of the laser, we expect further reduction in the pulse duration by increasing the bandwidth.

  13. Mode-locking via dissipative Faraday instability.

    Science.gov (United States)

    Tarasov, Nikita; Perego, Auro M; Churkin, Dmitry V; Staliunas, Kestutis; Turitsyn, Sergei K

    2016-08-09

    Emergence of coherent structures and patterns at the nonlinear stage of modulation instability of a uniform state is an inherent feature of many biological, physical and engineering systems. There are several well-studied classical modulation instabilities, such as Benjamin-Feir, Turing and Faraday instability, which play a critical role in the self-organization of energy and matter in non-equilibrium physical, chemical and biological systems. Here we experimentally demonstrate the dissipative Faraday instability induced by spatially periodic zig-zag modulation of a dissipative parameter of the system-spectrally dependent losses-achieving generation of temporal patterns and high-harmonic mode-locking in a fibre laser. We demonstrate features of this instability that distinguish it from both the Benjamin-Feir and the purely dispersive Faraday instability. Our results open the possibilities for new designs of mode-locked lasers and can be extended to other fields of physics and engineering.

  14. Mode-locked Ti:sapphire laser oscillators pumped by wavelength-multiplexed laser diodes

    Science.gov (United States)

    Sugiyama, Naoto; Tanaka, Hiroki; Kannari, Fumihiko

    2018-05-01

    We directly pumped a Ti:sapphire laser by combining 478 and 520 nm laser diodes to prevent the effect of absorption loss induced by the pump laser of shorter wavelengths (∼450 nm). We obtain a continuous-wave output power of 660 mW at a total incident pump power of 3.15 W. We demonstrate mode locking using a semiconductor saturable absorber mirror, and 126 fs pulses were obtained at a repetition rate of 192 MHz. At the maximum pump power, the average output power is 315 mW. Shorter mode-locked pulses of 42 and 48 fs were respectively achieved by Kerr-lens mode locking with average output powers of 280 and 360 mW at a repetition rate of 117 MHz.

  15. The Proper Orthogonal Decomposition for Dimensionality Reduction in Mode-Locked Lasers and Optical Systems

    Directory of Open Access Journals (Sweden)

    Eli Shlizerman

    2012-01-01

    energy delivered per pulse. Managing the nonlinear penalties in the cavity becomes crucial for increasing the energy and suppressing the multipulsing instability. A proper orthogonal decomposition (POD allows for the reduction of governing equations of a mode-locked laser onto a low-dimensional space. The resulting reduced system is able to capture correctly the experimentally observed pulse transitions. Analysis of these models is used to explain the sequence of bifurcations that are responsible for the multipulsing instability in the master mode-locking and the waveguide array mode-locking models. As a result, the POD reduction allows for a simple and efficient way to characterize and optimize the cavity parameters for achieving maximal energy output.

  16. Harmonic Mode-Locked Fiber Laser based on Photonic Crystal Fiber Filled with Topological Insulator Solution

    Directory of Open Access Journals (Sweden)

    Yu-Shan Chen

    2015-04-01

    Full Text Available We reported that the photonic crystal fiber (PCF filled with TI:Bi2Te3 nanosheets solution could act as an effective saturable absorber (SA. Employing this TI-PCF SA device; we constructed an ytterbium-doped all-fiber laser oscillator and achieved the evanescent wave mode-locking operation. Due to the large cavity dispersion; the fundamental mode-locking pulse had the large full width at half maximum (FWHM of 2.33 ns with the repetition rate of ~1.11 MHz; and the radio frequency (RF spectrum with signal-to-noise ratio (SNR of 61 dB. In addition; the transition dynamics from a bunched state of pulses to harmonic mode-locking (HML was also observed; which was up to 26th order.

  17. Three-dimensional graphene based passively mode-locked fiber laser.

    Science.gov (United States)

    Yang, Y; Loeblein, M; Tsang, S H; Chow, K K; Teo, E H T

    2014-12-15

    We present an all-fiber passively mode-locked fiber laser incorporating three-dimensional (3D) graphene as a saturable absorber (SA) for the first time to the best of our knowledge. The 3D graphene is synthesized by template-directed chemical vapor deposition (CVD). The SA is then simply formed by sandwiching the freestanding 3D graphene between two conventional fiber connectors without any deposition process. It is demonstrated that such 3D graphene based SA is capable to produce high quality mode-locked pulses. A passively mode-locked fiber laser is constructed and stable output pulses with a fundamental repetition rate of ~9.9 MHz and a pulse width of ~1 ps are generated from the fiber laser. The average output power of the laser is ~10.5 mW while the output pulse is operating at single pulse region. The results imply that the freestanding 3D graphene can be applied as an effective saturable absorption material for passively mode-locked lasers.

  18. Material Engineering for Monolithic Semiconductor Mode-Locked Lasers

    DEFF Research Database (Denmark)

    Kulkova, Irina

    This thesis is devoted to the materials engineering for semiconductor monolithic passively mode-locked lasers (MLLs) as a compact energy-efficient source of ultrashort optical pulses. Up to the present day, the achievement of low-noise sub-picosecond pulse generation has remained a challenge...... application in MLLs. Improved QW laser performance was demonstrated using the asymmetric barrier layer approach. The analysis of the gain characteristics showed that the high population inversion beneficial for noise reduction cannot be achieved for 10 GHz QW MLLs and would have required lowering the modal....... This work has considered the role of the combined ultrafast gain and absorption dynamics in MLLs as a main factor limiting laser performance. An independent optimization of MLL amplifier and saturable absorber active materials was performed. Two promising approaches were considered: quantum dot (QD...

  19. Deep learning and model predictive control for self-tuning mode-locked lasers

    Science.gov (United States)

    Baumeister, Thomas; Brunton, Steven L.; Nathan Kutz, J.

    2018-03-01

    Self-tuning optical systems are of growing importance in technological applications such as mode-locked fiber lasers. Such self-tuning paradigms require {\\em intelligent} algorithms capable of inferring approximate models of the underlying physics and discovering appropriate control laws in order to maintain robust performance for a given objective. In this work, we demonstrate the first integration of a {\\em deep learning} (DL) architecture with {\\em model predictive control} (MPC) in order to self-tune a mode-locked fiber laser. Not only can our DL-MPC algorithmic architecture approximate the unknown fiber birefringence, it also builds a dynamical model of the laser and appropriate control law for maintaining robust, high-energy pulses despite a stochastically drifting birefringence. We demonstrate the effectiveness of this method on a fiber laser which is mode-locked by nonlinear polarization rotation. The method advocated can be broadly applied to a variety of optical systems that require robust controllers.

  20. Low-jitter and high-power 40 GHz all-active mode-locked lasers

    DEFF Research Database (Denmark)

    Yvind, Kresten; Larsson, David; Christiansen, Lotte Jin

    2004-01-01

    A novel design strategy for the epitaxial structure of monolithic mode-locked semiconductor lasers is presented. Using an all-active design, we fabricate 40-GHz lasers generating 2.8-ps almost chirp-free pulses with record low high-frequency jitter and more than 7-mW fiber coupled output power....

  1. Mode-locked 1.5 micrometers semiconductor optical amplifier fiber ring

    DEFF Research Database (Denmark)

    Pedersen, Niels V.; Jakobsen, Kaj Bjarne; Vaa, Michael

    1996-01-01

    The dynamics of a mode-locked SOA fiber ring are investigated experimentally and numerically. Generation of near transform-limited (time-bandwidth product=0.7) 1.5 μm 54 ps FWHM pulses with a peak power of 2.8 mW at a repetition rate of 960 MHz is demonstrated experimentally. The experimental...

  2. Tunable mode-locked semiconductor laser with Bragg mirror external cavity

    DEFF Research Database (Denmark)

    Yvind, Kresten; Jørgensen, T.; Birkedal, Dan

    2002-01-01

    We present a simplified design for a wavelength tunable external cavity mode-locked laser by employing a wedged GaAs/AlGaAs Bragg mirror. The device emits 4-6 ps pulses at 10 GHz and is tunable over 15 nm. Although, in the present configuration, tunability is limited to 15 nm, however, we have...

  3. Mode-Locked 1.5 um Semiconductor Optical Fiber Ring

    DEFF Research Database (Denmark)

    Pedersen, Niels Vagn; Jakobsen, Kaj Bjarne; Vaa, Michael

    1996-01-01

    The dynamics of a mode-locked SOA fiber ring are investigated experimentally and numerically. Generation of near transform-limited (time-bandwidth product = 0.7) 1.5 um 54 ps FWHM pulses with a peak power of 2.8 mW at a repetition rate of 960 MHz is demonstrated experimentally. The experimental...

  4. Time-resolved reconstruction of dynamical pulse trains using multiheterodyne detection

    Science.gov (United States)

    Butler, T.; Tykalewicz, B.; Goulding, D.; Kelleher, B.; Huyet, Guillaume; Hegarty, S. P.

    2014-05-01

    A technique has been developed for the measurement of pulse trains demonstrating a dynamical behaviour (i.e. not ideally periodic). Existing techniques in this area (e.g. FROG, SPIDER or other heterodyne methods) require very stable pulse trains, or large averaging times, and so are limited when applied to even slowly varying pulse trains. The technique presented involves mixing the comb under test (CUT) with a reference optical frequency comb (OFC) which has a known spectral intensity profile. Mixing these signals on a photodiode results in a series of radio frequency (RF) beat tones. The phase properties of these beat tones can be used to measure the spectral phase between adjacent modes in the CUT, allowing the full complex spectrum of the CUT to be measured simultaneously with one single real time oscilloscope acquisition. With the spectral properties of the comb known, the pulse train can be reconstructed in the temporal domain. By applying this technique to very small sections of the beating signal ( tens of nanoseconds), a time resolved picture of the pulse train behaviour can be obtained. Dynamic signals generated in a LiNbO3 modulator driven by a modulated RF signal have been measured. This technique is well suited to studying the combs produced by mode-locked semiconductor lasers. Quantum dot mode-locked laser combs can be characterised, and pulse train instabilities measured.

  5. Mathematical solutions of rate equations of a laser-diode end-pumped passively Q-switched and mode locked Nd-laser with Cr4+:YAG polarized saturable absorber

    International Nuclear Information System (INIS)

    Abdul Ghani, B.; Hammadi, M.

    2012-01-01

    The intracavity frequency-doubling (IFD) of a simultaneous passively Q-switched mode-locked diode-pumped Nd 3 + - laser is studied with a polarized isotropic Cr 4 +: YAG saturable absorber. A general recurrence formula for the mode-locked pulses under the Q-switched envelope at fundamental wavelength has been reconstructed in order to analyze the temporal shape behavior of a single Q-switched envelope with mode-locking pulse trains. This formula has been derived taking into account the impact of the IFD and polarized Cr 4 +: YAG saturable absorber.The presented mathematical model describes the self-induced anisotropy appeared in the polarized Cr 4 +: YAG in the nonlinear stage of the giant pulse formation. For the anisotropic Nd 3 +: YVO 4 active medium, the generated polarized waves are assumed to be fixed through the lasing cycle. Besides, the maximum absorber initial transmission and the minimum mirror reflectivity values have been determined from the second threshold criterion. The calculated numerical results demonstrate the impact of the variation of the input laser parameters (rotational angle of the polarized crystal, absorber initial transmission and the output mirror reflectivity) on the characteristics of the output laser pulse (SH peak power, pulse width, pulse duration and shift pulse position of central mode). The calculated numerical results in this work is in good qualitative and quantitative agreement with the available experimental data reported in the references. (author)

  6. High brightness photonic band crystal semiconductor lasers in the passive mode locking regime

    Energy Technology Data Exchange (ETDEWEB)

    Rosales, R.; Kalosha, V. P.; Miah, M. J.; Bimberg, D. [Institut für Festkörperphysik, Technische Universität Berlin, Hardenbergstrasse 36, 10623 Berlin (Germany); Posilović, K. [Institut für Festkörperphysik, Technische Universität Berlin, Hardenbergstrasse 36, 10623 Berlin (Germany); PBC Lasers GmbH, Hardenbergstrasse 36, 10623 Berlin (Germany); Pohl, J.; Weyers, M. [Ferdinand-Braun-Institut, Leibniz-Institut für Höchstfrequenztechnik, Gustav-Kirchhoff-Str. 4, Berlin 12489 (Germany)

    2014-10-20

    High brightness photonic band crystal lasers in the passive mode locking regime are presented. Optical pulses with peak power of 3 W and peak brightness of about 180 MW cm{sup −2} sr{sup −1} are obtained on a 5 GHz device exhibiting 15 ps pulses and a very low beam divergence in both the vertical and horizontal directions.

  7. High brightness photonic band crystal semiconductor lasers in the passive mode locking regime

    International Nuclear Information System (INIS)

    Rosales, R.; Kalosha, V. P.; Miah, M. J.; Bimberg, D.; Posilović, K.; Pohl, J.; Weyers, M.

    2014-01-01

    High brightness photonic band crystal lasers in the passive mode locking regime are presented. Optical pulses with peak power of 3 W and peak brightness of about 180 MW cm −2  sr −1 are obtained on a 5 GHz device exhibiting 15 ps pulses and a very low beam divergence in both the vertical and horizontal directions.

  8. Harmonic mode-locking and sub-round-trip time nonlinear dynamics of electro-optically controlled solid state laser

    Science.gov (United States)

    Gorbunkov, M. V.; Maslova, Yu Ya; Petukhov, V. A.; Semenov, M. A.; Shabalin, Yu V.; Tunkin, V. G.

    2018-03-01

    Harmonic mode-locking in a solid state laser due to optoelectronic control is studied numerically on the basis of two methods. The first one is detailed numeric simulation taking into account laser radiation fine time structure. It is shown that optimally chosen feedback delay leads to self-started mode-locking with generation of desired number of pulses in the laser cavity. The second method is based on discrete maps for short laser pulse energy. Both methods show that the application of combination of positive and negative feedback loops allows to reduce the period of regular nonlinear dynamics down to a fraction of a laser cavity round trip time.

  9. Combination of Transverse Mode Selection and Active Longitudinal Mode-Locking of Broad Area Semiconductor Lasers

    Directory of Open Access Journals (Sweden)

    Christoph Doering

    2014-01-01

    Full Text Available Experimental results of the combination of transverse mode selection and active mode-locking with anti-reflection-coated broad area lasers (BALs are presented. The BALs are subject to feedback from a free-space external Fourier-optical 4f-setup with a reflective spatial frequency filter in the Fourier-plane for transverse mode selection. Driving the BALs with a high frequency modulated pump current above threshold active longitudinal mode-locking is achieved. Pulse durations as low as 88 ps are obtained, while the Gaussian-like fundamental or a higher order transverse mode up to mode number 5 is selected on purpose. Pulse duration and shape are nearly independent of the selected transverse mode.

  10. Active-passively mode-locked dye laser for diagnosis of laser-produced plasmas

    International Nuclear Information System (INIS)

    Teng, Y.L.; Fedosejevs, R.; Sigel, R.

    1981-03-01

    In this report an active-passively mode-locked, flashlamp-pumped dye laser for diagnosis of laser-produced plasmas is described. This dye laser system used as a pulsed light source for high-speed photography of laser-target experiments was synchronized to the ASTERIX III iodine laser pulse with better than 100 ps accuracy. The single pulse energy was 10 μJ, pulse duration less than 10 ps. In 111 shots clear shadowgrams were obtained during a total of 151 target shots, i.e. the system worked well in 74% of the shots. (orig.)

  11. Observation of Coexisting Dissipative Solitons in a Mode-Locked Fiber Laser.

    Science.gov (United States)

    Bao, Chengying; Chang, Wonkeun; Yang, Changxi; Akhmediev, Nail; Cundiff, Steven T

    2015-12-18

    We show, experimentally and numerically, that a mode-locked fiber laser can operate in a regime where two dissipative soliton solutions coexist and the laser will periodically switch between the solutions. The two dissipative solitons differ in their pulse energy and spectrum. The switching can be controlled by an external perturbation and triggered even when switching does not occur spontaneously. Numerical simulations unveil the importance of the double-minima loss spectrum and nonlinear gain to the switching dynamics.

  12. All-fiber nonlinearity- and dispersion-managed dissipative soliton nanotube mode-locked laser

    Energy Technology Data Exchange (ETDEWEB)

    Zhang, Z. [Department of Physics, Bilkent University, 06800 Ankara (Turkey); Nanjing University of Posts and Communications, Nanjing 210003 (China); Popa, D., E-mail: dp387@cam.ac.uk; Wittwer, V. J.; Milana, S.; Hasan, T.; Jiang, Z.; Ferrari, A. C. [Cambridge Graphene Centre, University of Cambridge, Cambridge CB3 0FA (United Kingdom); Ilday, F. Ö. [Department of Physics, Bilkent University, 06800 Ankara (Turkey); Department of Electrical and Electronics Engineering, Bilkent University, 06800 Ankara (Turkey)

    2015-12-14

    We report dissipative soliton generation from an Yb-doped all-fiber nonlinearity- and dispersion-managed nanotube mode-locked laser. A simple all-fiber ring cavity exploits a photonic crystal fiber for both nonlinearity enhancement and dispersion compensation. The laser generates stable dissipative solitons with large linear chirp in the net normal dispersion regime. Pulses that are 8.7 ps long are externally compressed to 118 fs, outperforming current nanotube-based Yb-doped fiber laser designs.

  13. Mode-Locked Semiconductor Lasers for Optical Communication Systems

    DEFF Research Database (Denmark)

    Yvind, Kresten; Larsson, David; Oxenløwe, Leif Katsuo

    2005-01-01

    We present investigations on 10 and 40 GHz monolithic mode-locked lasers for applications in optical communications systems. New all-active lasers with one to three quantum wells have been designed, fabricated and characterized.......We present investigations on 10 and 40 GHz monolithic mode-locked lasers for applications in optical communications systems. New all-active lasers with one to three quantum wells have been designed, fabricated and characterized....

  14. Passively mode-locked Nd:YVO4 laser operating at 1073 nm and 1085 nm

    Science.gov (United States)

    Waritanant, Tanant; Major, Arkady

    2018-02-01

    A passively mode-locked Nd:YVO4 laser operating at 1073 nm and 1085 nm was demonstrated with an intracavity birefringent filter as the wavelength selecting element. The average output powers achieved were 2.17 W and 2.18 W with optical-to-optical efficiency of 19.6% and 19.7%, respectively. The slope efficiencies were more than 31% at both output wavelengths. The pulse durations at the highest average output power were 10.3 ps and 8.4 ps, respectively. We believe that this is the first report of mode locking of a Nd:YVO4 laser operating at 1073 nm or 1085 nm lines.

  15. Dark solitons of the power-energy saturation model: application to mode-locked lasers

    International Nuclear Information System (INIS)

    Ablowitz, M J; Nixon, S D; Horikis, T P; Frantzeskakis, D J

    2013-01-01

    The generation and dynamics of dark solitons in mode-locked lasers is studied within the framework of a nonlinear Schrödinger equation which incorporates power-saturated loss, as well as energy-saturated gain and filtering. Mode-locking into single dark solitons and multiple dark pulses are found by employing different descriptions for the energy and power of the system defined over unbounded and periodic (ring laser) systems. Treating the loss, gain and filtering terms as perturbations, it is shown that these terms induce an expanding shelf around the soliton. The dark soliton dynamics are studied analytically by means of a perturbation method that takes into regard the emergence of the shelves and reveals their importance. (paper)

  16. Scalar-vector soliton fiber laser mode-locked by nonlinear polarization rotation.

    Science.gov (United States)

    Wu, Zhichao; Liu, Deming; Fu, Songnian; Li, Lei; Tang, Ming; Zhao, Luming

    2016-08-08

    We report a passively mode-locked fiber laser by nonlinear polarization rotation (NPR), where both vector and scalar soliton can co-exist within the laser cavity. The mode-locked pulse evolves as a vector soliton in the strong birefringent segment and is transformed into a regular scalar soliton after the polarizer within the laser cavity. The existence of solutions in a polarization-dependent cavity comprising a periodic combination of two distinct nonlinear waves is first demonstrated and likely to be applicable to various other nonlinear systems. For very large local birefringence, our laser approaches the operation regime of vector soliton lasers, while it approaches scalar soliton fiber lasers under the condition of very small birefringence.

  17. Fabrication and Characterisation of Low-noise Monolithic Mode-locked Lasers

    DEFF Research Database (Denmark)

    Larsson, David

    2007-01-01

    This thesis deals with the fabrication and characterisation of monolithic semiconductor mode-locked lasers for use in optical communication systems. Other foreseeable applications may be as sources in microwave photonics and optical sampling. The thesis also deals with the design and fabrication...... of intracavity monolithically integrated filters. The common dnominator among the diffrent parts of the thesis is how to achieve and measure the lowest possible noise. Achieving low noise has been pinpointed as one of the most important and difficult challenges for semiconductor mode-locked lasers. The main...... result of this thesis are a fabrication process of a monolithic and deeply etched distributed Bragg reflector and a characterisation system for measurement of quantum limitid timing noise at high repetition rates. The Bragg reflector is a key component in achieving transform limited pulses with low noise...

  18. Large net-normal dispersion Er-doped fibre laser mode-locked with a nonlinear amplifying loop mirror

    Science.gov (United States)

    Bowen, Patrick; Erkintalo, Miro; Broderick, Neil G. R.

    2018-03-01

    We report on an environmentally stable, all-PM-fibre, Er-doped, mode-locked laser with a central wavelength of 1550 nm. Significantly, the laser possesses large net-normal dispersion such that its dynamics are comparable to that of an all-normal dispersion fibre laser at 1 μm with an analogous architecture. The laser is mode-locked with a nonlinear amplifying loop mirror to produce pulses that are externally compressible to 500 fs. Experimental results are in good agreement with numerical simulations.

  19. Monolithic Hybrid and Passive Mode-Locked 40GHz Quantum Dot Laser Diodes

    DEFF Research Database (Denmark)

    Thompson, M. G.; Larsson, David; Rae, A. R.

    2006-01-01

    For the first time hybrid and passive mode-locking jitter performance is investigated in 40GHz quantum-dot mode-locked lasers. Record low passive mode-locking jitter of 219fs is presented, along with promising hybrid mode-locking results of 124fs....

  20. Electronic control of different generation regimes in mode-locked all-fibre F8 laser

    Science.gov (United States)

    Kobtsev, Sergey; Ivanenko, Aleksey; Kokhanovskiy, Alexey; Smirnov, Sergey

    2018-04-01

    We demonstrate for the first time an electronically controlled realisation of markedly different generation regimes in a mode-locked all-fibre figure-eight (F8) Yb-doped laser. Electronic adjustment of the ratio of pumping powers of two amplification stages in a nonlinear amplifying loop mirror enables the establishment of stable pulse generation regimes with different degrees of coherence and control over their parameters within relatively broad limits, with the pulse duration range exceeding a factor of two in the picosecond domain for coherent and incoherent pulses, the energy range exceeding an order of magnitude for incoherent pulses (2.2-24.8 nJ) and over a factor of 8 for coherent pulses (1.9-16.2 nJ). Adjustment of the pumping powers allows one to maintain the duration of the coherent pulses and to set their peak power in the range of 32.5-292.5 W. The proposed configuration of electronic control over the radiation parameters of a mode-locked all-fibre F8 laser enables reproducible generation of pulses of different types with specified parameters within a broad range of values.

  1. Self-organization of the Q-switched mode-locked regime in a diode-pumped Nd:YAG laser

    Science.gov (United States)

    Donin, V. I.; Yakovin, D. V.; Gribanov, A. V.

    2015-06-01

    A new Q-switched mode-locked generation regime of a solid-state laser, in which a Q-switch is "spontaneously" formed at the frequency of relaxation oscillations, has been observed for the first time. The new generation has been implemented by means of the previously proposed method of an acoustic modulator of a traveling wave in combination with a spherical mirror of a cavity. Stable pulse trains with a repetition frequency of ~30 kHz and a duration of ~2 µs have been observed in the diode-pump Nd:YAG laser with an average output power of ~3 W. Each train contains about 200 equispaced single pulses with a duration of ~45 ps.

  2. Tm-doped fiber laser mode-locking with MoS2-polyvinyl alcohol saturable absorber

    Science.gov (United States)

    Cao, Liming; Li, Xing; Zhang, Rui; Wu, Duanduan; Dai, Shixun; Peng, Jian; Weng, Jian; Nie, Qiuhua

    2018-03-01

    We have designed an all-fiber passive mode-locking thulium-doped fiber laser that uses molybdenum disulfide (MoS2) as a saturable absorber (SA) material. A free-standing few-layer MoS2-polyvinyl alcohol (PVA) film is fabricated by liquid phase exfoliation (LPE) and is then transferred onto the end face of a fiber connector. The excellent saturable absorption of the fabricated MoS2-based SA allows the laser to output soliton pulses at a pump power of 500 mW. Fundamental frequency mode-locking is realized at a repetition frequency of 13.9 MHz. The central wavelength is 1926 nm, the 3 dB spectral bandwidth is 2.86 nm and the pulse duration is 1.51 ps. Additionally, third-order harmonic mode-locking of the laser is also achieved. The pulse duration is 1.33 ps, which is slightly narrower than the fundamental frequency mode-locking bandwidth. The experimental results demonstrate that the few-layer MoS2-PVA SA is promising for use in 2 μm laser systems.

  3. Diverse mode of operation of an all-normal-dispersion mode-locked fiber laser employing two nonlinear loop mirrors.

    Science.gov (United States)

    Chowdhury, Sourav Das; Pal, Atasi; Chatterjee, Sayan; Sen, Ranjan; Pal, Mrinmay

    2018-02-10

    In this paper, we propose an all-normal-dispersion ytterbium-fiber laser with a novel ring cavity architecture having two nonlinear amplifying loop mirrors (NALM) as saturable absorbers, capable of delivering distinctly different pulses with adjustable features. By optimizing the loop lengths of the individual NALMs, the cavity can be operated to deliver Q-switched mode-locked (Q-ML) pulse bunches with adjustable repetition rates, mode-locked pulses in dissipative soliton resonance (DSR) regime or noise-like pulse (NLP) regime with tunable pulse width. The DSR pulses exhibit characteristic narrowband spectrum, while the NLPs exhibit large broadband spectrum. The operation regime of the laser can be controlled by adjusting the amplifier pump powers and the polarization controllers. To the best of the authors' knowledge, this is the first demonstration of a single mode-locked cavity where narrowband DSR pulses and broadband NLPs alongside Q-ML pulse bunches can be selectively generated by employing two NALMs.

  4. Dynamic parabolic pulse generation using temporal shaping of wavelength to time mapped pulses.

    Science.gov (United States)

    Nguyen, Dat; Piracha, Mohammad Umar; Mandridis, Dimitrios; Delfyett, Peter J

    2011-06-20

    Self-phase modulation in fiber amplifiers can significantly degrade the quality of compressed pulses in chirped pulse amplification systems. Parabolic pulses with linear frequency chirp are suitable for suppressing nonlinearities, and to achieve high peak power pulses after compression. In this paper, we present an active time domain technique to generate parabolic pulses for chirped pulse amplification applications. Pulses from a mode-locked laser are temporally stretched and launched into an amplitude modulator, where the drive voltage is designed using the spectral shape of the input pulse and the transfer function of the modulator, resulting in the generation of parabolic pulses. Experimental results of pulse shaping with a pulse train from a mode-locked laser are presented, with a residual error of less than 5%. Moreover, an extinction ratio of 27 dB is achieved, which is ideal for chirped pulse amplification applications.

  5. All-fiber Yb-doped fiber laser passively mode-locking by monolayer MoS2 saturable absorber

    Science.gov (United States)

    Zhang, Yue; Zhu, Jianqi; Li, Pingxue; Wang, Xiaoxiao; Yu, Hua; Xiao, Kun; Li, Chunyong; Zhang, Guangyu

    2018-04-01

    We report on an all-fiber passively mode-locked ytterbium-doped (Yb-doped) fiber laser with monolayer molybdenum disulfide (ML-MoS2) saturable absorber (SA) by three-temperature zone chemical vapor deposition (CVD) method. The modulation depth, saturation fluence, and non-saturable loss of this ML-MoS2 are measured to be 3.6%, 204.8 μJ/cm2 and 6.3%, respectively. Based on this ML-MoS2SA, a passively mode-locked Yb-doped fiber laser has been achieved at 979 nm with pulse duration of 13 ps and repetition rate of 16.51 MHz. A mode-locked fiber laser at 1037 nm is also realized with a pulse duration of 475 ps and repetition rate of 26.5 MHz. To the best of our knowledge, this is the first report that the ML-MoS2 SA is used in an all-fiber Yb-doped mode-locked fiber laser at 980 nm. Our work further points the excellent saturable absorption ability of ML-MoS2 in ultrafast photonic applications.

  6. Measuring a Fiber-Optic Delay Line Using a Mode-Locked Laser

    Science.gov (United States)

    Tu, Meirong; McKee, Michael R.; Pak, Kyung S.; Yu, Nan

    2010-01-01

    The figure schematically depicts a laboratory setup for determining the optical length of a fiber-optic delay line at a precision greater than that obtainable by use of optical time-domain reflectometry or of mechanical measurement of length during the delay-line-winding process. In this setup, the delay line becomes part of the resonant optical cavity that governs the frequency of oscillation of a mode-locked laser. The length can then be determined from frequency-domain measurements, as described below. The laboratory setup is basically an all-fiber ring laser in which the delay line constitutes part of the ring. Another part of the ring - the laser gain medium - is an erbium-doped fiber amplifier pumped by a diode laser at a wavelength of 980 nm. The loop also includes an optical isolator, two polarization controllers, and a polarizing beam splitter. The optical isolator enforces unidirectional lasing. The polarization beam splitter allows light in only one polarization mode to pass through the ring; light in the orthogonal polarization mode is rejected from the ring and utilized as a diagnostic output, which is fed to an optical spectrum analyzer and a photodetector. The photodetector output is fed to a radio-frequency spectrum analyzer and an oscilloscope. The fiber ring laser can generate continuous-wave radiation in non-mode-locked operation or ultrashort optical pulses in mode-locked operation. The mode-locked operation exhibited by this ring is said to be passive in the sense that no electro-optical modulator or other active optical component is used to achieve it. Passive mode locking is achieved by exploiting optical nonlinearity of passive components in such a manner as to obtain ultra-short optical pulses. In this setup, the particular nonlinear optical property exploited to achieve passive mode locking is nonlinear polarization rotation. This or any ring laser can support oscillation in multiple modes as long as sufficient gain is present to overcome

  7. Wide-band residual phase-noise measurements on 40-GHz monolithic mode-locked lasers

    DEFF Research Database (Denmark)

    Larsson, David; Hvam, Jørn Märcher

    2005-01-01

    We have performed wide-band residual phase-noise measurements on semiconductor 40-GHz mode-locked lasers by employing electrical waveguide components for the radio-frequency circuit. The intrinsic timing jitters of lasers with one, two, and three quantum wells (QW) are compared and our design...... prediction, concerning noise versus number of QWs, for the first time corroborated by experiments. A minimum jitter of 44 fs is found, by extrapolating to the Nyquist frequency, for the one-QW device having nearly transform-limited pulses of 1.2 ps. This jitter is nearly three times lower than for a three...

  8. Diode array pumped, non-linear mirror Q-switched and mode-locked ...

    Indian Academy of Sciences (India)

    Abstract. A non-linear mirror consisting of a lithium triborate crystal and a dichroic output coupler are used to mode-lock (passively) an Nd : YVO4 laser, pumped by a diode laser array. The laser can operate both in cw mode-locked and simultaneously Q-switched and mode-locked (QML) regime. The peak power of the laser ...

  9. Diode array pumped, non-linear mirror Q-switched and mode-locked ...

    Indian Academy of Sciences (India)

    A non-linear mirror consisting of a lithium triborate crystal and a dichroic output coupler are used to mode-lock (passively) an Nd : YVO4 laser, pumped by a diode laser array. The laser can operate both in cw mode-locked and simultaneously Q-switched and mode-locked (QML) regime. The peak power of the laser while ...

  10. Diode array pumped, non-linear mirror Q-switched and mode-locked

    Indian Academy of Sciences (India)

    A non-linear mirror consisting of a lithium triborate crystal and a dichroic output coupler are used to mode-lock (passively) an Nd : YVO4 laser, pumped by a diode laser array. The laser can operate both in cw mode-locked and simultaneously Q-switched and mode-locked (QML) regime. The peak power of the laser while ...

  11. Tunable and switchable dual-wavelength passively mode-locked Bi-doped all-fiber ring laser based on nonlinear polarization rotation

    International Nuclear Information System (INIS)

    Luo, A-P; Luo, Z-C; Xu, W-C; Dvoyrin, V V; Mashinsky, V M; Dianov, E M

    2011-01-01

    We demonstrate a tunable and switchable dual-wavelength passively mode-locked Bi-doped all-fiber ring laser by using nonlinear polarization rotation (NPR) technique. Exploiting the spectral filtering effect caused by the combination of the polarizer and intracavity birefringence, the wavelength separation of dual-wavelength mode-locked pulses can be flexibly tuned between 2.38 and 20.45 nm. Taking the advantage of NPR-induced intensity-dependent loss to suppress the mode competition, the stable dual-wavelength pulses output is obtained at room temperature. Moreover, the dual-wavelength switchable operation is achieved by simply rotating the polarization controllers (PCs)

  12. Intracavity KTP-based OPO pumped by a dual-loss modulated, simultaneously Q-switched and mode-locked Nd:GGG laser.

    Science.gov (United States)

    Chu, Hongwei; Zhao, Shengzhi; Yang, Kejian; Zhao, Jia; Li, Yufei; Li, Dechun; Li, Guiqiu; Li, Tao; Qiao, Wenchao

    2014-11-03

    An intracavity KTiOPO(4) (KTP) optical parametric oscillator (OPO) pumped by a simultaneously Q-switched and mode-locked (QML) Nd:Gd(3)Ga(5)O(12) (Nd:GGG) laser with an acousto-optic modulator (AOM) and a Cr(4+):YAG saturable absorber is presented. A minimum mode-locking pulse duration underneath the Q-switched envelope was evaluated to be about 290 ps. A maximum QML output power of 82 mW at the signal wavelength of 1570 nm was achieved, corresponding to a maximum mode-locked pulse energy of about 5.12 μJ. The M(2) values were measured to be about 1.3 and 1.5 for tangential and sagittal directions using knife-edge technique.

  13. Passive harmonic mode-locking of Er-doped fiber laser using CVD-grown few-layer MoS2 as a saturable absorber

    International Nuclear Information System (INIS)

    Xia Han-Ding; Li He-Ping; Lan Chang-Yong; Li Chun; Deng Guang-Lei; Li Jian-Feng; Liu Yong

    2015-01-01

    Passive harmonic mode locking of an erbium-doped fiber laser based on few-layer molybdenum disulfide (MoS 2 ) saturable absorber (SA) is demonstrated. The few-layer MoS 2 is prepared by the chemical vapor deposition (CVD) method and then transferred onto the end face of a fiber connector to form a fiber-compatible MoS 2 SA. The 20th harmonic mode-locked pulses at 216-MHz repetition rate are stably generated with a pulse duration of 1.42 ps and side-mode suppression ratio (SMSR) of 36.1 dB. The results confirm that few-layer MoS 2 can serve as an effective SA for mode-locked fiber lasers. (paper)

  14. All-fiber passively mode-locked thulium-doped fiber ring oscillator operated at solitary and noiselike modes.

    Science.gov (United States)

    Wang, Q; Chen, T; Zhang, B; Heberle, A P; Chen, K P

    2011-10-01

    This Letter presents an all-fiber mode-locked thulium-doped fiber ring oscillator based on nonlinear polarization evolution (NPE). Pumped by an erbium-doped fiber amplified spontaneous emission source, the construction of the laser cavity consisting of only fiber optic components can operate under two different regimes of solitary and noiselike (NL) pulses. Autocorrelation measurements are performed to extract features of these two regimes. © 2011 Optical Society of America

  15. Cavity-augmented frequency tripling of a continuous wave mode-locked laser

    International Nuclear Information System (INIS)

    McConnell, Gail; Ferguson, Allister I.; Langford, Nigel

    2001-01-01

    We present a model and experimental investigation of a singly-resonant optical cavity to enhance the nonlinear conversion efficiency of a continuous wave mode-locked all-solid-state laser source to produce an efficient source of ultraviolet radiation. For input pulses of approximately 33 ps duration at 4.4 ns intervals, our model predicts greater than 30% conversion from fundamental to third harmonic which is particularly attractive for fundamental sources of modest average power. Experimentally, we have achieved overall optical conversion efficiencies from fundamental to third harmonic wavelength typically greater than 11%, compared with less than 0.4% in a single pass geometry. We have measured an average power of 320 mW at λ=355 nm at picosecond pulse duration, which corresponds to a generated third harmonic average power of 0.5 W. (author)

  16. Compact 84 GHz passive mode-locked fiber laser using dual-fiber coupled fused-quartz microresonator

    Science.gov (United States)

    Liu, Tze-An; Hsu, Yung; Chow, Chi-Wai; Chuang, Yi-Chen; Ting, Wei-Jo; Wang, Bo-Chun; Peng, Jin-Long; Chen, Guan-Hong; Chang, Yuan-Chia

    2017-10-01

    We propose and demonstrate a compact and portable-size 84-GHz passive mode-locked fiber laser, in which a dual-fiber coupled fused-quartz microresonator is employed as the intracavity optical comb filter as well as the optical nonlinear material for optical frequency comb generation. About eight coherent optical tones can be generated in the proposed fiber laser. The 20-dB bandwidth is larger than 588 GHz. The full-width half-maximum pulse-width of the proposed laser is 2.5 ps. We also demonstrate the feasibility of using the proposed passive mode-locked fiber laser to carry a 5-Gbit/s on-off-keying signal and transmit over 20-km standard single mode fiber. A 7% forward error correction requirement can be achieved, showing the proposed fiber laser can be a potential candidate for fiber-wireless applications.

  17. Single-shot photonic time-stretch digitizer using a dissipative soliton-based passively mode-locked fiber laser.

    Science.gov (United States)

    Peng, Di; Zhang, Zhiyao; Zeng, Zhen; Zhang, Lingjie; Lyu, Yanjia; Liu, Yong; Xie, Kang

    2018-03-19

    We demonstrate a single-shot photonic time-stretch digitizer using a dissipative soliton-based passively mode-locked fiber laser. The theoretical analysis and simulation results indicate that the dissipative soliton-based optical source with a flat spectrum relieves the envelope-induced signal distortion, and its high energy spectral density helps to improve the signal-to-noise ratio, both of which are favorable for simplifying the optical front-end architecture of a photonic time-stretch digitizer. By employing a homemade dissipative soliton-based passively mode-locked erbium-doped fiber laser in a single-shot photonic time-stretch digitizer, an effective number of bits of 4.11 bits under an effective sampling rate of 100 GS/s is experimentally obtained without optical amplification in the link and pulse envelope removing process.

  18. Soliton compression of the erbium-doped fiber laser weakly started mode-locking by nanoscale p-type Bi2Te3 topological insulator particles

    Science.gov (United States)

    Lin, Yung-Hsiang; Yang, Chun-Yu; Lin, Sheng-Feng; Tseng, Wei-Hsuan; Bao, Qiaoliang; Wu, Chih-I.; Lin, Gong-Ru

    2014-05-01

    We demonstrate the nanoscale p-type Bi2Te3 powder-based saturable absorber-induced passive mode-locking of the erbium-doped fiber laser (EDFL) with sub-picosecond pulsewidth. Such a nanoscale topological insulator powder is obtained by polishing the bulk p-type Bi2Te3 in a commercial thermoelectric cooler (TE cooler). This is then directly brushed onto the end-face of a single-mode fiber patchcord, to avoid any mis-connecting loss caused by laser beam divergence, which can result in a mode-locked pulsewidth of 436 fs in the self-amplitude modulation mode of a TE cooler. To further shorten the pulse, the soliton compression is operated by well-controlling the group delay dispersion and self-phase modulation, providing the passively mode-locked EDFL with a pulsewidth as short as 403 fs.

  19. Widely power-tunable polarization-independent ultrafast mode-locked fiber laser using bulk InN as saturable absorber.

    Science.gov (United States)

    Jimenez-Rodriguez, M; Monteagudo-Lerma, L; Monroy, E; González-Herráez, M; Naranjo, F B

    2017-03-06

    The growing demand of ultrafast mode-locked fiber lasers in the near infrared has boosted the research activity in this area. One of the most convenient ways to achieve passive mode locking consists of inserting a semiconductor saturable absorber in the laser cavity to modulate the losses. However, in such a configuration, the limited power range of operation is still an unsolved issue. Here we report the fabrication of an ultrafast, high-power, widely power-tunable and non-polarization-dependent mode-locked fiber laser operating at 1.55 µm, using an InN layer as saturable absorber. With post-amplification, this laser delivers 55-fs pulses with a repetition rate of 4.84 MHz and peak power in the range of 1 MW in an all-fiber arrangement.

  20. Simulation of dissipative-soliton-resonance generation in a passively mode-locked Yb-doped fiber laser

    Science.gov (United States)

    Du, Wenxiong; Li, Heping; Liu, Cong; Shen, Shengnan; Zhang, Shangjian; Liu, Yong

    2017-10-01

    We present a numerical investigation of dissipative-soliton-resonance (DSR) generation in an all-normal-dispersion Ybdoped fiber laser mode-locked by a real saturable absorber (SA). In the simulation model, the SA includes both the saturable absorption and excited-state absorption (ESA) effects. The intra-cavity pulse evolution is numerically simulated with different transmission functions of SA. When omitting the ESA effect, the transmissivity of SA increases monotonically with the input pulse power. The noise-like pulse (NLP) operation in the cavity is obtained at high pump power, which is attributed to the spectral filtering effect. When the ESA effect is activated, higher instantaneous power part of pulse encounters larger loss induced by SA, causing that the pulse peak power is clamped at a certain fixed value. With increasing pump, the pulse starts to extend in the time domain while the pulse spectrum is considerably narrowed. In this case, the NLP operation state induced by the spectral filtering effect is avoided and the DSR is generated. Our simulation results indicate that the ESA effect in the SA plays a dominant role in generating the DSR pulses, which will be conducive to comprehending the mechanism of DSR generation in passively mode-locked fiber lasers.

  1. Class-A mode-locked lasers: Fundamental solutions

    Science.gov (United States)

    Kovalev, Anton V.; Viktorov, Evgeny A.

    2017-11-01

    We consider a delay differential equation (DDE) model for mode-locked operation in class-A semiconductor lasers containing both gain and absorber sections. The material processes are adiabatically eliminated as these are considered fast in comparison to the delay time for a long cavity device. We determine the steady states and analyze their bifurcations using DDE-BIFTOOL [Engelborghs et al., ACM Trans. Math. Software 28, 1 (2002)]. Multiple forms of coexistence, transformation, and hysteretic behavior of stable steady states and fundamental periodic regimes are discussed in bifurcation diagrams.

  2. Effect of thermal management on the properties of saturable absorber mirrors in high-power mode-locked semiconductor disk lasers

    International Nuclear Information System (INIS)

    Rantamäki, Antti; Lyytikäinen, Jari; Jari Nikkinen; Okhotnikov, Oleg G

    2011-01-01

    The thermal management of saturable absorbers is shown to have a critical impact on a high-power mode-locked disk laser. The absorber with efficient heat removal makes it possible to generate ultrashort pulses with high repetition rates and high power density.

  3. Optical parametric generation by a simultaneously Q-switched mode-locked single-oscillator thulium-doped fiber laser in orientation-patterned gallium arsenide.

    Science.gov (United States)

    Donelan, Brenda; Kneis, Christian; Scurria, Giuseppe; Cadier, Benoît; Robin, Thierry; Lallier, Eric; Grisard, Arnaud; Gérard, Bruno; Eichhorn, Marc; Kieleck, Christelle

    2016-11-01

    Optical parametric generation is demonstrated in orientation-patterned gallium arsenide, pumped by a novel single-oscillator simultaneously Q-switched and mode-locked thulium-doped fiber laser, downconverting the pump radiation into the mid-infrared wavelength regime. The maximum output energy reached is greater than 2.0 μJ per pump pulse.

  4. Comparison of symmetric and asymmetric double quantum well extended-cavity diode lasers for broadband passive mode-locking at 780  nm.

    Science.gov (United States)

    Christopher, Heike; Kovalchuk, Evgeny V; Wenzel, Hans; Bugge, Frank; Weyers, Markus; Wicht, Andreas; Peters, Achim; Tränkle, Günther

    2017-07-01

    We present a compact, mode-locked diode laser system designed to emit a frequency comb in the wavelength range around 780 nm. We compare the mode-locking performance of symmetric and asymmetric double quantum well ridge-waveguide diode laser chips in an extended-cavity diode laser configuration. By reverse biasing a short section of the diode laser chip, passive mode-locking at 3.4 GHz is achieved. Employing an asymmetric double quantum well allows for generation of a mode-locked optical spectrum spanning more than 15 nm (full width at -20  dB) while the symmetric double quantum well device only provides a bandwidth of ∼2.7  nm (full width at -20  dB). Analysis of the RF noise characteristics of the pulse repetition rate shows an RF linewidth of about 7 kHz (full width at half-maximum) and of at most 530 Hz (full width at half-maximum) for the asymmetric and symmetric double quantum well devices, respectively. Investigation of the frequency noise power spectral density at the pulse repetition rate shows a white noise floor of approximately 2100  Hz 2 /Hz and of at most 170  Hz 2 /Hz for the diode laser employing the asymmetric and symmetric double quantum well structures, respectively. The pulse width is less than 10 ps for both devices.

  5. Kerr-lens mode-locked Ti:Sapphire laser pumped by a single laser diode

    Science.gov (United States)

    Kopylov, D. A.; Esaulkov, M. N.; Kuritsyn, I. I.; Mavritskiy, A. O.; Perminov, B. E.; Konyashchenko, A. V.; Murzina, T. V.; Maydykovskiy, A. I.

    2018-04-01

    The performance of a Ti:sapphire laser pumped by a single 461 nm laser diode is presented for both the continuous-wave and the mode-locked regimes of operation. We introduce a simple astigmatism correction scheme for the laser diode beam consisting of two cylindrical lenses affecting the pump beam along the fast axis of the laser diode, which provides the mode-matching between the nearly square-shaped pump beam and the cavity mode. The resulting efficiency of the suggested Ti:Sapphire oscillator pumped by such a laser diode is analyzed for the Ti:sapphire crystals of 3 mm, 5 mm and 10 mm in length. We demonstrate that such a system provides the generation of ultrashort pulses up to 15 fs in duration with the repetition rate of 87 MHz, the average power being 170 mW.

  6. Characterization of a FBG sensor interrogation system based on a mode-locked laser scheme.

    Science.gov (United States)

    Madrigal, Javier; Fraile-Peláez, Francisco Javier; Zheng, Di; Barrera, David; Sales, Salvador

    2017-10-02

    This paper is focused on the characterization of a fiber Bragg grating (FBG) sensor interrogation system based on a fiber ring laser with a semiconductor optical amplifier as the gain medium, and an in-loop electro-optical modulator. This system operates as a switchable active (pulsed) mode-locked laser. The operation principle of the system is explained theoretically and validated experimentally. The ability of the system to interrogate an array of different FBGs in wavelength and spatial domain is demonstrated. Simultaneously, the influence of several important parameters on the performance of the interrogation technique has been investigated. Specifically, the effects of the bandwidth and the reflectivity of the FBGs, the SOA gain, and the depth of the intensity modulation have been addressed.

  7. Bright-dark rogue wave in mode-locked fibre laser (Conference Presentation)

    Science.gov (United States)

    Kbashi, Hani; Kolpakov, Stanislav; Martinez, Amós; Mou, Chengbo; Sergeyev, Sergey V.

    2017-05-01

    Bright-Dark Rogue Wave in Mode-Locked Fibre Laser Hani Kbashi1*, Amos Martinez1, S. A. Kolpakov1, Chengbo Mou, Alex Rozhin1, Sergey V. Sergeyev1 1Aston Institute of Photonic Technologies, School of Engineering and Applied Science Aston University, Birmingham, B4 7ET, UK kbashihj@aston.ac.uk , 0044 755 3534 388 Keywords: Optical rogue wave, Bright-Dark rogue wave, rogue wave, mode-locked fiber laser, polarization instability. Abstract: Rogue waves (RWs) are statistically rare localized waves with high amplitude that suddenly appear and disappear in oceans, water tanks, and optical systems [1]. The investigation of these events in optics, optical rogue waves, is of interest for both fundamental research and applied science. Recently, we have shown that the adjustment of the in-cavity birefringence and pump polarization leads to emerge optical RW events [2-4]. Here, we report the first experimental observation of vector bright-dark RWs in an erbium-doped stretched pulse mode-locked fiber laser. The change of induced in-cavity birefringence provides an opportunity to observe RW events at pump power is a little higher than the lasing threshold. Polarization instabilities in the laser cavity result in the coupling between two orthogonal linearly polarized components leading to the emergence of bright-dark RWs. The observed clusters belongs to the class of slow optical RWs because their lifetime is of order of a thousand of laser cavity roundtrip periods. References: 1. D. R. Solli, C. Ropers, P. Koonath,and B. Jalali, Optical rogue waves," Nature, 450, 1054-1057, 2007. 2. S. V. Sergeyev, S. A. Kolpakov, C. Mou, G. Jacobsen, S. Popov, and V. Kalashnikov, "Slow deterministic vector rogue waves," Proc. SPIE 9732, 97320K (2016). 3. S. A. Kolpakov, H. Kbashi, and S. V. Sergeyev, "Dynamics of vector rogue waves in a fiber laser with a ring cavity," Optica, 3, 8, 870, (2016). 5. S. Kolpakov, H. Kbashi, and S. Sergeyev, "Slow optical rogue waves in a unidirectional fiber laser

  8. Fundamental and harmonic soliton mode-locked erbium-doped fiber laser using single-walled carbon nanotubes embedded in poly (ethylene oxide) film saturable absorber

    Science.gov (United States)

    Rosdin, R. Z. R. R.; Zarei, A.; Ali, N. M.; Arof, H.; Ahmad, H.; Harun, S. W.

    2015-01-01

    This paper presents a simple, compact and low cost mode-locked Erbium-doped fiber laser (EDFL) using a single-walled carbon nanotubes (SWCNTs) embedded in poly(ethylene oxide) (PEO) film as a passive saturable absorber. The film was fabricated using a prepared homogeneous SWCNT solution, which was mixed with a diluted PEO solution and casted onto a glass petri dish to form a thin film by evaporation technique. The film, with a thickness of 50 μm, is sandwiched between two fiber connectors to construct a saturable absorber, which is then integrated in an EDFL cavity to generate a self-started stable soliton pulses operating at 1560.8 nm. The soliton pulse starts to lase at 1480 nm pup power threshold of 12.3 mW to produce pulse train with repetition rate of 11.21 MHz, pulse width of 1.02 ps, average output power of 0.65 mW and pulse energy of 57.98 pJ. Then, we observed the 4th, 7th and 15th harmonic of fundamental cavity frequency start to occur when the pump powers are further increased to 14.9, 17.5 and 20.1 mW, respectively. The 4th harmonic pulses are characterized in detail with a repetition rate of 44.84 MHz, a transform-limited pulse width of 1.19 ps, side-mode suppression ratio of larger than 20 dB and pulse energy of 9.14 pJ.

  9. Fourier Domain Mode Locking (FDML): A new laser operating regime and applications for optical coherence tomography.

    Science.gov (United States)

    Huber, R; Wojtkowski, M; Fujimoto, J G

    2006-04-17

    We demonstrate a new technique for frequency-swept laser operation--Fourier domain mode locking (FDML)--and its application for swept-source optical coherence tomography (OCT) imaging. FDML is analogous to active laser mode locking for short pulse generation, except that the spectrum rather than the amplitude of the light field is modulated. High-speed, narrowband optical frequency sweeps are generated with a repetition period equal to the fundamental or a harmonic of cavity round-trip time. An FDML laser is constructed using a long fiber ring cavity, a semiconductor optical amplifier, and a tunable fiber Fabry-Perot filter. Effective sweep rates of up to 290 kHz are demonstrated with a 105 nm tuning range at 1300 nm center wavelength. The average output power is 3mW directly from the laser and 20 mW after post-amplification. Using the FDML laser for swept-source OCT, sensitivities of 108 dB are achieved and dynamic linewidths are narrow enough to enable imaging over a 7 mm depth with only a 7.5 dB decrease in sensitivity. We demonstrate swept-source OCT imaging with acquisition rates of up to 232,000 axial scans per second. This corresponds to 906 frames/second with 256 transverse pixel images, and 3.5 volumes/second with a 256x128x256 voxel element 3-DOCT data set. The FDML laser is ideal for swept-source OCT imaging, thus enabling high imaging speeds and large imaging depths.

  10. Independent tunability of the double-mode-locked cw dye laser.

    LENUS (Irish Health Repository)

    Bourkoff, E

    1979-06-01

    We report a new configuration that enables the double-mode-locked cw dye laser to be independently tunable. In addition, the output coupling at each of the two wavelengths can be independently specified. A series of oscillographs shows some interesting features unique to double mode locking and also shows the effects of varying the two cavity lengths with respect to each other.

  11. Comparison of the noise performance of 10GHz QW and QD mode-locked laser diodes

    DEFF Research Database (Denmark)

    Carpintero, Guillermo; Thompson, Mark G.; Yvind, Kresten

    2010-01-01

    This paper reports the experimental characterization of the noise performance of a quantum dot and a quantum well 10GHz passive mode locked laser diodes.......This paper reports the experimental characterization of the noise performance of a quantum dot and a quantum well 10GHz passive mode locked laser diodes....

  12. Modeling of mode-locked coupled-resonator optical waveguide lasers

    DEFF Research Database (Denmark)

    Agger, Christian; Skovgård, Troels Suhr; Gregersen, Niels

    2010-01-01

    Coupled-resonator optical waveguides made from coupled high-Q photonic crystal nanocavities are investigated for use as cavities in mode-locked lasers. Such devices show great potential in slowing down light and can serve to reduce the cavity length of a mode-locked laser. An explicit expression...

  13. A SESAM passively mode-locked fiber laser with a long cavity including a band pass filter

    International Nuclear Information System (INIS)

    Song, Rui; Chen, Hong-Wei; Chen, Sheng-Ping; Hou, Jing; Lu, Qi-Sheng

    2011-01-01

    A semiconductor saturable absorber mirror (SESAM) passively mode-locked fiber laser with a long cavity length over 700 m is demonstrated. A band pass filter is inserted into the laser cavity to stabilize the lasing wavelength. Some interesting phenomena are observed and discussed. The central wavelength, repetition rate, average power and single pulse energy of the laser are 1064 nm, 281.5 kHz, 11 mW and 39 nJ, respectively. The laser operates stably without Q-switching instabilities, which greatly reduces the damage opportunities of the SESAM

  14. Robust, low-noise, polarization-maintaining mode-locked Er-fiber laser with a planar lightwave circuit (PLC) device as a multi-functional element.

    Science.gov (United States)

    Kim, Chur; Kwon, Dohyeon; Kim, Dohyun; Choi, Sun Young; Cha, Sang Jun; Choi, Ki Sun; Yeom, Dong-Il; Rotermund, Fabian; Kim, Jungwon

    2017-04-15

    We demonstrate a new planar lightwave circuit (PLC)-based device, integrated with a 980/1550 wavelength division multiplexer, an evanescent-field-interaction-based saturable absorber, and an output tap coupler, which can be employed as a multi-functional element in mode-locked fiber lasers. Using this multi-functional PLC device, we demonstrate a simple, robust, low-noise, and polarization-maintaining mode-locked Er-fiber laser. The measured full-width at half-maximum bandwidth is 6 nm centered at 1555 nm, corresponding to 217 fs transform-limited pulse duration. The measured RIN and timing jitter are 0.22% [10 Hz-10 MHz] and 6.6 fs [10 kHz-1 MHz], respectively. Our results show that the non-gain section of mode-locked fiber lasers can be easily implemented as a single PLC chip that can be manufactured by a wafer-scale fabrication process. The use of PLC processes in mode-locked lasers has the potential for higher manufacturability of low-cost and robust fiber and waveguide lasers.

  15. Femtosecond mode-locked erbium-doped fiber laser based on MoS2-PVA saturable absorber

    Science.gov (United States)

    Ahmed, M. H. M.; Latiff, A. A.; Arof, H.; Ahmad, H.; Harun, S. W.

    2016-08-01

    We fabricate a free-standing few-layer molybdenum disulfide (MoS2)-polymer composite by liquid phase exfoliation of chemically pristine MoS2 crystals and use this to demonstrate a soliton mode-locked Erbium-doped fiber laser (EDFL). A stable self-started mode-locked soliton pulse is generated by fine-tuning the rotation of the polarization controller at a low threshold pump power of 25 mW. Its solitonic behavior is verified by the presence of Kelly sidebands in the output spectrum. The central wavelength, pulse width, and repetition rate of the laser are 1573.7 nm, 630 fs, and 27.1 MHz, respectively. The maximum pulse energy is 0.141 nJ with peak power of 210 W at pump power of 170 mW. This result contributes to the growing body of work studying the nonlinear optical properties of transition metal dichalcogenides that present new opportunities for ultrafast photonic applications.

  16. Nanoscale charcoal powder induced saturable absorption and mode-locking of a low-gain erbium-doped fiber-ring laser

    Science.gov (United States)

    Lin, Yung-Hsiang; Chi, Yu-Chieh; Lin, Gong-Ru

    2013-05-01

    Triturated charcoal nano-powder directly brushed on a fiber connector end-face is used for the first time as a fast saturable absorber for a passively mode-locked erbium-doped fiber-ring laser (EDFL). These dispersant-free charcoal nano-powders with a small amount of crystalline graphene phase and highly disordered carbon structure exhibit a broadened x-ray diffraction peak and their Raman spectrum shows the existence of a carbon related D-band at 1350 cm-1 and the disappearance of the 2D-band peak at 2700 cm-1. The charcoal nano-powder exhibits a featureless linear absorbance in the infrared region with its linear transmittance of 0.66 nonlinearly saturated at 0.73 to give a ΔT/T of 10%. Picosecond mode-locking at a transform-limited condition of a low-gain EDFL is obtained by using the charcoal nano-powder. By using a commercial EDFA with a linear gain of only 17 dB at the saturated output power of 17.5 dB m required to initiate the saturable absorption of the charcoal nano-powder, the EDFL provides a pulsewidth narrowing from 3.3 to 1.36 ps associated with its spectral linewidth broadening from 0.8 to 1.83 nm on increasing the feedback ratio from 30 to 90%. This investigation indicates that all the carbon-based materials containing a crystalline graphene phase can be employed to passively mode-lock the EDFL, however, the disordered carbon structure inevitably induces a small modulation depth and a large mode-locking threshold, thus limiting the pulsewidth shortening. Nevertheless, the nanoscale charcoal passively mode-locked EDFL still shows the potential to generate picosecond pulses under a relatively low cavity gain. An appropriate cavity design can be used to compensate this defect-induced pulsewidth limitation and obtain a short pulsewidth.

  17. Hybrid silicon mode-locked laser with improved RF power by impedance matching

    Science.gov (United States)

    Tossoun, Bassem; Derickson, Dennis; Srinivasan, Sudharsanan; Bowers, John

    2015-02-01

    We design and discuss an impedance matching solution for a hybrid silicon mode-locked laser diode (MLLD) to improve peak optical power coming from the device. In order to develop an impedance matching solution, a thorough measurement and analysis of the MLLD as a function of bias on each of the laser segments was carried out. A passive component impedance matching network was designed at the operating frequency of 20 GHz to optimize RF power delivery to the laser. The hybrid silicon laser was packaged together in a module including the impedance matching circuit. The impedance matching design resulted in a 6 dB (electrical) improvement in the detected modulation spectrum power, as well as approximately a 10 dB phase noise improvement, from the MLLD. Also, looking ahead to possible future work, we discuss a Step Recovery Diode (SRD) driven impulse generator, which wave-shapes the RF drive to achieve efficient injection. This novel technique addresses the time varying impedance of the absorber as the optical pulse passes through it, to provide optimum optical pulse shaping.

  18. Mode-locked Tm-doped fiber laser based on iron-doped carbon nitride nanosheets

    Science.gov (United States)

    Luo, Yongfeng; Zhou, Yan; Tang, Yulong; Xu, Jianqiu; Hu, Chenxia; Gao, Linfeng; Zhang, Haoli; Wang, Qiang

    2017-11-01

    Solution based nanosheets of iron-doped graphitic carbon nitrides (Fe-g-CN) have been prepared and their optical properties (both linear and nonlinear) are studied. These two-dimensional (2D) nanosheets show an absorption spectrum extending to over 2 µm, and in particular they possess strong nonlinear (saturable) absorption in the 2 µm spectral region. A saturable absorber (SA) manufactured from 2D Fe-g-CN nanosheets gives a modulation depth and saturation intensity of 12.9% and 8.9 MW cm‑2, respectively. This SA is further used to mode-lock thulium-doped fiber lasers, producing 2 µm laser pulses with a duration of 16.6 ps (dechirped to 2.2 ps), an average power of 96.4 mW, a pulse energy of 6.3 nJ, and a repetition rate of 15.3 MHz. As a new type of 2D nonlinear material with strong modulation capabilities, solution-based Fe-g-CN nanosheets can be potentially integrated into photonic and optoelectrionic devices, particuarly in the 2 µm spectral region.

  19. Time-Gating Processes in Intra-Cavity Mode-Locking Devices Like Saturable Absorbers and Kerr Cells

    Science.gov (United States)

    Prasad, Narasimha; Roychoudhuri, Chandrasekhar

    2010-01-01

    Photons are non-interacting entities. Light beams do not interfere by themselves. Light beams constituting different laser modes (frequencies) are not capable of re-arranging their energies from extended time-domain to ultra-short time-domain by themselves without the aid of light-matter interactions with suitable intra-cavity devices. In this paper we will discuss the time-gating properties of intra-cavity "mode-locking" devices that actually help generate a regular train of high energy wave packets.

  20. Passive mode locking and formation of dissipative solitons in electron oscillators with a bleaching absorber in the feedback loop

    Energy Technology Data Exchange (ETDEWEB)

    Ginzburg, N. S., E-mail: ginzburg@appl.sci-nnov.ru; Kocharovskaya, E. R.; Vilkov, M. N.; Sergeev, A. S. [Russian Academy of Sciences, Institute of Applied Physics (Russian Federation)

    2017-01-15

    The mechanisms of passive mode locking and formation of ultrashort pulses in microwave electron oscillators with a bleaching absorber in the feedback loop have been analyzed. It is shown that in the group synchronism regime in which the translational velocity of particles coincides with the group velocity of the electromagnetic wave, the pulse formation can be described by the equations known in the theory of dissipative solitons. At the same time, the regimes in which the translational velocity of electrons differs from the group velocity and the soliton being formed and moving along the electron beam consecutively (cumulatively) receives energy from various electron fractions are optimal for generating pulses with the maximal peak amplitudes.

  1. Construction and Measurement of an Actively Mode-Locked Sigma Laser

    National Research Council Canada - National Science Library

    Butler, James

    1998-01-01

    .... The amplitude-modulated pulses become the discrete samples of the analog signal. Limiting factors in an optical ADC are the pulsewidth, the pulse rate, and the jitter noise of the optical pulse train...

  2. High speed engine gas thermometry by Fourier-domain mode-locked laser absorption spectroscopy.

    Science.gov (United States)

    Kranendonk, Laura A; An, Xinliang; Caswell, Andrew W; Herold, Randy E; Sanders, Scott T; Huber, Robert; Fujimoto, James G; Okura, Yasuhiro; Urata, Yasuhiro

    2007-11-12

    We present a novel method for low noise, high-speed, real-time spectroscopy to monitor molecular absorption spectra. The system is based on a rapidly swept, narrowband CW Fourier-domain mode-locked (FDML) laser source for spectral encoding in time and an optically time-multiplexed split-pulse data acquisition system for improved noise performance and sensitivity. An acquisition speed of ~100 kHz, a spectral resolution better than 0.1 nm over a wavelength range of ~1335-1373 nm and a relative noise level of ~5 mOD (~1% minimum detectable base-e absorbance) are achieved. The system is applied for crank-angle-resolved gas thermometry by H(2)O absorption spectroscopy in an engine motoring at 600 and 900 rpm with a precision of ~1%. Influences of various noise sources such as laser phase and intensity noise, trigger and synchronization jitter in the electronic detection system, and the accuracy of available H(2)O absorption databases are discussed.

  3. Compact mode-locked diode laser system for high precision frequency comparisons in microgravity

    Science.gov (United States)

    Christopher, H.; Kovalchuk, E. V.; Wicht, A.; Erbert, G.; Tränkle, G.; Peters, A.

    2017-11-01

    Nowadays cold atom-based quantum sensors such as atom interferometers start leaving optical labs to put e.g. fundamental physics under test in space. One of such intriguing applications is the test of the Weak Equivalence Principle, the Universality of Free Fall (UFF), using different quantum objects such as rubidium (Rb) and potassium (K) ultra-cold quantum gases. The corresponding atom interferometers are implemented with light pulses from narrow linewidth lasers emitting near 767 nm (K) and 780 nm (Rb). To determine any relative acceleration of the K and Rb quantum ensembles during free fall, the frequency difference between the K and Rb lasers has to be measured very accurately by means of an optical frequency comb. Micro-gravity applications not only require good electro-optical characteristics but are also stringent in their demand for compactness, robustness and efficiency. For frequency comparison experiments the rather complex fiber laser-based frequency comb system may be replaced by one semiconductor laser chip and some passive components. Here we present an important step towards this direction, i.e. we report on the development of a compact mode-locked diode laser system designed to generate a highly stable frequency comb in the wavelength range of 780 nm.

  4. CsPbBr3 nanocrystal saturable absorber for mode-locking ytterbium fiber laser

    Science.gov (United States)

    Zhou, Yan; Hu, Zhiping; Li, Yue; Xu, Jianqiu; Tang, Xiaosheng; Tang, Yulong

    2016-06-01

    Cesium lead halide perovskite nanocrystals (CsPbX3, X = Cl, Br, I) have been reported as efficient light-harvesting and light-emitting semiconductor materials, but their nonlinear optical properties have been seldom touched upon. In this paper, we prepare layered CsPbBr3 nanocrystal films and characterize their physical properties. Broadband linear absorption from ˜0.8 to over 2.2 μm and nonlinear optical absorption at the 1-μm wavelength region are measured. The CsPbBr3 saturable absorber (SA), manufactured by drop-casting of colloidal CsPbBr3 liquid solution on a gold mirror, shows modulation depth and saturation intensity of 13.1% and 10.7 MW/cm2, respectively. With this SA, mode-locking operation of a polarization-maintained ytterbium fiber laser produces single pulses with duration of ˜216 ps, maximum average output power of 10.5 mW, and the laser spectrum is centered at ˜1076 nm. This work shows that CsPbBr3 films can be efficient SA candidates for fiber lasers and also have great potential to become broadband linear and nonlinear optical materials for photonics and optoelectronics.

  5. 80  nJ ultrafast dissipative soliton generation in dumbbell-shaped mode-locked fiber laser.

    Science.gov (United States)

    Chen, He; Chen, Sheng-Ping; Jiang, Zong-Fu; Hou, Jing

    2016-09-15

    A novel all-fiberized dumbbell-shaped mode-locked fiber laser was developed to directly generate 80 nJ dissipative solitons, which can be linearly compressed from 85 to 1.2 ps externally with a diffraction grating pair. The pulse peak power reached 42 kW after compression. With the most available pump power, stable dissipative soliton bundles with up to 628 nJ bundle energy were obtained. The corresponding average output power reached 2.2 W. The employment of dual-nonlinear-optical-loop mirrors and large-mode-area fibers in the cavity played an essential role in improving structural compactness and producing high-energy ultrafast pulses. To the best of our knowledge, these are the most energetic compressible dissipative solitons generated from a strictly all-fiber cavity.

  6. Laser ablation comparison by picosecond pulses train and nanosecond pulse

    Science.gov (United States)

    Lednev, V. N.; Filippov, M. N.; Bunkin, A. F.; Pershin, S. M.

    2015-12-01

    A comparison of laser ablation by a train of picosecond pulses and nanosecond pulses revealed a difference in laser craters, ablation thresholds, plasma sizes and spectral line intensities. Laser ablation with a train of picosecond pulses resulted in improved crater quality while ablated mass decreased up to 30%. A reduction in laser plasma dimensions for picosecond train ablation was observed while the intensity of atomic/ionic lines in the plasma spectra was greater by a factor of 2-4 indicating an improved excitation and atomization in the plasma.

  7. Superluminescent high-efficient parametric generation in PPLN crystal with pumping by a Q-switched mode locked Nd:YAG laser

    Science.gov (United States)

    Donin, V. I.; Yakovin, D. V.; Yakovin, M. D.; Gribanov, A. V.

    2018-03-01

    We present results on parametric superluminescence in a periodically poled lithium niobate crystal pumped by a train of 45 ps pulses using a Q-switched mode locked Nd:YAG laser. The conversion efficiency (with respect to the absorbed power) was ~83%. To the best of our knowledge, this is the highest efficiency obtained with powerful superluminescent parametric sources. At the average pumping power of the laser of ~0.5 W and repetition rates of 1 and 1.7 kHz, the peak total output powers were as high as 210 and 200 kW, and the powers of the idler wavelength (3.82 µm) were 55 and 50 kW. New lines in the visible and UV spectrum were observed and are explained. The experiments demonstrated that the spectral and angular characteristics of superluminescence are determined by the pumping laser. In particular, the line width of the signal wave was close to that of the pumping line at ~200 GHz, and the divergence of the signal and idler waves depended only on the convergence (divergence) angle of the pumping radiation (30 mrad) and was independent of the wavelength.

  8. Academic Training - Pulsed SC Magnets

    CERN Multimedia

    Françoise Benz

    2006-01-01

    2005-2006 ACADEMIC TRAINING PROGRAMME LECTURE SERIES 2, 3, June 29, 30, 31 May, 1, 2 June 11:00-12:00 - Auditorium, bldg 500 Pulsed SC Magnets by M. Wilson Lecture 1. Introduction to Superconducting Materials Type 1,2 and high temperature superconductors; their critical temperature, field & current density. Persistent screening currents and the critical state model. Lecture 2. Magnetization and AC Loss How screening currents cause irreversible magnetization and hysteresis loops. Field errors caused by screening currents. Flux jumping. The general formulation of ac loss in terms of magnetization. AC losses caused by screening currents. Lecture 3. Twisted Wires and Cables Filamentary composite wires and the losses caused by coupling currents between filaments, the need for twisting. Why we need cables and how the coupling currents in cables contribute more ac loss. Field errors caused by coupling currents. Lecture 4. AC Losses in Magnets, Cooling and Measurement Summary of all loss mech...

  9. Influence of gain fiber on dissipative soliton pairs in passively mode-locked fiber laser based on BP as a saturable absorber

    Science.gov (United States)

    Gao, Bo; Ma, Chunyang; Huo, Jiayu; Guo, Yubin; Sun, Tiegang; Wu, Ge

    2018-03-01

    We investigate the influence of gain fiber on dissipative soliton pairs in passively mode-locked (PML) fiber laser based on black phosphorus (BP) as a saturable absorber. Numerical simulations show that we can generate the dissipative soliton pairs in PML fiber laser when the gain fiber parameters (gain saturation energy and gain bandwidth) are in an appropriate dynamic range, and the dissipative soliton pairs become unstable once the range is exceeded. Then we analyze the dynamic evolution of the dissipative soliton pairs and the influence of gain fiber on the pulse separation, peak power, and single-pulse energy of the dissipative solitons pairs.

  10. Mode-locked thin-disk lasers and their potential application for high-power terahertz generation

    Science.gov (United States)

    Saraceno, Clara J.

    2018-04-01

    The progress achieved in the last few decades in the performance of ultrafast laser systems with high average power has been tremendous, and continues to provide momentum to new exciting applications, both in scientific research and technology. Among the various technological advances that have shaped this progress, mode-locked thin-disk oscillators have attracted significant attention as a unique technology capable of providing ultrashort pulses with high energy (tens to hundreds of microjoules) and at very high repetition rates (in the megahertz regime) from a single table-top oscillator. This technology opens the door to compact high repetition rate ultrafast sources spanning the entire electromagnetic spectrum from the XUV to the terahertz regime, opening various new application fields. In this article, we focus on their unexplored potential as compact driving sources for high average power terahertz generation.

  11. Amplitude and Temporal Jitter Associated with the NPS Active Mode-Locked Sigma Laser

    National Research Council Canada - National Science Library

    Anderson, James

    2000-01-01

    .... They have the capability of being used for direct signal reception and ADC at an antenna. A fundamental requirement for these designs is a high-frequency optical pulse train with uniform amplitude and pulse spacing...

  12. Quantum dot cadmium selenide as a saturable absorber for Q-switched and mode-locked double-clad ytterbium-doped fiber lasers

    Science.gov (United States)

    Mahyuddin, M. B. H.; Latiff, A. A.; Rusdi, M. F. M.; Irawati, N.; Harun, S. W.

    2017-08-01

    This paper demonstrates the integration of quantum dot (QD) cadmium selenide (CdSe) nanoparticles, which is embedded into polymethyl methacrylate (PMMA) film into an ytterbium-doped fiber laser (YDFL) cavity to produce Q-switched and mode-locked fiber lasers. The QD CdSe based film functions as a saturable absorber (SA). For Q-switching operation, stable pulse is generated within 970-1200 mW pump power, with tunable repetition rate and pulse width of 24.5-40.5 kHz and 6.8-3.7 μs, respectively. Maximum pulse energy and peak power are obtained about 1.1 μJ and 0.28 W, respectively. As we tune the polarization state of the laser cavity and use a single QD CdSe film, the mode-locking operation could also be generated within 310-468 mW pump power with repetition rate of 14.5 MHz and pulse width of 3.5 ps. Maximum pulse energy and peak power are obtained about 2 nJ and 0.11 W, respectively. These results may contribute to continuous research work on laser pulse generation, providing new opportunities of CdSe material in photonics applications.

  13. Multiwavelength mode-locked cylindrical vector beam fiber laser based on mode selective coupler

    Science.gov (United States)

    Huang, Ping; Cai, Yu; Zhang, Zuxing

    2017-10-01

    We propose and demonstrate a multiwavelength mode-locked fiber laser with cylindrical vector beam generation for the first time, to the best of our knowledge. The mode-locking mechanism is nonlinear polarization rotation, and the multiwavelength operation is contributed to the in-line birefringence fiber filter with periodic multiple passbands formed by incorporating a section of polarization maintaining fiber into the laser cavity with a polarizer. Furthermore, using the mode selective coupler, which acts as mode converter from fundamental mode to higher-order mode, multiwavelength mode-locked cylindrical vector beams have been obtained, which may have potential applications in mode-division multiplexing optical fiber communication and material processing.

  14. Fourier domain mode-locked swept source at 1050 nm based on a tapered amplifier

    DEFF Research Database (Denmark)

    Marschall, Sebastian; Klein, Thomas; Wieser, Wolfgang

    2010-01-01

    While swept source optical coherence tomography (OCT) in the 1050 nm range is promising for retinal imaging, there are certain challenges. Conventional semiconductor gain media have limited output power, and the performance of high-speed Fourier domain mode-locked (FDML) lasers suffers from...

  15. Optical flip-flop: Based on two-coupled mode-locked ring lasers

    NARCIS (Netherlands)

    Tangdiongga, E.; Yang, X.X.; Li, Z.; Liu, Y.S.; Lenstra, D.; Khoe, G.D.; Dorren, H.J.S.

    2005-01-01

    We report an all-optical flip-flop that is based on two coupled actively mode-locked fiber ring lasers. The lasers are coupled so that when one of the lasers lases, it quenches lasing in the other laser. The state of the flip-flop is determined by the wavelength of the laser that is currently

  16. All-fiber Ho-doped mode-locked oscillator based on a graphene saturable absorber

    Czech Academy of Sciences Publication Activity Database

    Sotor, J.; Pawliszewska, M.; Sobon, G.; Kaczmarek, P.; Przewolka, A.; Pasternak, I.; Cajzl, Jakub; Peterka, Pavel; Honzátko, Pavel; Kašík, Ivan; Strupinski, W.; Abramski, K.

    2016-01-01

    Roč. 41, č. 11 (2016), s. 2592-2595 ISSN 0146-9592 R&D Projects: GA ČR GA14-35256S; GA MŠk(CZ) LD15122 Institutional support: RVO:67985882 Keywords : Fiber lasers * Graphene * Mode-locked oscillators Subject RIV: BH - Optics , Masers, Lasers Impact factor: 3.416, year: 2016

  17. Effects of resonator input power on Kerr lens mode-locked lasers

    Indian Academy of Sciences (India)

    Abstract. Using the ABCD matrix method, the common stability region between the sagittal and tangential planes of a four-mirror Kerr lens mode-locked (KLM) laser cavity is obtained for different ranges of input power. In addition, the effect of the input power on the Kerr lens sensitivity is investigated. Optimal input power and ...

  18. Nanoscale charcoal powder induced saturable absorption and mode-locking of a low-gain erbium-doped fiber-ring laser

    International Nuclear Information System (INIS)

    Lin, Yung-Hsiang; Chi, Yu-Chieh; Lin, Gong-Ru

    2013-01-01

    Triturated charcoal nano-powder directly brushed on a fiber connector end-face is used for the first time as a fast saturable absorber for a passively mode-locked erbium-doped fiber-ring laser (EDFL). These dispersant-free charcoal nano-powders with a small amount of crystalline graphene phase and highly disordered carbon structure exhibit a broadened x-ray diffraction peak and their Raman spectrum shows the existence of a carbon related D-band at 1350 cm −1 and the disappearance of the 2D-band peak at 2700 cm −1 . The charcoal nano-powder exhibits a featureless linear absorbance in the infrared region with its linear transmittance of 0.66 nonlinearly saturated at 0.73 to give a ΔT/T of 10%. Picosecond mode-locking at a transform-limited condition of a low-gain EDFL is obtained by using the charcoal nano-powder. By using a commercial EDFA with a linear gain of only 17 dB at the saturated output power of 17.5 dB m required to initiate the saturable absorption of the charcoal nano-powder, the EDFL provides a pulsewidth narrowing from 3.3 to 1.36 ps associated with its spectral linewidth broadening from 0.8 to 1.83 nm on increasing the feedback ratio from 30 to 90%. This investigation indicates that all the carbon-based materials containing a crystalline graphene phase can be employed to passively mode-lock the EDFL, however, the disordered carbon structure inevitably induces a small modulation depth and a large mode-locking threshold, thus limiting the pulsewidth shortening. Nevertheless, the nanoscale charcoal passively mode-locked EDFL still shows the potential to generate picosecond pulses under a relatively low cavity gain. An appropriate cavity design can be used to compensate this defect-induced pulsewidth limitation and obtain a short pulsewidth. (letter)

  19. 10-GHz 1.59-μm quantum dash passively mode-locked two-section lasers

    DEFF Research Database (Denmark)

    Dontabactouny, Madhoussoudhana; Rosenberg, C.; Semenova, Elizaveta

    2010-01-01

    This paper reports the fabrication and the characterisation of a 10 GHz two-section passively mode-locked quantum dash laser emitting at 1.59 μm. The potential of the device's mode-locking is investigated through an analytical model taking into account both the material parameters and the laser...

  20. Systematic investigation of the temperature behavior of InAs/InP quantum nanostructure passively mode-locked lasers

    DEFF Research Database (Denmark)

    Klaime, K.; Piron, R.; Grillot, F.

    2013-01-01

    for the first time a systematic investigation of the temperature-dependence on the mode-locking properties of InAs/InP QN devices. Beside, a rigorous comparison between QDashes and QDs temperature dependence is proposed through a proper analysis of the mode-locking stability maps. Experimental results also show...

  1. Passively Q-switched and mode-locked Nd:GGG laser with a Bi-doped GaAs saturable absorber.

    Science.gov (United States)

    Cong, Wen; Li, Dechun; Zhao, Shengzhi; Yang, Kejian; Li, Xiangyang; Qiao, Hui; Liu, Ji

    2014-06-16

    A simultaneously passively Q-switched and mode-locked (QML) Nd:GGG laser using a Bi-doped GaAs wafer as saturable absorber is accomplished for the first time. The Bi-doped GaAs wafer is fabricated by ion implantation and subsequent annealing. In comparison to the passively QML laser with GaAs, the QML laser with Bi-doped GaAs can generate more stable pulses with 99% modulation depth. The experiment results indicate that the Bi-doped GaAs could be an excellent saturable absorber for diode-pumped QML lasers.

  2. Design optimization of a compact photonic crystal microcavity based on slow light and dispersion engineering for the miniaturization of integrated mode-locked lasers

    Directory of Open Access Journals (Sweden)

    Malik Kemiche

    2018-01-01

    Full Text Available We exploit slow light (high ng modes in planar photonic crystals in order to design a compact cavity, which provides an attractive path towards the miniaturization of near-infrared integrated fast pulsed lasers. By applying dispersion engineering techniques, we can design structures with a low dispersion, as needed by mode-locking operation. Our basic InP SiO2 heterostructure is robust and well suited to integrated laser applications. We show that an optimized 30 μm long cavity design yields 9 frequency-equidistant modes with a FSR of 178 GHz within a 11.5 nm bandwidth, which could potentially sustain the generation of optical pulses shorter than 700 fs. In addition, the numerically calculated quality factors of these modes are all above 10,000, making them suitable for reaching laser operation. Thanks to the use of a high group index (28, this cavity design is almost one order of magnitude shorter than standard rib-waveguide based mode-locked lasers. The use of slow light modes in planar photonic crystal based cavities thus relaxes the usual constraints that tightly link the device size and the quality (peak power, repetition rate of the pulsed laser signal.

  3. Quasiperiodicity, mode-locking, and universal scaling in Rayleigh-Benard convection

    International Nuclear Information System (INIS)

    Ecke, R.E.

    1990-01-01

    This major review paper describes research on a model nonlinear dynamical system of small-aspect-ratio Rayleigh-Benard convection in 3 He - 4 He mixtures. The nonlinear effects of mode locking and quasiperiodic behavior are described. Analysis techniques for characterizing the state of the dynamical system include Fourier transforms, Poincare sections, phase differences, transients, multifractal f(∝) spectra and scaling function dynamics. Theoretical results such as the fractal staircase of mode-locked intervals and the Arnold tongues are reproduced in experimental data. New techniques for analyzing scaling dynamics are developed and discussed. This is a tutorial article that introduces the major important concepts in nonlinear dynamics and focuses on experimental problems and techniques. 77 refs

  4. Ultrathin quartz plate-based multilayer MoS2 for passively mode-locked fiber lasers (invited)

    Science.gov (United States)

    Jiang, Zike; Li, Jiarong; Chen, Hao; Wang, Jinzhang; Zhang, Wenfei; Yan, Peiguang

    2018-01-01

    We have grown ultrathin quartz plate-based multilayer molybdenum disulfide (MoS2) by chemical vapor deposition (CVD). When employed as saturable absorber (SA), the prepared MoS2 device exhibits remarkable merits (e.g. uniform thickness, high quality of crystal lattice high damage threshold easy fabrication and good practicability). The modulation depth, saturable intensity, and non-saturable loss of this SA device are measured to be 16.1%, 0.438 MW/cm2 and 44.6% respectively. By incorporating the SA into a typical ring cavity erbium-doped fiber laser, stable passive soliton mode-locked pulse is achieved with the repetition frequency of 0.987 MHz, the signal noise ratio (SNR) of 71.4 dB and the pulse duration of 2.17 ps. The experimental results demonstrate our MoS2-SA device to be an effective mode locker, and it is promising to be used in ultrafast photonics.

  5. MHD stability and mode locking in pre-disruptive plasmas on TORE SUPRA

    International Nuclear Information System (INIS)

    Vallet, J.C.; Edery, D.; Joffrin, E.; Lecoustey, P.; Mohamed-Benkadda, M.S.; Pecquet, A.L.; Samain, A.; Talvard, M.

    1991-01-01

    Experiments devoted to the study of MHD activity have been carried out on TORE SUPRA. The observed disruptions are preceded by the growth of an m=2 N=1 rotating mode which locks when the magnetic field perturbation exceeds a critical value. The mode locking is interpreted as a bifurcation of the mode frequency. In addition, stabilization of the m=2 N=1 tearing mode has been obtained with the Ergodic Divertor (ED)

  6. Universal soliton pattern formations in passively mode-locked fiber lasers.

    Science.gov (United States)

    Amrani, Foued; Salhi, Mohamed; Grelu, Philippe; Leblond, Hervé; Sanchez, François

    2011-05-01

    We investigate multiple-soliton pattern formations in a figure-of-eight passively mode-locked fiber laser. Operation in the anomalous dispersion regime with a double-clad fiber amplifier allows generation of up to several hundreds of solitons per round trip. We report the observation of remarkable soliton distributions: soliton gas, soliton liquid, soliton polycrystal, and soliton crystal, thus indicating the universality of such complexes.

  7. Reduction of timing jitter and intensity noise in normal-dispersion passively mode-locked fiber lasers by narrow band-pass filtering.

    Science.gov (United States)

    Qin, Peng; Song, Youjian; Kim, Hyoji; Shin, Junho; Kwon, Dohyeon; Hu, Minglie; Wang, Chingyue; Kim, Jungwon

    2014-11-17

    Fiber lasers mode-locked with normal cavity dispersion have recently attracted great attention due to large output pulse energy and femtosecond pulse duration. Here we accurately characterized the timing jitter of normal-dispersion fiber lasers using a balanced cross-correlation method. The timing jitter characterization experiments show that the timing jitter of normal-dispersion mode-locked fiber lasers can be significantly reduced by using narrow band-pass filtering (e.g., 7-nm bandwidth filtering in this work). We further identify that the timing jitter of the fiber laser is confined in a limited range, which is almost independent of cavity dispersion map due to the amplifier-similariton formation by insertion of the narrow bandpass filter. The lowest observed timing jitter reaches 0.57 fs (rms) integrated from 10 kHz to 10 MHz Fourier frequency. The rms relative intensity noise (RIN) is also reduced from 0.37% to 0.02% (integrated from 1 kHz to 5 MHz Fourier frequency) by the insertion of narrow band-pass filter.

  8. Fiber optical parametric oscillator based on photonic crystal fiber pumped with all-normal-dispersion mode-locked Yb:fiber laser

    International Nuclear Information System (INIS)

    Gou Dou-Dou; Yang Si-Gang; Zhang Lei; Wang Xiao-Jian; Chen Hong-Wei; Chen Ming-Hua; Xie Shi-Zhong; Chen Wei; Luo Wen-Yong

    2014-01-01

    We demonstrate a cost effective, linearly tunable fiber optical parametric oscillator based on a home-made photonic crystal fiber pumped with a mode-locked ytterbium-doped fiber laser, providing linely tuning ranges from 1018 nm to 1038 nm for the idler wavelength and from 1097 nm to 1117 nm for the signal wavelength by tuning the pump wavelength and the cavity length. In order to obtain the desired fiber with a zero dispersion wavelength around 1060 nm, eight samples of photonic crystal fibers with gradually changed structural parameters are fabricated for the reason that it is difficult to accurately customize the structural dimensions during fabrication. We verify the usability of the fabricated fiber experimentally via optical parametric generation and conclude a successful procedure of design, fabirication, and verification. A seed source of home-made all-normal-dispersion mode-locked ytterbium-doped fiber laser with 38.57 ps pulsewidth around the 1064 nm wavelength is used to pump the fiber optical parametric oscillator. The wide picosecond pulse pump laser enables a larger walk-off tolerance between the pump light and the oscillating light as well as a longer photonic crystal fiber of 20 m superior to the femtosecond pulse lasers, resulting in a larger parametric amplification and a lower threshold pump power of 15.8 dBm of the fiber optical parametric oscillator. (electromagnetism, optics, acoustics, heat transfer, classical mechanics, and fluid dynamics)

  9. Passively mode-locked fiber laser based on a hollow-core photonic crystal fiber filled with few-layered graphene oxide solution.

    Science.gov (United States)

    Liu, Zhi-Bo; He, Xiaoying; Wang, D N

    2011-08-15

    We demonstrate a nanosecond-pulse erbium-doped fiber laser that is passively mode locked by a hollow-core photonic crystal fiber filled with few-layered graphene oxide solution. Owing to the good solution processing capability of few-layered graphene oxide, which can be filled into the core of a hollow-core photonic crystal fiber through a selective hole filling process, a graphene saturable absorber can be successfully fabricated. The output pulses obtained have a center wavelength, pulse width, and repetition rate of 1561.2 nm, 4.85 ns, and 7.68 MHz, respectively. This method provides a simple and efficient approach to integrate the graphene into the optical fiber system. © 2011 Optical Society of America

  10. Coupled opto electronic oscillator with a passively mode locked extended cavity diode laser

    Energy Technology Data Exchange (ETDEWEB)

    Lee, Jeongmin; Jang, Gwang Hoon; Yoon, Duseong; Song, Minsoo; Yoon, Tai Hyun [Korea Univ., Seoul (Korea, Republic of)

    2008-11-15

    An opto electronic oscillator(OEO)has very unique properties compared to the conventional quartz based microwave oscillators in that its oscillation frequency is determined by the beat note frequency of a phase coherent optical frequency comb generated as a side bands to an optical single mode carrier by using an electro optic modulator (EOM)or a direct current modulation of a semiconductor laser. Recently, a different type of OEO called a COEO has been demonstrated, where the optical carrier in the OEO system has been replaced by a mode locked laser so that an EOM or a direct current modulation are no longer necessary, but has potentially a much lower phase noise thanks to the high Q value of the optical frequency comb due to the mode locking mechanism. In this paper, we propose and demonstrate a COEO based on a passively mode locked ECDL at 852nm in which the fourth harmonic of the repetition frequency of the ECDL matched exactly the ground state hyperfine splitting frequency of the Cs atoms.

  11. Coupled opto electronic oscillator with a passively mode locked extended cavity diode laser

    International Nuclear Information System (INIS)

    Lee, Jeongmin; Jang, Gwang Hoon; Yoon, Duseong; Song, Minsoo; Yoon, Tai Hyun

    2008-01-01

    An opto electronic oscillator(OEO)has very unique properties compared to the conventional quartz based microwave oscillators in that its oscillation frequency is determined by the beat note frequency of a phase coherent optical frequency comb generated as a side bands to an optical single mode carrier by using an electro optic modulator (EOM)or a direct current modulation of a semiconductor laser. Recently, a different type of OEO called a COEO has been demonstrated, where the optical carrier in the OEO system has been replaced by a mode locked laser so that an EOM or a direct current modulation are no longer necessary, but has potentially a much lower phase noise thanks to the high Q value of the optical frequency comb due to the mode locking mechanism. In this paper, we propose and demonstrate a COEO based on a passively mode locked ECDL at 852nm in which the fourth harmonic of the repetition frequency of the ECDL matched exactly the ground state hyperfine splitting frequency of the Cs atoms

  12. Silicon Photonics Transmitter with SOA and Semiconductor Mode-Locked Laser.

    Science.gov (United States)

    Moscoso-Mártir, Alvaro; Müller, Juliana; Hauck, Johannes; Chimot, Nicolas; Setter, Rony; Badihi, Avner; Rasmussen, Daniel E; Garreau, Alexandre; Nielsen, Mads; Islamova, Elmira; Romero-García, Sebastián; Shen, Bin; Sandomirsky, Anna; Rockman, Sylvie; Li, Chao; Sharif Azadeh, Saeed; Lo, Guo-Qiang; Mentovich, Elad; Merget, Florian; Lelarge, François; Witzens, Jeremy

    2017-10-24

    We experimentally investigate an optical link relying on silicon photonics transmitter and receiver components as well as a single section semiconductor mode-locked laser as a light source and a semiconductor optical amplifier for signal amplification. A transmitter based on a silicon photonics resonant ring modulator, an external single section mode-locked laser and an external semiconductor optical amplifier operated together with a standard receiver reliably supports 14 Gbps on-off keying signaling with a signal quality factor better than 7 for 8 consecutive comb lines, as well as 25 Gbps signaling with a signal quality factor better than 7 for one isolated comb line, both without forward error correction. Resonant ring modulators and Germanium waveguide photodetectors are further hybridly integrated with chip scale driver and receiver electronics, and their co-operability tested. These experiments will serve as the basis for assessing the feasibility of a silicon photonics wavelength division multiplexed link relying on a single section mode-locked laser as a multi-carrier light source.

  13. 41 GHz and 10.6 GHz low threshold and low noise InAs/InP quantum dash two-section mode-locked lasers in L band

    DEFF Research Database (Denmark)

    Dontabactouny, M.; Piron, R.; Klaime, K.

    2012-01-01

    This paper reports recent results on InAs/InP quantum dash-based, two-section, passively mode-locked lasers pulsing at 41 GHz and 10.6 GHz and emitting at 1.59 mu m at 20 degrees C. The 41-GHz device (1 mm long) starts lasing at 25 mA under uniform injection and the 10.6 GHz (4 mm long) at 71 m...

  14. Diode array pumped, non-linear mirror Q-switched and mode-locked ...

    Indian Academy of Sciences (India)

    to control the air dispersion of the FW and SH beam by introducing proper phase shift between them and to achieve the maximum loss modulation. The laser output power at .... pulse train as a faithful replica of the fundamental train. But the correspondence between the central peak of the fundamental and that of the SH is ...

  15. Integrated Microwave Photonic Isolators: Theory, Experimental Realization and Application in a Unidirectional Ring Mode-Locked Laser Diode

    Directory of Open Access Journals (Sweden)

    Martijn J.R. Heck

    2015-09-01

    Full Text Available A novel integrated microwave photonic isolator is presented. It is based on the timed drive of a pair of optical modulators, which transmit a pulsed or oscillating optical signal with low loss, when driven in phase. A signal in the reverse propagation direction will find the modulators out of phase and, hence, will experience high loss. Optical and microwave isolation ratios were simulated to be in the range up to 10 dB and 20 dB, respectively, using parameters representative for the indium phosphide platform. The experimental realization of this device in the hybrid silicon platform showed microwave isolation in the 9 dB–22 dB range. Furthermore, we present a design study on the use of these isolators inside a ring mode-locked laser cavity. Simulations show that unidirectional operation can be achieved, with a 30–50-dB suppression of the counter propagating mode, at limited driving voltages. The potentially low noise and feedback-insensitive operation of such a laser makes it a very promising candidate for use as on-chip microwave or comb generators.

  16. DWDM channel spacing tunable optical TDM carrier from a mode-locked weak-resonant-cavity Fabry-Perot laser diode based fiber ring.

    Science.gov (United States)

    Peng, Guo-Hsuan; Chi, Yu-Chieh; Lin, Gong-Ru

    2008-08-18

    A novel optical TDM pulsed carrier with tunable mode spacing matching the ITU-T defined DWDM channels is demonstrated, which is generated from an optically injection-mode-locked weak-resonant-cavity Fabry-Perot laser diode (FPLD) with 10%-end-facet reflectivity. The FPLD exhibits relatively weak cavity modes and a gain spectral linewidth covering >33.5 nm. The least common multiple of the mode spacing determined by both the weak-resonant-cavity FPLD and the fiber-ring cavity can be tunable by adjusting length of the fiber ring cavity or the FPLD temperature to approach the desired 200GHz DWDM channel spacing of 1.6 nm. At a specific fiber-ring cavity length, such a least-common- multiple selection rule results in 12 lasing modes between 1532 and 1545 nm naturally and a mode-locking pulsewidth of 19 ps broadened by group velocity dispersion among different modes. With an additional intracavity bandpass filter, the operating wavelength can further extend from 1520 to 1553.5 nm. After channel filtering, each selected longitudinal mode gives rise to a shortened pulsewidth of 12 ps due to the reduced group velocity dispersion. By linear dispersion compensating with a 55-m long dispersion compensation fiber (DCF), the pulsewidth can be further compressed to 8 ps with its corresponding peak-to-peak chirp reducing from 9.7 to 4.3 GHz.

  17. Passive mode locking in a multisegment laser diode with an external cavity

    International Nuclear Information System (INIS)

    Andreeva, E V; Magnitskiy, Sergey A; Koroteev, Nikolai I; Salik, E; Feinberg, J; Starodubov, D S; Shramenko, M V; Yakubovich, S D

    1999-01-01

    The structure and operating conditions of multisegment laser (GaAl)As diodes with passive locking of the modes of an external cavity (bulk and fibre) were optimised. Regular trains of optical single pulses of picosecond duration were generated in a spectral range 850 - 860 nm. The peak power of these pulses was several watts and the repetition rate was near 1 GHz. Under certain conditions these output pulses were linearly chirped, i.e. they were suitable for subpicosecond time compression. Laboratory prototypes were made of miniature light-emitting modules with these characteristics. (lasers)

  18. Dispersive-cavity actively mode-locked fiber laser for stable radio frequency delivery

    International Nuclear Information System (INIS)

    Dai, Yitang; Wang, Ruixin; Yin, Feifei; Xu, Kun; Li, Jianqiang; Lin, Jintong

    2013-01-01

    We report a novel technique for highly stable transfer of a radio frequency (RF) comb over long optical fiber link, which is highly dispersive and is a part of an actively mode-locked fiber laser. Phase fluctuation along the fiber link, which is mainly induced by physical vibration and temperature fluctuations, is automatically compensated by the self-adapted wavelength shifting. Without phase-locking loop or any tunable parts, stable radio frequency is transferred over a 2-km fiber link, with a time jitter suppression ratio larger than 110. (letter)

  19. Swept source optical coherence microscopy using a Fourier domain mode-locked laser.

    Science.gov (United States)

    Huang, Shu-Wei; Aguirre, Aaron D; Huber, Robert A; Adler, Desmond C; Fujimoto, James G

    2007-05-14

    Swept source optical coherence microscopy (OCM) enables cellular resolution en face imaging as well as integration with optical coherence tomography (OCT) cross sectional imaging. A buffered Fourier domain mode-locked (FDML) laser light source provides high speed, three dimensional imaging. Image resolutions of 1.6 microm x 8 microm (transverse x axial) with a 220 microm x 220 microm field of view and sensitivity higher than 98 dB are achieved. Three dimensional cellular imaging is demonstrated in vivo in the Xenopus laevis tadpole and ex vivo in the rat kidney and human colon.

  20. Self-mode-locking operation of a diode-end-pumped Tm:YAP laser with watt-level output power

    Science.gov (United States)

    Zhang, Su; Zhang, Xinlu; Huang, Jinjer; Wang, Tianhan; Dai, Junfeng; Dong, Guangzong

    2018-03-01

    We report on a high power continuous wave (CW) self-mode-locked Tm:YAP laser pumped by a 792 nm laser diode. Without any additional mode-locking elements in the cavity, stable and self-starting mode-locking operation has been realized. The threshold pump power of the CW self-mode-locked Tm:YAP laser is only 5.4 W. The maximum average output power is as high as 1.65 W at the pump power of 12 W, with the repetition frequency of 468 MHz and the center wavelength of 1943 nm. To the best of our knowledge, this is the first CW self-mode-locked Tm:YAP laser. The experiment results show that the Tm:YAP crystal is a promising gain medium for realizing the high power self-mode-locking operation at 2 µm.

  1. Pulse Characteristics of Passively Mode-Locked Quantum Dot Lasers (Postprint)

    Science.gov (United States)

    2010-07-01

    wide, 1.8-m deep ridges by inductively coupled plasma (ICP) etching in BCl3. Then a BCB layer was applied for isolation between the p-type metal and...GaAs substrate and annealed at 380C for 1 minute to form the n-ohmic contact. A temperature greater than 380C can crack the BCB . Another Ti/Au metal

  2. A dual-loss-modulated intra-cavity frequency-doubled Q-switched and mode-locked Nd:Lu0.15Y0.85VO4/KTP green laser with a single-walled carbon nanotube saturable absorber and an acousto-optic modulator

    International Nuclear Information System (INIS)

    Zhang, Gang; Zhao, Shengzhi; Yang, Kejian; Li, Guiqiu; Li, Dechun; Cheng, Kang; Han, Chao; Zhao, Bin; Wang, Yonggang

    2011-01-01

    By using both a single-walled carbon nanotube saturable absorber (SWCNT-SA) and an acousto-optic (AO) modulator, a dual-loss-modulated intra-cavity frequency-doubled Q-switched and mode-locked (QML) Nd:Lu 0.15 Y 0.85 VO 4 /KTP (KTiOPO 4 ) green laser was demonstrated for the first time. The QML green laser characteristics such as the pulse width and single-pulse energy have been measured for different modulation frequencies of the AO modulator (f p ). In particular, in comparison with the solely passively QML green laser with an SWCNT-SA, the dual-loss-modulated QML green laser can generate a more stable pulse train, a shorter pulse width of the Q-switched envelope, a greater pulse energy and a higher average peak power. For the dual-loss-modulated QML green laser, at a pump power of 7.9 W and a repetition rate of 10 kHz, the pulse width and the pulse energy of the Q-switch envelope and the average peak power of the QML green laser are 50 ns, 20.34 µJ and 15.5 kW, respectively, corresponding to a pulse width compression of 77%, a pulse energy improvement factor of six times and a QML peak power increase factor of 16 times when compared with those for the solely passively QML green laser. The experimental results show that the dual-loss modulation is an efficient method for the generation of a stable QML green laser with an SWCNT-SA

  3. Report on first masing and single mode locking in a prebunched beam FEM oscillator

    Energy Technology Data Exchange (ETDEWEB)

    Cohen, M.; Eichenbaum, A.; Kleinman, H. [Tel-Aviv Univ., Ramat-Aviv (Israel)] [and others

    1995-12-31

    Radiation characteristics of a table-top free electron maser (FEM) are described in this paper. The FEM employs a prebunched electron beam and is operated as an oscillator in the low-gain collective (Raman) regime. Using electron beam prebunching single mode locking at any one of the possible oscillation modes was obtained. The electron beam is prebunched by a microwave tube section before it is injected into the wiggler. By tuning the electron beam bunching frequency, the FEM oscillation frequency can be locked to any eigen frequency of the resonant waveguide cavity which is within the frequency band of net gain of the FEM. The oscillation build up process is sped up, when the FEM operates with a prebunched electron beam, and the build-up time of radiation is shortened significantly. First measurements of masing with and without prebunching and characterization of the emitted radiation are reported.

  4. Mode locking and quasiperiodicity in a discrete-time Chialvo neuron model

    Science.gov (United States)

    Wang, Fengjuan; Cao, Hongjun

    2018-03-01

    The two-dimensional parameter spaces of a discrete-time Chialvo neuron model are investigated. Our studies demonstrate that for all our choice of two parameters (i) the fixed point is destabilized via Neimark-Sacker bifurcation; (ii) there exist mode locking structures like Arnold tongues and shrimps, with periods organized in a Farey tree sequence, embedded in quasiperiodic/chaotic region. We determine analytically the location of the parameter sets where Neimark-Sacker bifurcation occurs, and the location on this curve where Arnold tongues of arbitrary period are born. Properties of the transition that follows the so-called two-torus from quasiperiodicity to chaos are presented clearly and proved strictly by using numerical simulations such as bifurcation diagrams, the largest Lyapunov exponent diagram on MATLAB and C++.

  5. Electronic frequency tuning of the acousto-optic mode-locking device of a laser

    Science.gov (United States)

    Magdich, L. N.; Balakshy, V. I.; Mantsevich, S. N.

    2017-11-01

    The effect of the electronic tuning of the acoustic resonances in an acousto-optic mode-locking device of a laser is investigated theoretically and experimentally. The problem of the excitation of a Fabry-Perot acoustic resonator by a plate-like piezoelectric transducer (PET) is solved in the approximation of plane acoustic waves taking into consideration the actual parameters of an RF generator and the elements for matching the PET to the generator. Resonances are tuned by changing the matching inductance that was connected in parallel to the transducer of the acousto-optic cell. The cell used in the experiment was manufactured from fused silica and included a lithium niobate PET. Changes in the matching inductance in the range of 0.025 to 0.2 μH provided the acoustic-resonance frequency tuning by 0.19 MHz, which exceeds the acoustic- resonance half-width.

  6. A Theoretical Investigation of Mode-Locking Phenomena in Reversed Field Pinches

    International Nuclear Information System (INIS)

    Richard Fitzpatrick

    2004-01-01

    OAK-B135 This paper investigates the formation and breakup of the ''slinky mode'' in an RFP using analytic techniques previously employed to examine mode locking phenomena in tokamaks. The slinky mode is a toroidally localized, coherent interference pattern in the magnetic field which co-rotates with the plasma at the reversal surface. This mode forms, as a result of the nonlinear coupling of multiple m = 1 core tearing modes, via a bifurcation which is similar to that by which toroidally coupled tearing modes lock together in a tokamak. The slinky mode breaks up via a second bifurcation which is similar to that by which toroidally coupled tearing modes in a tokamak unlock. However, the typical m = 1 mode amplitude below which slinky breakup is triggered is much smaller than that above which slinky formation occurs. Analytic expressions for the slinky formation and breakup thresholds are obtained in all regimes of physical interest. The locking of the slinky mode to a static error-field is also investigated analytically. Either the error-field arrests the rotation of the plasma at the reversal surface before the formation of the slinky mode, so that the mode subsequently forms as a non-rotating mode, or the slinky mode forms as a rotating mode and subsequently locks to the error-field. Analytic expressions for the locking and unlocking thresholds are obtained in all regimes of physical interest. The problems associated with a locked slinky mode can be alleviated by canceling out the accidentally produced error-field responsible for locking the slinky mode, using a deliberately created ''control'' error-field. Alternatively, the locking angle of the slinky mode can be swept toroidally by rotating the control field

  7. A theoretical investigation of mode-locking phenomena in reversed field pinches

    Energy Technology Data Exchange (ETDEWEB)

    Richard Fitzpatrick

    2004-03-17

    OAK-B135 This paper investigates the formation and breakup of the ''slinky mode'' in an RFP using analytic techniques previously employed to examine mode locking phenomena in tokamaks. The slinky mode is a toroidally localized, coherent interference pattern in the magnetic field which co-rotates with the plasma at the reversal surface. This mode forms, as a result of the nonlinear coupling of multiple m = 1 core tearing modes, via a bifurcation which is similar to that by which toroidally coupled tearing modes lock together in a tokamak. The slinky mode breaks up via a second bifurcation which is similar to that by which toroidally coupled tearing modes in a tokamak unlock. However, the typical m = 1 mode amplitude below which slinky breakup is triggered is much smaller than that above which slinky formation occurs. Analytic expressions for the slinky formation and breakup thresholds are obtained in all regimes of physical interest. The locking of the slinky mode to a static error-field is also investigated analytically. Either the error-field arrests the rotation of the plasma at the reversal surface before the formation of the slinky mode, so that the mode subsequently forms as a non-rotating mode, or the slinky mode forms as a rotating mode and subsequently locks to the error-field. Analytic expressions for the locking and unlocking thresholds are obtained in all regimes of physical interest. The problems associated with a locked slinky mode can be alleviated by canceling out the accidentally produced error-field responsible for locking the slinky mode, using a deliberately created ''control'' error-field. Alternatively, the locking angle of the slinky mode can be swept toroidally by rotating the control field.

  8. A Theoretical Investigation of Mode-Locking Phenomena in Reversed Field Pinches

    Energy Technology Data Exchange (ETDEWEB)

    Richard Fitzpatrick

    2004-04-07

    OAK-B135 This paper investigates the formation and breakup of the ''slinky mode'' in an RFP using analytic techniques previously employed to examine mode locking phenomena in tokamaks. The slinky mode is a toroidally localized, coherent interference pattern in the magnetic field which co-rotates with the plasma at the reversal surface. This mode forms, as a result of the nonlinear coupling of multiple m = 1 core tearing modes, via a bifurcation which is similar to that by which toroidally coupled tearing modes lock together in a tokamak. The slinky mode breaks up via a second bifurcation which is similar to that by which toroidally coupled tearing modes in a tokamak unlock. However, the typical m = 1 mode amplitude below which slinky breakup is triggered is much smaller than that above which slinky formation occurs. Analytic expressions for the slinky formation and breakup thresholds are obtained in all regimes of physical interest. The locking of the slinky mode to a static error-field is also investigated analytically. Either the error-field arrests the rotation of the plasma at the reversal surface before the formation of the slinky mode, so that the mode subsequently forms as a non-rotating mode, or the slinky mode forms as a rotating mode and subsequently locks to the error-field. Analytic expressions for the locking and unlocking thresholds are obtained in all regimes of physical interest. The problems associated with a locked slinky mode can be alleviated by canceling out the accidentally produced error-field responsible for locking the slinky mode, using a deliberately created ''control'' error-field. Alternatively, the locking angle of the slinky mode can be swept toroidally by rotating the control field.

  9. A theoretical investigation of mode-locking phenomena in reversed field pinches

    International Nuclear Information System (INIS)

    Richard Fitzpatrick

    2004-01-01

    OAK-B135 This paper investigates the formation and breakup of the ''slinky mode'' in an RFP using analytic techniques previously employed to examine mode locking phenomena in tokamaks. The slinky mode is a toroidally localized, coherent interference pattern in the magnetic field which co-rotates with the plasma at the reversal surface. This mode forms, as a result of the nonlinear coupling of multiple m = 1 core tearing modes, via a bifurcation which is similar to that by which toroidally coupled tearing modes lock together in a tokamak. The slinky mode breaks up via a second bifurcation which is similar to that by which toroidally coupled tearing modes in a tokamak unlock. However, the typical m = 1 mode amplitude below which slinky breakup is triggered is much smaller than that above which slinky formation occurs. Analytic expressions for the slinky formation and breakup thresholds are obtained in all regimes of physical interest. The locking of the slinky mode to a static error-field is also investigated analytically. Either the error-field arrests the rotation of the plasma at the reversal surface before the formation of the slinky mode, so that the mode subsequently forms as a non-rotating mode, or the slinky mode forms as a rotating mode and subsequently locks to the error-field. Analytic expressions for the locking and unlocking thresholds are obtained in all regimes of physical interest. The problems associated with a locked slinky mode can be alleviated by canceling out the accidentally produced error-field responsible for locking the slinky mode, using a deliberately created ''control'' error-field. Alternatively, the locking angle of the slinky mode can be swept toroidally by rotating the control field

  10. Mode-locking neurodynamics predict human auditory brainstem responses to musical intervals.

    Science.gov (United States)

    Lerud, Karl D; Almonte, Felix V; Kim, Ji Chul; Large, Edward W

    2014-02-01

    The auditory nervous system is highly nonlinear. Some nonlinear responses arise through active processes in the cochlea, while others may arise in neural populations of the cochlear nucleus, inferior colliculus and higher auditory areas. In humans, auditory brainstem recordings reveal nonlinear population responses to combinations of pure tones, and to musical intervals composed of complex tones. Yet the biophysical origin of central auditory nonlinearities, their signal processing properties, and their relationship to auditory perception remain largely unknown. Both stimulus components and nonlinear resonances are well represented in auditory brainstem nuclei due to neural phase-locking. Recently mode-locking, a generalization of phase-locking that implies an intrinsically nonlinear processing of sound, has been observed in mammalian auditory brainstem nuclei. Here we show that a canonical model of mode-locked neural oscillation predicts the complex nonlinear population responses to musical intervals that have been observed in the human brainstem. The model makes predictions about auditory signal processing and perception that are different from traditional delay-based models, and may provide insight into the nature of auditory population responses. We anticipate that the application of dynamical systems analysis will provide the starting point for generic models of auditory population dynamics, and lead to a deeper understanding of nonlinear auditory signal processing possibly arising in excitatory-inhibitory networks of the central auditory nervous system. This approach has the potential to link neural dynamics with the perception of pitch, music, and speech, and lead to dynamical models of auditory system development. Copyright © 2013 Elsevier B.V. All rights reserved.

  11. High-speed polarization-sensitive OCT at 1060 nm using a Fourier domain mode-locked swept source

    DEFF Research Database (Denmark)

    Marschall, Sebastian; Torzicky, Teresa; Klein, Thomas

    2012-01-01

    sufficiently large datasets. Here, we demonstrate PS-OCT imaging at 350 kHz A-scan rate using a two-channel PS-OCT system in conjunction with a Fourier domain mode-locked laser. The light source spectrum spans up to 100nm around the water absorption minimum at 1060 nm. By modulating the laser pump current, we...

  12. Method for integrating a train of fast, nanosecond wide pulses

    International Nuclear Information System (INIS)

    Rose, C.R.

    1987-01-01

    This paper describes a method used to integrate a train of fast, nanosecond wide pulses. The pulses come from current transformers in a RF LINAC beamline. Because they are ac signals and have no dc component, true mathematical integration would yield zero over the pulse train period or an equally erroneous value because of a dc baseline shift. The circuit used to integrate the pulse train first stretches the pulses to 35 ns FWHM. The signals are then fed into a high-speed, precision rectifier which restores a true dc baseline for the following stage - a fast, gated integrator. The rectifier is linear over 55dB in excess of 25 MHz, and the gated integrator is linear over a 60 dB range with input pulse widths as short as 16 ns. The assembled system is linear over 30 dB with a 6 MHz input signal

  13. K-space linear Fourier domain mode locked laser and applications for optical coherence tomography.

    Science.gov (United States)

    Eigenwillig, Christoph M; Biedermann, Benjamin R; Palte, Gesa; Huber, Robert

    2008-06-09

    We report on a Fourier Domain Mode Locked (FDML) wavelength swept laser source with a highly linear time-frequency sweep characteristic and demonstrate OCT imaging without k-space resampling prior to Fourier transformation. A detailed theoretical framework is provided and different strategies how to determine the optimum drive waveform of the piezo-electrically actuated optical bandpass-filter in the FDML laser are discussed. An FDML laser with a relative optical frequency deviation ??nu/nu smaller than 8 x10(-5) over a 100 nm spectral bandwidth at 1300 nm is presented, enabling high resolution OCT over long ranging depths. Without numerical time-to-frequency resampling and without spectral apodization a sensitivity roll off of 4 dB over 2 mm, 12.5 dB over 4 mm and 26.5 dB over 1 cm at 3.5 mus sweep duration and 106.6 dB maximum sensitivity at 9.2 mW average power is achieved. The axial resolution in air degrades from 14 to 21 mum over 4 mm imaging depth. The compensation of unbalanced dispersion in the OCT sample arm by an adapted tuning characteristic of the source is demonstrated. Good stability of the system without feedback-control loops is observed over hours.

  14. Reconstruction of Attosecond Pulse Trains Using an Adiabatic Phase Expansion

    International Nuclear Information System (INIS)

    Varju, K.; Gustafsson, E.; Johnsson, P.; Mauritsson, J.; L'Huillier, A.; Mairesse, Y.; Agostini, P.; Breger, P.; Carre, B.; Merdji, H.; Monchicourt, P.; Salieres, P.; Frasinski, L.J.

    2005-01-01

    We propose a new method to reconstruct the electric field of attosecond pulse trains. The phase of the high-order harmonic emission electric field is Taylor expanded around the maximum of the laser pulse envelope in the time domain and around the central harmonic in the frequency domain. Experimental measurements allow us to determine the coefficients of this expansion and to characterize the radiation with attosecond accuracy over a femtosecond time scale. The method gives access to pulse-to-pulse variations along the train, including the timing, the chirp, and the attosecond carrier envelope phase

  15. Hysteresis in the tearing mode locking/unlocking due to resonant magnetic perturbations in EXTRAP T2R

    Science.gov (United States)

    Fridström, R.; Frassinetti, L.; Brunsell, P. R.

    2015-10-01

    The physical mechanisms behind the hysteresis in the tearing mode locking and unlocking to a resonant magnetic perturbation (RMP) are experimentally studied in EXTRAP T2R reversed-field pinch. The experiments show that the electromagnetic and the viscous torque increase with increasing perturbation amplitude until the mode locks to the wall. At the wall-locking, the plasma velocity reduction profile is peaked at the radius where the RMP is resonant. Thereafter, the viscous torque drops due to the relaxation of the velocity in the central plasma. This is the main reason for the hysteresis in the RMP locking and unlocking amplitude. The increased amplitude of the locked tearing mode produces further deepening of the hysteresis. Both experimental results are in qualitative agreement with the model in Fitzpatrick et al (2001 Phys. Plasmas 8 4489)

  16. Frequency Stepped Pulse Train Modulated Wind Sensing Lidar

    DEFF Research Database (Denmark)

    Olesen, Anders Sig; Pedersen, Anders Tegtmeier; Rottwitt, Karsten

    2011-01-01

    In this paper a wind sensing lidar utilizing a Frequency Stepped Pulse Train (FSPT) is demonstrated. One of the advantages in the FSTP lidar is that it enables direct measurement of wind speed as a function of distance from the lidar. Theoretically the FSPT lidar continuously produces measurements...... as is the case with a CW lidar, but at the same time with a spatial resolution, and without the range ambiguity originating from e.g. clouds. The FSPT lidar utilizes a frequency sweeping source for generation of the FSPT. The source generates a pulse train where each pulse has an optical carrier frequency...... of frequency shifts corresponding to a specific distance. The spatial resolution depends on the repetition rate of the pulses in the pulse train. Directional wind measurements are shown and compared to a CW lidar measurement. The carrier to noise ratio of the FSPT lidar compared to a CW lidar is discussed...

  17. Free-standing nano-scale graphite saturable absorber for passively mode-locked erbium doped fiber ring laser

    International Nuclear Information System (INIS)

    Lin, Y-H; Lin, G-R

    2012-01-01

    The free-standing graphite nano-particle located between two FC/APC fiber connectors is employed as the saturable absorber to passively mode-lock the ring-type Erbium-doped fiber laser (EDFL). The host-solvent-free graphite nano-particles with sizes of 300 – 500 nm induce a comparable modulation depth of 54%. The interlayer-spacing and lattice fluctuations of polished graphite nano-particles are observed from the weak 2D band of Raman spectrum and the azimuth angle shift of –0.32 ° of {002}-orientation dependent X-ray diffraction peak. The graphite nano-particles mode-locked EDFL generates a 1.67-ps pulsewidth at linearly dispersion-compensated regime with a repetition rate of 9.1 MHz. The time-bandwidth product of 0.325 obtained under a total intra-cavity group-delay-dispersion of –0.017 ps 2 is nearly transform-limited. The extremely high stability of the nano-scale graphite saturable absorber during mode-locking is observed at an intra-cavity optical energy density of 7.54 mJ/cm 2 . This can be attributed to its relatively high damage threshold (one order of magnitude higher than the graphene) on handling the optical energy density inside the EDFL cavity. The graphite nano-particle with reduced size and sufficient coverage ratio can compete with other fast saturable absorbers such as carbon nanotube or graphene to passively mode-lock fiber lasers with decreased insertion loss and lasing threshold

  18. Rogue waves generation via nonlinear soliton collision in multiple-soliton state of a mode-locked fiber laser.

    Science.gov (United States)

    Peng, Junsong; Tarasov, Nikita; Sugavanam, Srikanth; Churkin, Dmitry

    2016-09-19

    We report for the first time, rogue waves generation in a mode-locked fiber laser that worked in multiple-soliton state in which hundreds of solitons occupied the whole laser cavity. Using real-time spatio-temporal intensity dynamics measurements, it is unveiled that nonlinear soliton collision accounts for the formation of rogue waves in this laser state. The nature of interactions between solitons are also discussed. Our observation may suggest similar formation mechanisms of rogue waves in other systems.

  19. Self-organized compound pattern and pulsation of dissipative solitons in a passively mode-locked fiber laser

    Science.gov (United States)

    Wang, Zhenhong; Wang, Zhi; Liu, Yange; He, Ruijing; Zhao, Jian; Wang, Guangdou; Yang, Guang

    2018-02-01

    We experimentally observe soliton self-organization and pulsation in a passively mode-locked fiber laser. The optomechanical interaction in the optical fiber is key to the formation of equidistant soliton bunches. These solitons simultaneously undergo a pulsation process with a period corresponding to tens of the cavity round trip time. Using the dispersive Fourier transformation technique, we find that the Kelly sidebands in the shot-to-shot spectra appear periodically, synchronizing with the pulsation.

  20. Theoretical description of spontaneous pulse formation in a semiconductor microring laser

    International Nuclear Information System (INIS)

    Gil, L.; Columbo, L.

    2011-01-01

    We theoretically describe the spontaneous formation of stable pulses in a GaAs bulk semiconductor microring laser. These pulses are obtained without active or passive mode locking. We show that the parameter regime associated with their existence is limited on one side by the phase instability of the continuous-wave solution, and on the other side by the failure of Lamb's mode-locking criterion. Bistability between the continuous-wave solution and the spontaneous pulses is observed.

  1. Directly exfoliated and imprinted graphite nano-particle saturable absorber for passive mode-locking erbium-doped fiber laser

    Science.gov (United States)

    Lin, G.-R.; Lin, Y.-C.

    2011-12-01

    By directly brushing and scribing an ultra-thin (face of a FC/APC connector in erbium-doped fiber laser (EDFL), and then imprinting it with the graphite nano-particles exfoliated from a graphite foil, the intra-cavity graphite nano-particle based saturable absorber can be formed to induce passive mode-locking effect in the EDFL. Such a novel approach greatly suppresses the film-thickness induced laser-beam divergent loss to 3.4%, thus enhancing the intra-cavity circulating power to promote the shortening on mode-locking pulsewidth. The saturable absorber with area coverage ratio of graphite nano-particles is detuned from 70 to 25% to provide the modulation depth enhancing from 11 to 20% and the saturated transmittance from 27 to 60%. Optimizing the coverage ratio reduces the non-saturable loss to 40% and enhances the modulation depth to 21%, such that the sub-ps soliton mode-locking can be initiated to provide a chirped pulsewidth of 482 fs and a linewidth of 2.87 nm.

  2. Polarisation Dynamics of Vector Soliton Molecules in Mode Locked Fibre Laser

    Science.gov (United States)

    Tsatourian, Veronika; Sergeyev, Sergey V.; Mou, Chengbo; Rozhin, Alex; Mikhailov, Vitaly; Rabin, Bryan; Westbrook, Paul S.; Turitsyn, Sergei K.

    2013-01-01

    Two fundamental laser physics phenomena - dissipative soliton and polarisation of light are recently merged to the concept of vector dissipative soliton (VDS), viz. train of short pulses with specific state of polarisation (SOP) and shape defined by an interplay between anisotropy, gain/loss, dispersion, and nonlinearity. Emergence of VDSs is both of the fundamental scientific interest and is also a promising technique for control of dynamic SOPs important for numerous applications from nano-optics to high capacity fibre optic communications. Using specially designed and developed fast polarimeter, we present here the first experimental results on SOP evolution of vector soliton molecules with periodic polarisation switching between two and three SOPs and superposition of polarisation switching with SOP precessing. The underlying physics presents an interplay between linear and circular birefringence of a laser cavity along with light induced anisotropy caused by polarisation hole burning. PMID:24193374

  3. Comparison of the noise performance of 10 GHz repetition rate quantum-dot and quantum well monolithic mode-locked semiconductor lasers

    DEFF Research Database (Denmark)

    Carpintero, G.; Thompson, M. G.; Yvind, Kresten

    2011-01-01

    Mode-locked lasers are commonly used in carrier-wave signal generation systems because of their excellent phase noise performance. Owing to the importance of this key parameter, this study presents a like-for-like comparison of the noise performance of the passive mode-locked regime of two devices...... fabricated with different material gain systems, one quantum well and the other quantum dot (QD), both with a monolithic all-active two-section mode-locked structure. Two important factors are identified as having a significant effect on the noise performance, the RF linewidth of the first harmonic...... and the shape of the noise pedestals, both depending on the passive mode-locked bias conditions. Nevertheless, the dominant contribution of the RF linewidth to the phase noise, which is significantly narrower for the QD laser, makes this material more suitable for optical generation of low-noise millimetre...

  4. Time-Grating for the Generation of STUD Pulse Trains

    Science.gov (United States)

    Zheng, Jun; Wang, Shi-Wei; Xu, Jian-Qiu

    2013-04-01

    Spike train of uneven duration or delay (STUD) pulses hold potential for laser-plasma interaction (LPI) control in laser fusion. The technique based on time grating is applied to generate an STUD pulse train. Time grating, a temporal analogy of the diffraction grating, can control the pulse width, shape, and repetition rate easily through the use of electro-optical devices. The pulse width and repetition rate are given by the modulation frequency and depth of the phase modulation function in theory and numerical calculation. The zero-chirped phase modulation is good for the compression effect of the time grating. A principle experiment of two pulses interfering is shown to verify the time grating function.

  5. Modulation of Pulse Train Using Leapfrogging Pulses Developed in Unbalanced Coupled Nonlinear Transmission Lines

    Directory of Open Access Journals (Sweden)

    Koichi Narahara

    2018-01-01

    Full Text Available The leapfrogging pulses in two unbalanced electrical nonlinear transmission lines (NLTLs with capacitive couplings are investigated for efficient modulation of a pulse train. Due to the resonant interactions, the nonlinear solitary waves in the NLTLs exhibit complementary behaviors of amplitudes and phases called leapfrogging. For maximizing resonance, both solitary waves should have a common average velocity. Sharing the common velocity, the characteristic impedance can still be freely designed for two coupled solitary waves. In this study, we characterize the leapfrogging pulses developed in unbalanced NLTLs having distinct characteristic impedance. Through the soliton perturbation theory and numerical time-domain calculations, it is found that both the leapfrogging frequency and the voltage variations of pulse amplitudes increase as the difference in the characteristic impedance becomes large. These properties can improve the on/off ratio of modulated pulse train.

  6. Stimulated Brillouin scattering in dispersion-decreasing fiber with ultrahigh-speed femtosecond soliton pulse compression.

    Science.gov (United States)

    Hirooka, Toshihiko; Ono, Shinpei; Hagiuda, Ken-ichi; Nakazawa, Masataka

    2005-02-15

    We report that stimulated Brillouin scattering (SBS) in a dispersion-decreasing fiber (DDF) is particularly disadvantageous with ultrahigh-speed femtosecond soliton compression that exceeds 40 GHz. It is important to note that the increase in the longitudinal mode power of a soliton is proportional to the square of the repetition rate. The SBS threshold is determined by the dispersion-decreasing rate of the DDF, rather than its fiber loss. We suppressed the SBS by applying 30-MHz frequency modulation to a mode-locked fiber laser and successfully obtained a stable 40-GHz, 100-fs pulse train.

  7. Enhanced diffusion weighting generated by selective adiabatic pulse trains

    Science.gov (United States)

    Sun, Ziqi; Bartha, Robert

    2007-09-01

    A theoretical description and experimental validation of the enhanced diffusion weighting generated by selective adiabatic full passage (AFP) pulse trains is provided. Six phantoms (Ph-1-Ph-6) were studied on a 4 T Varian/Siemens whole body MRI system. Phantoms consisted of 2.8 cm diameter plastic tubes containing a mixture of 10 μm ORGASOL polymer beads and 2 mM Gd-DTPA dissolved in 5% agar (Ph-1) or nickel(II) ammonium sulphate hexahydrate doped (56.3-0.8 mM) water solutions (Ph-2-Ph-6). A customized localization by adiabatic selective refocusing (LASER) sequence containing slice selective AFP pulse trains and pulsed diffusion gradients applied in the phase encoding direction was used to measure 1H 2O diffusion. The b-value associated with the LASER sequence was derived using the Bloch-Torrey equation. The apparent diffusion coefficients measured by LASER were comparable to those measured by a conventional pulsed gradient spin-echo (PGSE) sequence for all phantoms. Image signal intensity increased in Ph-1 and decreased in Ph-2-Ph-6 as AFP pulse train length increased while maintaining a constant echo-time. These experimental results suggest that such AFP pulse trains can enhance contrast between regions containing microscopic magnetic susceptibility variations and homogeneous regions in which dynamic dephasing relaxation mechanisms are dominant.

  8. Attosecond pulse trains generated using two color laser fields

    International Nuclear Information System (INIS)

    Mauritsson, J.; Louisiana State University, Baton Rouge, LA; Johnsson, P.; Gustafsson, E.; L'Hullier, A.; Schafer, K.J.; Gaarde, M.B.

    2006-01-01

    Complete test of publication follows. We present the generation of attosecond pulse trains from a superposition of an infrared (IR) laser field and its second harmonic. Our attosecond pulses are synthesized by selecting a number of synchronized harmonics generated in argon. By adding the second harmonic to the driving field the inversion symmetry of generation process is broken and both odd and even harmonics are generated. Consecutive half cycles in the two color field differ beyond the simple sign change that occurs in a one color field and have very different shapes and amplitudes. This sub-cycle structure of the field, which governs the generation of the attosecond pulses, depends strongly on the relative phase and intensity of the two fields, thereby providing additional control over the generation process. The generation of attosecond pulses is frequently described using the semi-classical three step model where an electron is: (1) ionized through tunneling ionization during one half cycle; (2) reaccelerated back towards the ion core by the next half cycle; where it (3) recombines with the ground-state releasing the access energy in a short burst of light. In the two color field the symmetry between the ionizing and reaccelerating field is broken, which leads to two possible scenarios: the electron can either be ionized during a strong half cycle and reaccelerated by a weaker field or vice versa. The periodicity is a full IR cycle in both cases and hence two trains of attosecond pulses are generated which are offset from each other. The generation efficiency, however, is very different for the two cases since it is determined mainly by the electric field strength at the time of tunneling and one of the trains will therefore dominate the other. We investigate experimentally both the spectral and temporal structure of the generated attosecond pulse trains as a function of the relative phase between the two driving fields. We find that for a wide range of

  9. Effect of interval training programme on pulse pressure in the ...

    African Journals Online (AJOL)

    EB

    2013-09-03

    Sep 3, 2013 ... Abstract. Background: Pulse pressure (PP), might be a stronger determinants of cardiovascular risk. Objective: To investigate the effect of interval training program on PP in subjects with hypertension. Methods: Two hundred and forty five male patients with mild to moderate (Systolic Blood Pressure [SBP] ...

  10. Effect of interval training programme on pulse pressure in the ...

    African Journals Online (AJOL)

    Background: Pulse pressure (PP), might be a stronger determinants of cardiovascular risk. Objective: To investigate the effect of interval training program on PP in subjects with hypertension. Methods: Two hundred and forty five male patients with mild to moderate (Systolic Blood Pressure [SBP] between 140-179 & Diastolic ...

  11. Hand-held pulse-train-analysis instrument

    International Nuclear Information System (INIS)

    Nixon, K.V.; Garcia, C.

    1983-01-01

    A portable hand-held pulse-train-analysis instrument uses a number-oriented microprocessor sequenced by a single component microprocessor. The incorporation of new CMOS integrated circuits makes possible complex analysis in a small, easily operated, battery-powered unit. The instrument solves an immediate problem with threshold setting of plastic scintillators and promises numerous other applications

  12. Hand-held pulse-train-analysis instrument

    International Nuclear Information System (INIS)

    Nixon, K.V.; Garcia, C.

    1982-01-01

    A portable hand-held pulse-train-analysis instrument uses a number-oriented microprocessor sequenced by a single component microprocessor. The incorporation of new CMOS integrated circuits makes possible complex analysis in a small, easily operated, battery-powered unit. The instrument solves an immediate problem with threshold setting of plastic scintillators and promises numerous other applications

  13. On the Possible Origin of Chaotic Pulse Trains in Lightning Flashes

    Directory of Open Access Journals (Sweden)

    Mohd Muzafar Ismail

    2017-02-01

    Full Text Available In this study, electromagnetic field radiation bursts known as chaotic pulse trains (CPTs and regular pulse trains (RPTs generated by lightning flashes were analyzed. Through a numerical analysis it was found that a typical CPT could be generated by superimposing several RPTs onto each other. It is suggested that the chaotic pulse trains are created by a superposition of several regular pulse trains. Since regular pulse trains are probably created by dart or dart-stepped leaders or K-changes inside the cloud, chaotic pulse trains are caused by the superposition of electric fields caused by more than one of these leaders or K-changes propagating simultaneously. The hypothesis is supported by the fact that one can find regular pulse trains either in the beginning, middle or later stages of chaotic pulse trains.

  14. Study of simulations q-switching and mode-locking in Nd:YVO4 laser with Cr4+:YAG crystal

    International Nuclear Information System (INIS)

    Al-Sous, M. B.

    2007-12-01

    A numerical model of rate equations for a four-level solid-state laser with Cr 4+ :YAG saturable absorber including excited state absorption ESA is presented. The cavity is divided into a large number of disks and the model is solved for each disk and its local corresponding photon flux. The flux array is shifted for each recurrence simulating the movement of photons inside the cavity during the round trip. This simulator can describe the mode locking phenomenon and can be used to simulate the simultaneous mode locking and Q-switching with a saturable absorber.(author)

  15. Individual optimization of InAlGaAsP-InP sections for 1.55-μm passively mode-locked lasers

    DEFF Research Database (Denmark)

    Kulkova, Irina; Larsson, David; Semenova, Elizaveta

    2012-01-01

    We present integrated single QW semiconductor optical amplifier and MQW electroabsorber modulator based on InAlGaAsP-InP materials for application in a monolithic mode-locked laser. Optimized structures with high-quality butt-joint interfaces are demonstrated.......We present integrated single QW semiconductor optical amplifier and MQW electroabsorber modulator based on InAlGaAsP-InP materials for application in a monolithic mode-locked laser. Optimized structures with high-quality butt-joint interfaces are demonstrated....

  16. A mode-locked thulium-doped fiber laser based on a nonlinear loop mirror

    Czech Academy of Sciences Publication Activity Database

    Honzátko, Pavel; Baravets, Yauhen; Todorov, Filip

    2013-01-01

    Roč. 10, č. 7 (2013) ISSN 1612-2011 R&D Projects: GA ČR(CZ) GAP205/11/1840 Institutional support: RVO:67985882 Keywords : PULSE GENERATION * RING LASER * OSCILLATOR Subject RIV: BH - Optics, Masers, Lasers Impact factor: 2.964, year: 2013

  17. Vector nature of multi-soliton patterns in a passively mode-locked figure-eight fiber laser.

    Science.gov (United States)

    Ning, Qiu-Yi; Liu, Hao; Zheng, Xu-Wu; Yu, Wei; Luo, Ai-Ping; Huang, Xu-Guang; Luo, Zhi-Chao; Xu, Wen-Cheng; Xu, Shan-Hui; Yang, Zhong-Min

    2014-05-19

    The vector nature of multi-soliton dynamic patterns was investigated in a passively mode-locked figure-eight fiber laser based on the nonlinear amplifying loop mirror (NALM). By properly adjusting the cavity parameters such as the pump power level and intra-cavity polarization controllers (PCs), in addition to the fundamental vector soliton, various vector multi-soliton regimes were observed, such as the random static distribution of vector multiple solitons, vector soliton cluster, vector soliton flow, and the state of vector multiple solitons occupying the whole cavity. Both the polarization-locked vector solitons (PLVSs) and the polarization-rotating vector solitons (PRVSs) were observed for fundamental soliton and each type of multi-soliton patterns. The obtained results further reveal the fundamental physics of multi-soliton patterns and demonstrate that the figure-eight fiber lasers are indeed a good platform for investigating the vector nature of different soliton types.

  18. Real-time full-field characterization of transient dissipative soliton dynamics in a mode-locked laser

    Science.gov (United States)

    Ryczkowski, P.; Närhi, M.; Billet, C.; Merolla, J.-M.; Genty, G.; Dudley, J. M.

    2018-04-01

    Dissipative solitons are remarkably localized states of a physical system that arise from the dynamical balance between nonlinearity, dispersion and environmental energy exchange. They are the most universal form of soliton that can exist, and are seen in far-from-equilibrium systems in many fields, including chemistry, biology and physics. There has been particular interest in studying their properties in mode-locked lasers, but experiments have been limited by the inability to track the dynamical soliton evolution in real time. Here, we use simultaneous dispersive Fourier transform and time-lens measurements to completely characterize the spectral and temporal evolution of ultrashort dissipative solitons as their dynamics pass through a transient unstable regime with complex break-up and collisions before stabilization. Further insight is obtained from reconstruction of the soliton amplitude and phase and calculation of the corresponding complex-valued eigenvalue spectrum. These findings show how real-time measurements provide new insights into ultrafast transient dynamics in optics.

  19. Attosecond pulse trains from long laser-gas interaction targets

    International Nuclear Information System (INIS)

    Hauri, C.P.; Lopez-Martens, R.; Varju, K.; Ruchon, T.; Gustafsson, E.; L'Huillier, A.

    2006-01-01

    Complete test of publication follows. Many experiments in attosecond physics require high XUV photon flux as well as a clean attosecond pulse train (APT) temporal structure. Temporal characterization of high-order harmonic generation (HHG) in long interaction targets is thus of high interest. HHG being a very inefficient process, a large effort has been made to increase the amount of XUV photons emitted per infrared laser pulse. Besides quasi phase-matching in a modulated capillary, loose driving laser focusing conditions and subsequent self-channeling have shown to significantly increase the conversion efficiency. We characterized the temporal structure of APTs generated during the self-channeling of an intense IR driving laser pulse. Our first results indicate, however, that the temporal structure of the APT generated during the HHG process might be affected by quantum path interference and spectral phase distortion due to the self-channeling process itself. In particular, our measurements show that the relative spectral phase between consecutive harmonics can strongly vary depending on the target length and the position of the laser focus with respect to the target. In general for short gas targets, no clean APT structure can be expected since the individual attosecond pulses carry significant chirp. For longer targets, however, we observe a flattening of the harmonic spectral phase, resulting in near-transform-limited attosecond pulse trains. A complete analysis of the process is complex and involves detailed knowledge of the spatial and temporal evolution of the self-channeling driver laser pulse throughout the gas target.

  20. Pulse train induced rotational excitation and orientation of a polar molecule.

    Science.gov (United States)

    Tyagi, Ashish; Arya, Urvashi; Vidhani, Bhavna; Prasad, Vinod

    2014-08-14

    We investigate theoretically the rotational excitation and field free molecular orientation of polar HBr molecule, interacting with train of ultrashort laser pulses. By adjusting the number of pulses, pulse period and the intensity of the pulse, one can suppress a population while simultaneously enhancing the desired population in particular rotational state. We have used train of laser pulses of different shaped pulse envelopes. The dynamics and orientation of molecules in the presence of pulse train of different shapes is studied and explained. Copyright © 2014 Elsevier B.V. All rights reserved.

  1. Control of molecular breakup by an infrared pulse and a femtosecond pulse train

    Science.gov (United States)

    Singh, Kamal P.; Kenfack, A.; Rost, Jan M.; Pfeifer, Thomas

    2018-03-01

    We investigate the dissociation dynamics of diatomic molecules subjected to both a femtosecond infrared (IR) laser pulse and a femtosecond pulse train (FPT) within the framework of the Morse potential model. When the IR and FPT are phase delayed, we observe well-resolved oscillations in dissociation probability, corresponding to multiple integers of the IR period, exhibiting enhancement and suppression of bond dissociation. These oscillations reveal a rich dynamics as a function of the IR and FPT parameters including chaotic fields. A frequency-resolved profile of dressed molecular states shows that these oscillations are due to interference of many quantum paths analogous to the recently observed control of photoionization of atoms under IR and XUV pulses. By manipulating phases of FPTs we demonstrate an enhancement of molecular dissociation compared to the transform-limited case.

  2. Nonlinear High-Energy Pulse Propagation in Graded-Index Multimode Optical Fibers for Mode-Locked Fiber Lasers

    Science.gov (United States)

    2014-12-23

    is a reasonable approximation, which is also supported by experi- mental measurements [15]. Therefore, we derive a generalized Sellmeier equation to...value of ~L is chosen such that, in the linear case, the relative power transmission is at its mini - mum value. The most notable differences between...spatial profiles Fe(x) = Fe(−x) and Fo(x) = −Fo(−x) being invariant along the y-axis. The symmetries of these two profiles are dictated by the parity

  3. Observation of phase noise reduction in photonically synthesized sub-THz signals using a passively mode-locked laser diode and highly selective optical filtering

    DEFF Research Database (Denmark)

    Criado, A. R.; Acedo, P.; Carpintero, G.

    2012-01-01

    A Continuous Wave (CW) sub-THz photonic synthesis setup based on a single Passively Mode-Locked Laser Diode (PMLLD) acting as a monolithic Optical Frequency Comb Generator (OFCG) and highly selective optical filtering has been implemented to evaluate the phase noise performance of the generated sub...

  4. Retinal polarization-sensitive optical coherence tomography at 1060 nm with 350 kHz A-scan rate using an Fourier domain mode locked laser

    DEFF Research Database (Denmark)

    Torzicky, Teresa; Marschall, Sebastian; Pircher, Michael

    2013-01-01

    We present a novel, high-speed, polarization-sensitive, optical coherence tomography set-up for retinal imaging operating at a central wavelength of 1060 nm which was tested for in vivo imaging in healthy human volunteers. We use the system in combination with a Fourier domain mode locked laser...

  5. Towards low timing phase noise operation in fiber lasers mode locked by graphene oxide and carbon nanotubes at 1.5 µm.

    Science.gov (United States)

    Wu, Kan; Li, Xiaohui; Wang, Yonggang; Wang, Qi Jie; Shum, Perry Ping; Chen, Jianping

    2015-01-12

    We investigate the timing phase noise of fiber lasers mode locked by graphene oxide (GO) and carbon nanotubes (CNTs), respectively, integrated in a linear cavity fiber laser in the reflecting operation. Due to the shorter decay time of the GO and CNTs, weaker slow saturable absorber effects are expected and mode-locked lasers based on these two saturable absorbers exhibit low excess timing phase noise coupled from the laser intensity noise. Compared with a reference laser mode locked by semiconductor saturable absorber mirror (SESAM), GO based laser obtains a timing phase noise reduction of 7 dB at 1 kHz and a timing jitter reduction of 45% experimentally whereas CNTs based laser obtains a timing phase noise reduction of 3 dB and a timing jitter reduction of 29%. This finding suggests that saturable absorbers with short decay time have the potential for achieving mode locking operation with low timing phase noise, which is important for applications including frequency metrology, high-precision optical sampling, clock distribution and optical sensing.

  6. Amplitude characteristics of a solid-state ring laser with active mode locking

    Energy Technology Data Exchange (ETDEWEB)

    Belkina, E.M.; Klochan, E.L.; Lariontsev, E.G.

    1986-09-01

    A system of equations is obtained for the parameters of ultrashort light pulses (USLP) in a solid-state ring laser (SSRL) with periodic loss modulation. Allowance is made for the coupling between counterpropagating USLP due to backscattering in the modulator. The regime of counter-propagating wave frequency capture (CPWFC) is studied. It is shown that the coupling of counterpropagating waves due to backscattering at the modulator ends leads to the suppression of one of the counterpropagating waves during an increase in the detuning of the modulation frequency relative to its optimal value. The influence of rotation on the amplitude characteristics of an SSRL in the CPWFC regime is studied. 9 references.

  7. Trains of electron pulses generation using multi-stage cavities

    International Nuclear Information System (INIS)

    Kamada, Masaki; Mori, Michiya; Sugawara, Kazuyoshi; Yamada, Yoko; Kurihara, Kazuteru; Shirasaka, Haruki; Nishiguchi, Takashi; Ando, Ritoku; Kamada, Keiichi

    2002-01-01

    Automodulation of an intense relativistic electron beam was reexamined experimentally to obtain trains of subnanosecond electron bunches. Sufficient beam modulation with frequency larger than 1 GHz was expected for the trains of subnanosecond bunches. It was obtained when a short pulse electron beam with energy of 550 keV, current of 4 kA, pulse duration of 12 ns and current rise time of 2ns was injected to a series of four coaxial cavities with the length of 75 mm. However, only a poor modulation was observed when a long pulse electron beam of 700 keV, 4 kA, 175 ns with current rise time of 20 ns was injected to the same cavities. Transmission line theory as well PIC code simulation suggested that the round trip time for the electromagnetic wave in the cavity must be longer than the rise time of the beam current to obtain the high level current modulation. Therefore, we studied experimentally how the ratio between the beam current rise time and the length of the cavity affects on the level of current modulation. Single cavity experiments were carried out with the short pulse beam. Single cavity with the length of 75, 150 or 300 mm was utilized. The round trip times for 75 and 150 mm cavities are shorter than the current rise time of 2 ns. The experiments with a 75 or 150 mm cavity resulted in suppression of the modulation amplitude. In the case of a 300 mm cavity, the high level modulation was obtained. The simulation results showed good agreements with the experimental results. We employed a series of cavities with decreasing lengths to improve the current rise time. For the short pulse beam, the high level current 1 GHz modulation was obtained when two 75 mm cavities were set at the downstream side of cavities with lengths of 300 mm and 150 mm. (author)

  8. Steering population transfer of the Na2 molecule by an ultrashort pulse train

    Science.gov (United States)

    Niu, Dong-Hua; Wang, Shuo; Zhan, Wei-Shen; Tao, Hong-Cai; Wang, Si-Qi

    2018-05-01

    We theoretically investigate the complete population transfer among quantum states of the Na2 molecule using ultrashort pulse trains using the time-dependent wave packet method. The population accumulation of the target state can be steered by controlling the laser parameters, such as the variable pulse pairs, the different pulse widths, the time delays and the repetition period between two contiguous pulses; in particular, the pulse pairs and the pulse widths have a great effect on the population transfer. The calculations show that the ultrashort pulse train is a feasible solution, which can steer the population transfer from the initial state to the target state efficiently with lower peak intensities.

  9. High-power parametric amplification of 11.8-fs laser pulses with carrier-envelope phase control

    NARCIS (Netherlands)

    Zinkstok, R.T.; Witte, S.; Hogervorst, W.; Eikema, K.S.E.

    2005-01-01

    Phase-stable parametric chirped-pulse amplification of ultrashort pulses from a carrier-envelope phase-stabilized mode-locked Ti:sapphire oscillator (11.0 fs) to 0.25 mJ/pulse at 1 kHz is demonstrated. Compression with a grating compressor and a LCD shaper yields near-Fourier-limited 11.8-fs pulses

  10. Simultaneous generation of wavelength division multiplexing PON and RoF signals using a hybrid mode-locked laser

    Science.gov (United States)

    Aldaya, Ivan; Campuzano, Gabriel; Castañón, Gerardo

    2015-06-01

    The use of millimeter-wave (mm-wave) frequencies has been proposed to overcome the imminent saturation of the ultra high frequency band, justifying research on radio over fiber (RoF) networks as an inexpensive and green solution to distribute multi-Gbps signals. Coincidently, telecommunication operators are investing a significant effort to deploy their passive optical network (PON) infrastructure closer to the users. In this work, we present a novel cost-efficient architecture based on a hybrid mode locked laser capable to simultaneously generate up-to 5 wavelength division multiplexing PON and RoF channels, being compatible with the 50-GHz ITU frequency grid. We analyze the limits of operation of our proposed architecture considering the high modal relative intensity noise induced by mode partition noise, as well as fiber impairments, such as chromatic dispersion and nonlinearities. The feasibility of generation and transmission of 5×10-Gbps PON and 5×5-Gbps RoF using orthogonal frequency division multiplexing up to 50 km has been demonstrated through realistic numerical simulations.

  11. Calibrated Link Budget of a Silicon Photonics WDM Transceiver with SOA and Semiconductor Mode-Locked Laser.

    Science.gov (United States)

    Moscoso-Mártir, Alvaro; Müller, Juliana; Islamova, Elmira; Merget, Florian; Witzens, Jeremy

    2017-09-20

    Based on the single channel characterization of a Silicon Photonics (SiP) transceiver with Semiconductor Optical Amplifier (SOA) and semiconductor Mode-Locked Laser (MLL), we evaluate the optical power budget of a corresponding Wavelength Division Multiplexed (WDM) link in which penalties associated to multi-channel operation and the management of polarization diversity are introduced. In particular, channel cross-talk as well as Cross Gain Modulation (XGM) and Four Wave Mixing (FWM) inside the SOA are taken into account. Based on these link budget models, the technology is expected to support up to 12 multiplexed channels without channel pre-emphasis or equalization. Forward Error Correction (FEC) does not appear to be required at 14 Gbps if the SOA is maintained at 25 °C and MLL-to-SiP as well as SiP-to-SOA interface losses can be maintained below 3 dB. In semi-cooled operation with an SOA temperature below 55 °C, multi-channel operation is expected to be compatible with standard 802.3bj Reed-Solomon FEC at 14 Gbps provided interface losses are maintained below 4.5 dB. With these interface losses and some improvements to the Transmitter (Tx) and Receiver (Rx) electronics, 25 Gbps multi-channel operation is expected to be compatible with 7% overhead hard decision FEC.

  12. MHD-mode locking by controlled halo-current in the T-10 tokamak

    International Nuclear Information System (INIS)

    Ivanov, N.V.; Chudnovskiy, A.N.; Gvozdkov, Yu.V.; Kakurin, A.M.; Orlovskiy, I.I.; Pavlov, Yu.D.; Piterskiy, V.V.; Safonova, M.B.; Volkov, V.V.

    2003-01-01

    Experiments on a non-disruptive halo-current influence on the m = 2 mode behaviour at the flat-top stage of a tokamak discharge are presented. The halo-current in the Rail Limiter - Plasma - Vacuum Vessel - External Circuit - Rail Limiter loop was used. An EMF source controlled with a pre-programmed signal or with a feedback m = 2 signal was introduced into the external part of the halo-current circuit. The EMF source generated oscillating halo-currents with up to 500 A amplitude in the frequency range 0-20 kHz. In the case of the pre-programmed control signal the switching on of the EMF source resulted in the shift of the m = 2 mode frequency to the frequency of the halo-current oscillations. In particular, the rotation of the m = 2 mode stopped under a pulse of zero-frequency halo-current. In the tokamak discharges when the mode rotation stopped by itself before the switching on of the oscillating halo-current, the mode rotation was restored at the halo-current frequency. In the case of the halo-current feedback control by the m = 2 mode signal, the effect depended on the choice of the phase shift in the feedback loop. Some increase or decrease of the m = 2 mode amplitude as well as some variations of the mode frequency were observed at different values of the phase shift. The halo-current effect on the m = 2 mode behaviour can be attributed to a coupling between the m/n = 2/1 magnetic islands and the halo-current magnetic field. The experiment was simulated on the assumption that the tearing mode is affected by the halo-current magnetic field helical component with the same space structure. The equation for the disturbed poloidal flux in the presence of the external helical surface current was used for the analysis. In the calculations for the T-10 conditions, the mode behaviour under the effect of the halo-current was similar to the experimental observations. (author)

  13. Hybrid Pulsed Nd:YAG Laser

    Science.gov (United States)

    Miller, Sawyer; Trujillo, Skyler; Fort Lewis College Laser Group Team

    This work concerns the novel design of an inexpensive pulsed Nd:YAG laser, consisting of a hybrid Kerr Mode Lock (KLM) and Q-switch pulse. The two pulse generation systems work independently, non simultaneously of each other, thus generating the ability for the user to easily switch between ultra-short pulse widths or large energy density pulses. Traditionally, SF57 glass has been used as the Kerr medium. In this work, novel Kerr mode-locking mediums are being investigated including: tellurite compound glass (TeO2), carbon disulfide (CS2), and chalcogenide glass. These materials have a nonlinear index of refraction orders of magnitude,(n2), larger than SF57 glass. The Q-switched pulse will utilize a Pockels cell. As the two pulse generation systems cannot be operated simultaneously, the Pockels cell and Kerr medium are attached to kinematic mounts, allowing for quick interchange between systems. Pulse widths and repetition rates will vary between the two systems. A goal of 100 picosecond pulse widths are desired for the mode-locked system. A goal of 10 nanosecond pulse widths are desired for the Q-switch system, with a desired repetition rate of 50 Hz. As designed, the laser will be useful in imaging applications.

  14. Soliton rains in a graphene-oxide passively mode-locked ytterbium-doped fiber laser with all-normal dispersion

    International Nuclear Information System (INIS)

    Huang, S S; Yan, P G; Zhang, G L; Zhao, J Q; Li, H Q; Lin, R Y; Wang, Y G

    2014-01-01

    We experimentally investigated soliton rains in an ytterbium-doped fiber (YDF) laser with a net normal dispersion cavity using a graphene-oxide (GO) saturable absorber (SA). The 195 m-long-cavity, the fiber birefringence filter and the inserted 2.5 nm narrow bandwidth filter play important roles in the formation of the soliton rains. The soliton rain states can be changed by the effective gain bandwidth of the laser. The experimental results can be conducive to an understanding of dissipative soliton features and mode-locking dynamics in all-normal dispersion fiber lasers with GOSAs. To the best of our knowledge, this is the first demonstration of soliton rains in a GOSA passively mode-locked YDF laser with a net normal dispersion cavity. (letter)

  15. Analysis of soft-aperture Kerr-lens mode-locking in Ti:sapphire laser cavities using nonlinear ABCD-matrix

    International Nuclear Information System (INIS)

    Lee, Yong Woo; Cha, Yong Ho; Rhee, Yong Joo; Yoo, Byung Duk; Lee, Byoung Chul

    2004-01-01

    We have numerically analyzed the effect of soft-aperture Kerr-lens mode locking in Ti:sapphire laser cavities. Because the Kerr-lens effect depends on the intracavitiy power, we used nonlinear ABCD-matrix to calculated the power-dependent beam mode inside a cavity. In soft-aperture Kerr-lens mode locking, the Kerr-lens effect is strongly dependent on the position of the crystal, the separation of two curved mirrors, and the cavity length. Figure 1 is the schematic of the Ti:sapphire laser cavity used in our calculation. It consists of a Ti:sapphire crystal (Kerr medium), two curved mirrors, and flat mirrors. Lc is the Ti:sapphire crystal length, D1 the length between M1 and M3, D2 the length between M2 and M4, L1 the length between the crystal and M1, and L2 the length between crystal and M2

  16. Uniform spacing interrogation of a Fourier domain mode-locked fiber Bragg grating sensor system using a polarization-maintaining fiber Sagnac interferometer

    OpenAIRE

    Lee, Hwi Don; Jung, Eun Joo; Jeong, Myung Yung; Chen, Zhongping; Kim, Chang-Seok

    2013-01-01

    A novel linearized interrogation method is presented for a Fourier domain mode-locked (FDML) fiber Bragg grating (FBG) sensor system. In a high speed regime over several tens of kHz modulations, a sinusoidal wave is available to scan the center wavelength of an FDML wavelength-swept laser, instead of a conventional triangular wave. However, sinusoidal wave modulation suffers from an exaggerated non-uniform wavelength-spacing response in demodulating the time-encoded parameter to the absolute ...

  17. Medium-gain erbium doped fiber amplifier ring laser passively mode-locked by graphite nano-powder adhered thin PVA film

    Science.gov (United States)

    Lin, Yung-Hsiang; Lin, Gong-Ru

    2012-06-01

    A direct brushing process of graphite nano-powder adhered on the single-mode fiber end-face with the use of an ultrathin PVA film is demonstrated, such a graphite nano-powder adhered ultra-thin PVA film is introduced to passively mode-lock a medium-gain Erbium-doped fiber laser (EDFL). The structural property of the graphite nano-powder is investigated by Raman spectroscopy. Numerous structural defects induced when abrading the graphite into nano-powder are found to broaden the 2D band Raman scattered signal and attenuate its peak intensity. The graphite nano-powders exhibit the featureless transmittance to show the potential as being a broadband tuning saturable absorber. In addition, the modulation depth of 0.43 is comparable with the graphene saturable absorber. The central wavelength of the passively mode-locked medium-gain EDFL is at 1561.2 nm with the full width at half maximum (FHWM) of 1.62 nm, and the pulsewidth is 1.58 ps. Under the limited intra-cavity power of 18 dBm, a nearly transform-limited passively mode-locking EDFL with TBP of 0.32 is generated.

  18. An experimental comparison of triggered and random pulse train uncertainties

    International Nuclear Information System (INIS)

    Henzlova, Daniela; Menlove, Howard O.; Swinhoe, Martyn T.

    2010-01-01

    response) have used only one of the two analysis methods for the nuclear material assay. The aim of this study is to provide a systematic comparison of the precision of the measured S, D, T rates and 240 Pu effective mass obtained using the above mentioned pulse train sampling techniques. In order to perform this task, a LANL developed list mode based data acquisition system is used, where the entire pulse train is recorded and subsequently analyzed. The list mode acquisition brings an essential advantage for this type of comparison, since the very same pulse train can be analyzed using signal-triggered as well as randomly triggered counting gates. The aim of this study is not only to compare the precision of signal-triggered versus random triggered sampling techniques, but also to investigate the influence of fast accidental sampling on the precision of signal-triggered results. In addition the different random sampling techniques used in safeguards are investigated. For this purpose we implement two types of random sampling - non-overlapping gates (Feynrnan approach) and periodic overlapping gates (fast accidentals). In the following sections the equations utilized in the pulse train analysis are described, experimental setup and measurement techniques are discussed and finally the results are summarized and discussed.

  19. Selective generation of two pulse modes in a single all normal dispersion fiber laser oscillator and analysis of their optical characteristics

    Science.gov (United States)

    Kim, S.; Choi, M.; Song, J. Y.; Lee, J. H.; Kim, Y.

    2017-02-01

    Fiber ultrafast pulses such as mode-locked and noise-like pulses have useful optical characteristics for high precision metrology applications. In this study, we develop an ytterbium doped fiber laser with all normal dispersion which can selectively generate two pulse modes, mode-locked and noise-like pulses, by a turn-key system including polarization control and selective detection parts. The spectral and temporal characteristics of two pulses generated from the single oscillator are analyzed and compared with each other through optical spectrum, RF spectrum and autocorrelation. Furthermore, spectral coherence characteristics are verified through interference signals generated by balanced and unbalanced arm interferometers.

  20. Tunable CO2 laser system with subnanosecond-pulse-train output

    Science.gov (United States)

    Kimura, W. D.

    2017-02-01

    A CO2 laser system has been demonstrated that generates a train of subnanosecond pulses tunable over the P and R branches of the CO2 laser spectrum at 9-11 μm. It utilizes optical free induction decay to generate a single 100-ps laser pulse from a tunable transverse-excited-atmospheric CO2 laser. This laser pulse is injection-seeded into a high-pressure CO2 oscillator whose output consists of a train of amplified 100-ps pulses with maximum pulse energy of 30 mJ, corresponding to a peak power of 300 MW. The 100-ps, tunable, infrared laser pulses are needed for a new technique to remotely detect atmospheric gaseous molecules, which relies on the train of CO2 laser pulses selectively exciting the target molecules whose presence is then revealed using a separate terahertz probe beam.

  1. Pulse train amplification and regeneration based on semiconductor quantum dots waveguide

    DEFF Research Database (Denmark)

    Chen, Yaohui; Öhman, Filip; Mørk, Jesper

    2008-01-01

    We numerical analyze pulse train amplification up to 200 Gbit/s in quantum dot amplifiers and present regeneration properties with saturable absorber based on semiconductor quantum dot waveguides.......We numerical analyze pulse train amplification up to 200 Gbit/s in quantum dot amplifiers and present regeneration properties with saturable absorber based on semiconductor quantum dot waveguides....

  2. Observation of subfemtosecond fluctuations of the pulse separation in a soliton molecule.

    Science.gov (United States)

    Shi, Haosen; Song, Youjian; Wang, Chingyue; Zhao, Luming; Hu, Minglie

    2018-04-01

    In this work, we study the timing instability of a scalar twin-pulse soliton molecule generated by a passively mode-locked Er-fiber laser. Subfemtosecond precision relative timing jitter characterization between the two solitons composing the molecule is enabled by the balanced optical cross-correlation (BOC) method. Jitter spectral density reveals a short-term (on the microsecond to millisecond timescale) random fluctuation of the pulse separation even in the robust stationary soliton molecules. The root-mean-square (rms) timing jitter is on the order of femtoseconds depending on the pulse separation and the mode-locking regime. The lowest rms timing jitter is 0.83 fs, which is observed in the dispersion managed mode-locking regime. Moreover, the BOC method has proved to be capable of resolving the soliton interaction dynamics in various vibrating soliton molecules.

  3. Design and Characteristic Analysis of Multicarrier Chaotic Phase Coded Radar Pulse Train Signal

    Directory of Open Access Journals (Sweden)

    Qiongdan Huang

    2014-01-01

    Full Text Available By introducing phase code into multicarrier orthogonal frequency division multiplex signal, the multicarrier phase coded (MCPC radar signal possesses a good spectrum utilization rate and can achieve a good combination of narrowband and wideband processing. Radar pulse train signal not only reserves the high range resolution of monopulse signal, but also has the same velocity resolution performance as continuous wave signal does. In this study, we use the chaotic biphase code generated by Chebyshev mapping to conduct a phase modulation on MCPC pulse train so as to design two different types of multicarrier chaotic phase coded pulse train signal. The ambiguity functions of the two pulse train signals are compared with that of P4 code MCPC pulse train. In addition, we analyze the influences of subcarrier number, phase-modulated bit number, and period number on the pulse train’s autocorrelation performance. The low probability of intercept (LPI performance of the two signals is also discussed. Simulation results show that the designed pulse train signals have a thumbtack ambiguity function, a periodic autocorrelation side lobe lower than P4 code MCPC pulse train, and excellent LPI performance, as well as the feature of waveform diversity.

  4. BRIEF COMMUNICATIONS: Limiting parameters of ultrashort pulses from a lanthanum beryllate laser

    Science.gov (United States)

    Demchuk, M. I.; Mikhaĭlov, V. P.; Gilev, A. K.; Shkadarevich, A. P.; Stavrov, A. A.; Kovalev, D. V.

    1985-06-01

    An investigation was made of passive mode locking using lanthanum beryllate as the active medium. Various passive switches were used to study the influence of their nonlinear parameters on the characteristics of ultrashort pulses. A minimal ultrashort pulse duration of ~ 4 psec was obtained.

  5. Generation of pulse trains with high-repetition-rate in anomalous dispersion decreasing fibers

    Science.gov (United States)

    Korobko, Dmitry A.; Okhotnikov, Oleg G.; Sysoliatin, Alex A.; Zolotovskii, Igor O.

    2014-03-01

    Optical pulse generation and compression have been numerically studied in anomalous dispersion decreasing fibers (DDF). We show that evolution of modulation instability observed with chirped wave packets in tapered fibers produces the mechanism for generation of ultra-short pulses with high repetition rates. The role of modulation instability and Raman self-scattering has been also discussed. The simulations show that pulse chirping enhances self-Raman scattering at early stages of pulse propagation and improves compression of the generated pulses. It is also shown that the presence of amplitude and frequency modulation of the seed wave provide essential impact on the pulse train formation. The new method for increasing the pulse train repetition rate through frequency modulation of the seed wave has been proposed.

  6. Sintering of solution-based nano-particles by a UV laser pulse train

    Science.gov (United States)

    Zhang, Jie; Li, Ming; Morimoto, Kiyoshi

    2011-03-01

    Sintering of palladium (Pd) and silicon (Si) nano-particles (NPs) by a 266nm laser pulse train on ink-printed films was investigated. Organic Pd-ink, and organic Si-ink were used as precursors. A high repetition rate DPSS laser (up to 300 kHz, 25ns, 266nm, Coherent AVIA series), which produces a ns pulse train with 3.3 μs -33.3 μs interval of pulse-topulse, was used as the heating source. Highly electrically conductive Pd (Resistivity=~150μΩ.cm) thin film on PET substrate and semi-conductive Si (Resistivity=~23kΩ.cm) thin film on glass substrate were successfully obtained with this laser pulse train sintering process. The sintered films were characterized by AFM, SEM, TEM and Raman spectroscopy, respectively. The pulse train heating process was also numerically simulated.

  7. Buffered Fourier domain mode locking: Unidirectional swept laser sources for optical coherence tomography imaging at 370,000 lines/s.

    Science.gov (United States)

    Huber, Robert; Adler, Desmond C; Fujimoto, James G

    2006-10-15

    We describe buffered Fourier domain mode locking (FDML), a technique for tailoring the output and multiplying the sweep rate of FDML lasers. Buffered FDML can be used to create unidirectional wavelength sweeps from the normal bidirectional sweeps in an FDML laser without sacrificing sweep rate. We also investigate the role of the laser source in dynamic range versus sensitivity performance in optical coherence tomography (OCT) imaging. Unidirectional sweep rates of 370 kHz over a 100 nm range at a center wavelength of 1300 nm are achieved. High-speed, swept-source OCT is demonstrated at record speeds of up to 370,000 axial scans per second.

  8. Secondary wavelength stabilization of unbalanced Michelson interferometers for the generation of low-jitter pulse trains.

    Science.gov (United States)

    Shalloo, R J; Corner, L

    2016-09-01

    We present a double unbalanced Michelson interferometer producing up to four output pulses from a single input pulse. The interferometer is stabilized with the Hänsch-Couillaud method using an auxiliary low power continuous wave laser injected into the interferometer, allowing the stabilization of the temporal jitter of the output pulses to 0.02 fs. Such stabilized pulse trains would be suitable for driving multi-pulse laser wakefield accelerators, and the technique could be extended to include amplification in the arms of the interferometer.

  9. Phase Noise Comparision of Short Pulse Laser Systems

    Energy Technology Data Exchange (ETDEWEB)

    S. Zhang; S. V. Benson; J. Hansknecht; D. Hardy; G. Neil; Michelle D. Shinn

    2006-12-01

    This paper describes the phase noise measurement on several different mode-locked laser systems that have completely different gain media and configurations including a multi-kW free-electron laser. We will focus on the state of the art short pulse lasers, especially the drive lasers for photocathode injectors. A comparison between the phase noise of the drive laser pulses, electron bunches and FEL pulses will also be presented.

  10. Hybrid adiabatic-rectangular pulse train for effective saturation of magnetization within the whole heart at 3 T.

    Science.gov (United States)

    Kim, Daniel; Oesingmann, Niels; McGorty, Kellyanne

    2009-12-01

    Uniform T(1)-weighting is a major challenge for first-pass cardiac perfusion MRI at 3 T. Previously proposed adiabatic amplitude of radiofrequency field (B(1))-insensitive rotation (BIR-4) pulse and standard and tailored pulse trains of three nonselective pulses have been important developments but each pulse has limitations at 3 T. As an extension of the tailored pulse train, we developed a hybrid pulse train by synergistically combining two nonselective rectangular radiofrequency pulses and an adiabatic half-passage pulse, in order to achieve effective saturation of magnetization within the heart, while remaining within clinically acceptable specific absorption rate limits. The standard pulse train, tailored pulse train, hybrid pulse train, and BIR-4 pulse train were evaluated through numerical, phantom, and in vivo experiments. Among the four saturation pulses, only the hybrid pulse train yielded residual magnetization magnetization in the heart while remaining within clinically acceptable specific absorption rate limits for multislice first-pass cardiac perfusion MRI at 3 T. (c) 2009 Wiley-Liss, Inc.

  11. Hybrid Adiabatic-Rectangular Pulse Train for Effective Saturation of Magnetization within the Whole Heart at 3T

    Science.gov (United States)

    Kim, Daniel; Oesingmann, Niels; McGorty, KellyAnne

    2009-01-01

    Uniform T1-weighting is a major challenge for first-pass cardiac perfusion MRI at 3T. Previously proposed adiabatic B1-insensitive rotation (BIR-4) pulse and standard and tailored pulse trains of three non-selective pulses have been important developments but each pulse has limitations at 3T. As an extension of the tailored pulse train, we developed a hybrid pulse train by synergistically combining two non-selective rectangular RF pulses and an adiabatic half-passage pulse, in order to achieve effective saturation of magnetization within the heart, while remaining within clinically acceptable specific absorption rate (SAR) limits. The standard pulse train, tailored pulse train, hybrid pulse train, and BIR-4 pulse train were evaluated through numerical, phantom, and in vivo experiments. Among the four saturation pulses, only the hybrid pulse train yielded residual magnetization < 2% of equilibrium magnetization in the heart, while remaining within clinically acceptable SAR limits for multi-slice first-pass cardiac perfusion MRI at 3T. PMID:19785021

  12. A new coding concept for fast ultrasound imaging using pulse trains

    DEFF Research Database (Denmark)

    Misaridis, T.; Jensen, Jørgen Arendt

    2002-01-01

    . In this paper, an alternative combined time-space coding approach is undertaken. In the new method all transducer elements are excited with short pulses and the high time-bandwidth (TB) product waveforms are generated acoustically. Each element transmits a short pulse spherical wave with a constant transmit...... delay from element to element, long enough to assure no pulse overlapping for all depths in the image. Frequency shift keying is used for "per element" coding. The received signals from a point scatterer are staggered pulse trains which are beamformed for all beam directions and further processed...... with a bank of matched filters (one for each beam direction). Filtering compresses the pulse train to a single pulse at the scatterer position with a number of spike axial sidelobes. Cancellation of the ambiguity spikes is done by applying additional phase modulation from one emission to the next and summing...

  13. Digital parallel-to-series pulse-train converter

    Science.gov (United States)

    Hussey, J.

    1971-01-01

    Circuit converts number represented as two level signal on n-bit lines to series of pulses on one of two lines, depending on sign of number. Converter accepts parallel binary input data and produces number of output pulses equal to number represented by input data.

  14. Autler-Townes doublet and electromagnetically induced transparency resonance probed by an ultrashort pulse train

    International Nuclear Information System (INIS)

    Soares, A A; De Araujo, Luis E E

    2010-01-01

    We study theoretically the interaction between an ultrashort pulse train and a three-level atom driven by a cw laser. We show that the pulse train can be employed to observe spectra of Autler-Townes doublet and electromagnetically induced transparency resonance that are time and frequency resolved. The observation of subnatural linewidth features associated with the electromagnetically induced transparency resonance is described. The temporal evolution of electromagnetically induced transparency of the pulse train is shown to exhibit new and different features compared to that of the related phenomenon of coherent population trapping. By matching the tooth separation of the frequency comb associated with the pulse train to that of the Autler-Townes doublet, quantum beats between the doublet components can be induced. We show that coherent accumulation of excitation plays a major role in the two studied phenomena.

  15. Optimization of pulse train presaturation for CEST imaging in clinical scanners.

    Science.gov (United States)

    Schmitt, Benjamin; Zaiss, Moritz; Zhou, Jinyuan; Bachert, Peter

    2011-06-01

    Chemical exchange saturation transfer (CEST) imaging depends on the performance of radiofrequency saturation during the experiment. Scanner specifications, in particular limited pulse width and duty-cycle, and specific absorption rate guidelines restrict the full exploitation of CEST effects in clinical MR systems. The purpose of this study was to optimize techniques for effective pulse train presaturation for CEST imaging in a whole-body MR scanner. Theoretical analysis and simulations of the spectral properties of radiofrequency pulse trains demonstrated the significance of pulse width τ(P) and interpulse delay τ(D) for effective and selective labeling of a chemically exchanging proton pool. CEST experiments with model solutions, e.g., creatine dissolved in water, showed best performance of pulse trains with τ(P) = τ(D) = 100 msec, regarding minimum direct water saturation in z-spectra and distinct magnetization transfer ratio asymmetry that can be determined quantitatively. Saturation efficiency of trains of Gaussian-shaped radiofrequency pulses using this timing was evaluated in MR imagers with field strengths of 1.5, 3, and 7 T. The proposed saturation pulse train does not require hardware modifications, offers low specific absorption rate, and can be used in a standard clinical setup. Copyright © 2011 Wiley-Liss, Inc.

  16. Interaction Of CO2 Laser Nanosecond Pulse Train With The Metallic Targets In Optical Breakdown Regime

    Science.gov (United States)

    Apollonov, V. V.; Firsov, K. N.; Konov, V. I.; Nikitin, P. I.; Prokhorov, A. M.; Silenok, A. S.; Sorochenko, V. R.

    1986-11-01

    In the present paper the electric field and currents in the air-breakdown plasma, produced by the train of nanosecond pulses of TEA-002 - regenerative amplifier near the un-charged targets are studied. The breakdown thresholds and the efficiency of plasma-target heat transmission are also measured. The results of numerical calculations made for increasing of the pulse train contrast with respect to the background in a regenerative amplifier are advanced.

  17. Theoretical Study of an Actively Mode-Locked Fiber Laser Stabilized by an Intracavity Fabry-Perot Etalon: Linear Regime

    Science.gov (United States)

    2007-07-01

    competition without a significant ncrease in the pulse duration. . MATHEMATICAL MODEL FOR THE ASER ur mathematical model of the laser is similar to...to he case 1=0. The increase in the parameter P̂ yields an ncrease in the pulse duration by a factor of approxi- ately 10. It is possible to...etalon and it increases as the finesse of the etalon ncreases . Therefore, in a laser with an etalon, the total ispersion is determined by the parameter D̂

  18. Concentrating laser pulses in space and time

    Science.gov (United States)

    McAulay, Alastair D.

    2006-08-01

    Projecting high peak power laser pulses to a specific location in space and time can significantly improve laser weapons, secure optical communications, and remote spectroscopy. Current laser systems send a pulsed beam from laser to target causing collateral damage to objects in the path for a laser weapon system, opportunities for compromising security in communications, and averaging of measurements along the path for spectroscopy. We analyze and simulate a system that beamforms M mode-locked lasers, each having N modes, to achieve a peak power at a target in space and time that is NM times greater than that for M non-mode-locked non-beamformed lasers. In low atmospheric turbulence, a peak power of 10kW can be projected to a point in space and time by a 10 × 10 array of 2W laser diodes, each having 50 modes. Effects of atmospheric turbulence are discussed and were investigated in our previous papers.

  19. Effect of narrow spectral filter position on the characteristics of active similariton mode-locked femtosecond fiber laser.

    Science.gov (United States)

    Kotb, Hussein; Abdelalim, Mohamed A; Anis, Hanan

    2015-11-16

    A significant change in active similariton characteristics, both numerically and experimentally, is observed as a function of the location of the lumped spectral filter. The closer the spectral filter is to the input of the Yb(3+)-doped fiber, the shorter the de-chirped pulse width. The peak power of the de-chirped pulse has its maximum value at a certain location of the spectral filter. Four different positions of the spectral filter inside the laser cavity have been theoretically studied and two of them have been verified experimentally.

  20. Phase-sensitive optical coherence tomography at up to 370,000 lines per second using buffered Fourier domain mode-locked lasers.

    Science.gov (United States)

    Adler, Desmond C; Huber, Robert; Fujimoto, James G

    2007-03-15

    Buffered Fourier domain mode-locked (FDML) lasers are demonstrated for dynamic phase-sensitive optical coherence tomography (OCT) and 3D OCT phase microscopy. Systems are operated at sweep speeds of 42, 117, and 370 kHz, and displacement sensitivities of 39, 52, and 102 pm are achieved, respectively. Sensitivities are comparable to spectrometer-based OCT phase microscopy systems, but much faster acquisition speeds are possible. An additional factor of sqrt 2 improvement in noise performance is observed for differential phase measurements, which is important for Doppler OCT. Dynamic measurements of piezoelectric transducer motion and static 3D OCT phase microscopy are demonstrated. Buffered FDML lasers provide excellent displacement sensitivities at extremely high sweep speeds.

  1. Fourier domain mode locking at 1050 nm for ultra-high-speed optical coherence tomography of the human retina at 236,000 axial scans per second.

    Science.gov (United States)

    Huber, R; Adler, D C; Srinivasan, V J; Fujimoto, J G

    2007-07-15

    A Fourier domain mode-locked (FDML) laser at 1050 nm for ultra-high-speed optical coherence tomography (OCT) imaging of the human retina is demonstrated. Achievable performance, physical limitations, design rules, and scaling principles for FDML operation and component choice in this wavelength range are discussed. The fiber-based FDML laser operates at a sweep rate of 236 kHz over a 63 nm tuning range, with 7 mW average output power. Ultra-high-speed retinal imaging is demonstrated at 236,000 axial scans per second. This represents a speed improvement of approximately10x over typical high-speed OCT systems, paving the way for densely sampled volumetric data sets and new imaging protocols.

  2. Dynamic and static strain fiber Bragg grating sensor interrogation with a 1.3 µm Fourier domain mode-locked wavelength-swept laser

    International Nuclear Information System (INIS)

    Lee, Byoung Chang; Jeon, Min Yong; Jung, Eun-Joo; Kim, Chang-Seok

    2010-01-01

    We demonstrate dynamic and static strain fiber Bragg grating (FBG) sensor array interrogation using a 1.3 µm Fourier-domain mode-locked (FDML) wavelength-swept laser. The FDML wavelength-swept laser provides a high speed scanning rate and wide scanning bandwidth. Using the FDML wavelength swept laser, we measure the performances of static strain sensor interrogation for both time and spectral domains. The slope coefficients for the measured relative wavelength difference and relative time delay from the static strain are 0.8 pm/µstrain and 0.086 ns/µstrain, respectively. We demonstrate the dynamic response of the FBG sensor array with a 100 Hz modulating strain based on the FDML wavelength-swept laser at a 40.6 kHz scanning rate. The FBG sensor interrogation system using the FDML wavelength-swept laser can be realized for high-speed and high-sensitivity monitoring systems

  3. Uniform spacing interrogation of a Fourier domain mode-locked fiber Bragg grating sensor system using a polarization-maintaining fiber Sagnac interferometer

    International Nuclear Information System (INIS)

    Lee, Hwi Don; Jeong, Myung Yung; Chen, Zhongping; Kim, Chang-Seok; Jung, Eun Joo

    2013-01-01

    A novel linearized interrogation method is presented for a Fourier domain mode-locked (FDML) fiber Bragg grating (FBG) sensor system. In a high speed regime over several tens of kHz modulations, a sinusoidal wave is available to scan the center wavelength of an FDML wavelength-swept laser, instead of a conventional triangular wave. However, sinusoidal wave modulation suffers from an exaggerated non-uniform wavelength-spacing response in demodulating the time-encoded parameter to the absolute wavelength. In this work, the calibration signal from a polarization-maintaining fiber Sagnac interferometer shares the FDML wavelength-swept laser for FBG sensors to convert the time-encoded FBG signal to the wavelength-encoded uniform-spacing signal. (paper)

  4. Uniform spacing interrogation of a Fourier domain mode-locked fiber Bragg grating sensor system using a polarization-maintaining fiber Sagnac interferometer

    Science.gov (United States)

    Lee, Hwi Don; Jung, Eun Joo; Jeong, Myung Yung; Chen, Zhongping; Kim, Chang-Seok

    2013-06-01

    A novel linearized interrogation method is presented for a Fourier domain mode-locked (FDML) fiber Bragg grating (FBG) sensor system. In a high speed regime over several tens of kHz modulations, a sinusoidal wave is available to scan the center wavelength of an FDML wavelength-swept laser, instead of a conventional triangular wave. However, sinusoidal wave modulation suffers from an exaggerated non-uniform wavelength-spacing response in demodulating the time-encoded parameter to the absolute wavelength. In this work, the calibration signal from a polarization-maintaining fiber Sagnac interferometer shares the FDML wavelength-swept laser for FBG sensors to convert the time-encoded FBG signal to the wavelength-encoded uniform-spacing signal.

  5. Optical frequency comb generator based on a monolithically integrated passive mode-locked ring laser with a Mach-Zehnder interferometer.

    Science.gov (United States)

    Corral, V; Guzmán, R; Gordón, C; Leijtens, X J M; Carpintero, G

    2016-05-01

    We report the demonstration of an optical-frequency comb generator based on a monolithically integrated ring laser fabricated in a multiproject wafer run in an active/passive integration process in a generic foundry using standardized building blocks. The device is based on a passive mode-locked ring laser architecture, which includes a Mach-Zehnder interferometer to flatten the spectral shape of the comb output. This structure allows monolithic integration with other optical components, such as optical filters for wavelength selection, or dual wavelength lasers for their stabilization. The results show a -10  dB span of the optical comb of 8.7 nm (1.08 THz), with comb spacing of 10.16 GHz. We also obtain a flatness of 44 lines within a 1.8 dB power variation.

  6. High-resolution retinal swept source optical coherence tomography with an ultra-wideband Fourier-domain mode-locked laser at MHz A-scan rates.

    Science.gov (United States)

    Kolb, Jan Philip; Pfeiffer, Tom; Eibl, Matthias; Hakert, Hubertus; Huber, Robert

    2018-01-01

    We present a new 1060 nm Fourier domain mode locked laser (FDML laser) with a record 143 nm sweep bandwidth at 2∙ 417 kHz  =  834 kHz and 120 nm at 1.67 MHz, respectively. We show that not only the bandwidth alone, but also the shape of the spectrum is critical for the resulting axial resolution, because of the specific wavelength-dependent absorption of the vitreous. The theoretical limit of our setup lies at 5.9 µm axial resolution. In vivo MHz-OCT imaging of human retina is performed and the image quality is compared to the previous results acquired with 70 nm sweep range, as well as to existing spectral domain OCT data with 2.1 µm axial resolution from literature. We identify benefits of the higher resolution, for example the improved visualization of small blood vessels in the retina besides several others.

  7. Direct generation of 2  W average-power and 232  nJ picosecond pulses from an ultra-simple Yb-doped double-clad fiber laser.

    Science.gov (United States)

    Huang, Yizhong; Luo, Zhengqian; Xiong, Fengfu; Li, Yingyue; Zhong, Min; Cai, Zhiping; Xu, Huiying; Fu, Hongyan

    2015-03-15

    We report the generation of 2.06 W average-power and 232 nJ picosecond mode-locked pulses directly from an ultra-simple Yb-doped fiber laser. A section of Yb-doped double-clad fiber pumped by a 976 nm laser diode provides the large gain, and the linear cavity is simply formed by a 1064 nm highly reflective fiber Bragg grating and a fiber loop mirror (FLM) using a 5/95 optical coupler. The asymmetric FLM not only acts as the output mirror for providing ∼20% optical feedback, but also equivalently behaves as a nonlinear optical loop mirror (NOLM) to initiate the mode-locking operation in this cavity. Stable mode-locking is therefore achieved over a pump power of 3.76 W. The mode-locked pulses show the dissipative soliton resonance (DSR), which has the pulse duration of 695 ps to ∼1  ns, and the almost unchanged peak power of ∼200  W as increasing the pump power. In particular, this laser can emit 232 nJ high-energy DSR pulses with an average output power of >2  W. This is, to the best of our knowledge, the first demonstration of such an ultra-simple, mode-locked fiber laser that enables watt-level, high energy, picosecond DSR pulses.

  8. Burst train generator of high energy femtosecond laser pulses for driving heat accumulation effect during micromachining.

    Science.gov (United States)

    Rezaei, Saeid; Li, Jianzhao; Herman, Peter R

    2015-05-01

    A new method for generating high-repetition-rate (12.7-38.2 MHz) burst trains of femtosecond laser pulses has been demonstrated for the purpose of tailoring ultrashort laser interactions in material processing that can harness the heat accumulation effect among pulses separated by a short interval (i.e., 26 ns). Computer-controlled time delays were applied to synchronously trigger the high frequency switching of a high voltage Pockels cell to specify distinctive values of polarization rotation for each round-trip of a laser pulse cycling within a passive resonator. Polarization dependent output coupling facilitated the flexible shaping of the burst envelope profile to provide burst trains of up to ∼1  mJ of burst energy divided over a selectable number (1 to 25) of pulses. Individual pulses of variable energy up to 150 μJ and with pulse duration tunable over 70 fs to 2 ps, were applied in burst trains to generate deep and high aspect ratio holes that could not form with low-repetition-rate laser pulses.

  9. Comparative study on preliminary breakdown pulse trains observed in Johor, Malaysia and Florida, USA

    Science.gov (United States)

    Baharudin, Z. A.; Ahmad, Noor Azlinda; Fernando, M.; Cooray, V.; Mäkelä, J. S.

    2012-11-01

    In this paper, the preliminary breakdown (PB) pulse train preceding the negative first return stroke (RS) is recorded using a broad band antenna system. These analyses were carried out in Johor Bahru, Malaysia and Florida, United States. This is a novel initiative at examining and identifying the characteristics of the PB pulse trains in the negative cloud-to-ground flashes observed in Malaysia. The arithmetic mean of the total pulse train duration is 12.3 ms and the weighted arithmetic mean of the pulse durations and interpulse intervals are 11 μs and 152 μs, respectively. The arithmetic mean ratio between the maximum peak amplitude of the PB pulse and the peak RS electric field was 27.8%, and the corresponding value in Florida was 29.4%. The arithmetic mean of the time duration between the most active part of the pulse train, and the RS was 57.6 ms in Malaysia and 22 ms in Florida. A qualitative comparison of our results with those obtained earlier in Sri Lanka, Sweden and Finland supports the hypothesis that the PBP/RS ratio is higher in the northern regions compared to the tropical regions.

  10. Forward Masking in Cochlear Implant Users: Electrophysiological and Psychophysical Data Using Pulse Train Maskers.

    Science.gov (United States)

    Adel, Youssef; Hilkhuysen, Gaston; Noreña, Arnaud; Cazals, Yves; Roman, Stéphane; Macherey, Olivier

    2017-06-01

    Electrical stimulation of auditory nerve fibers using cochlear implants (CI) shows psychophysical forward masking (pFM) up to several hundreds of milliseconds. By contrast, recovery of electrically evoked compound action potentials (eCAPs) from forward masking (eFM) was shown to be more rapid, with time constants no greater than a few milliseconds. These discrepancies suggested two main contributors to pFM: a rapid-recovery process due to refractory properties of the auditory nerve and a slow-recovery process arising from more central structures. In the present study, we investigate whether the use of different maskers between eCAP and psychophysical measures, specifically single-pulse versus pulse train maskers, may have been a source of confound.In experiment 1, we measured eFM using the following: a single-pulse masker, a 300-ms low-rate pulse train masker (LTM, 250 pps), and a 300-ms high-rate pulse train masker (HTM, 5000 pps). The maskers were presented either at same physical current (Φ) or at same perceptual (Ψ) level corresponding to comfortable loudness. Responses to a single-pulse probe were measured for masker-probe intervals ranging from 1 to 512 ms. Recovery from masking was much slower for pulse trains than for the single-pulse masker. When presented at Φ level, HTM produced more and longer-lasting masking than LTM. However, results were inconsistent when LTM and HTM were compared at Ψ level. In experiment 2, masked detection thresholds of single-pulse probes were measured using the same pulse train masker conditions. In line with our eFM findings, masked thresholds for HTM were higher than those for LTM at Φ level. However, the opposite result was found when the pulse trains were presented at Ψ level.Our results confirm the presence of slow-recovery phenomena at the level of the auditory nerve in CI users, as previously shown in animal studies. Inconsistencies between eFM and pFM results, despite using the same masking conditions, further

  11. Modeling a Conventional Electroporation Pulse Train: Decreased Pore Number, Cumulative Calcium Transport and an Example of Electrosensitization.

    Science.gov (United States)

    Son, Reuben S; Gowrishankar, Thiruvallur R; Smith, Kyle C; Weaver, James C

    2016-03-01

    Pulse trains are widely used in electroporation (EP) for both general biomedical research and clinical applications such as nonthermal tumor ablation. Here we use a computational method based on a meshed transport network to investigate a cell system model's response to a train of identical, evenly spaced electric field pulses. We obtain an unexpected result: the number of membrane pores decreases during the application of twenty 1.0 kV/cm, 100 μs pulses, delivered at 1 Hz. This pulse train initially creates 13,000 membrane pores, but pore number decreases by a factor of 15 to about 830 pores throughout subsequent pulses. We conclude that pore number can greatly diminish during a train of identical pulses, with direct consequences for the transport of solutes across an electroporated membrane. Although application of additional pulses is generally intended to increase the effects of EP, we show that these pulses do not significantly enhance calcium delivery into the cell. Instead, calcium delivery can be significantly increased by varying inter-pulse intervals. We show that inserting a 300-s interruption midway in a widely used eight-pulse train (a protocol for electrosensitization) yields a ∼ twofold delivery increase. Overall, our modeling shows support for electrosensitization, in which multiple pulse protocols that maximize pore number over time can yield significant increase of transport of calcium compared to standard pulse trains.

  12. Ultrafast fiber lasers based on self-similar pulse evolution: a review of current progress.

    Science.gov (United States)

    Chong, Andy; Wright, Logan G; Wise, Frank W

    2015-11-01

    Self-similar fiber oscillators are a relatively new class of mode-locked lasers. In these lasers, the self-similar evolution of a chirped parabolic pulse in normally-dispersive passive, active, or dispersion-decreasing fiber (DDF) is critical. In active (gain) fiber and DDF, the novel role of local nonlinear attraction makes the oscillators fundamentally different from any mode-locked lasers considered previously. In order to reconcile the spectral and temporal expansion of a pulse in the self-similar segment with the self-consistency required by a laser cavity's periodic boundary condition, several techniques have been applied. The result is a diverse range of fiber oscillators which demonstrate the exciting new design possibilities based on the self-similar model. Here, we review recent progress on self-similar oscillators both in passive and active fiber, and extensions of self-similar evolution for surpassing the limits of rare-earth gain media. We discuss some key remaining research questions and important future directions. Self-similar oscillators are capable of exceptional performance among ultrashort pulsed fiber lasers, and may be of key interest in the development of future ultrashort pulsed fiber lasers for medical imaging applications, as well as for low-noise fiber-based frequency combs. Their uniqueness among mode-locked lasers motivates study into their properties and behaviors and raises questions about how to understand mode-locked lasers more generally.

  13. How can attosecond pulse train interferometry interrogate electron dynamics?

    Science.gov (United States)

    Arnold, C. L.; Isinger, M.; Busto, D.; Guénot, D.; Nandi, S.; Zhong, S.; Dahlström, J. M.; Gisselbrecht, M.; l'Huillier, A.

    2018-04-01

    Light pulses of sub-100 as (1 as=10-18 s) duration, with photon energies in the extreme-ultraviolet (XUV) spectral domain, represent the shortest event in time ever made and controlled by human beings. Their first experimental observation in 2001 has opened the door to investigating the fundamental dynamics of the quantum world on the natural time scale for electrons in atoms, molecules and solids and marks the beginning of the scientific field now called attosecond science.

  14. Vibrotactile sensory substitution for object manipulation: amplitude versus pulse train frequency modulation.

    Science.gov (United States)

    Stepp, Cara E; Matsuoka, Yoky

    2012-01-01

    Incorporating sensory feedback with prosthetic devices is now possible, but the optimal methods of providing such feedback are still unknown. The relative utility of amplitude and pulse train frequency modulated stimulation paradigms for providing vibrotactile feedback for object manipulation was assessed in 10 participants. The two approaches were studied during virtual object manipulation using a robotic interface as a function of presentation order and a simultaneous cognitive load. Despite the potential pragmatic benefits associated with pulse train frequency modulated vibrotactile stimulation, comparison of the approach with amplitude modulation indicates that amplitude modulation vibrotactile stimulation provides superior feedback for object manipulation.

  15. Integrate and fire pulse train automaton for QRS detection.

    Science.gov (United States)

    Nallathambi, Gabriel; Príncipe, José C

    2014-02-01

    Monitoring heart activity from electrocardiograms (ECG) is crucial to avoid unnecessary fatalities; therefore, detection of QRS complex is fundamental to automated ECG monitoring. Continuous, portable 24/7 ECG monitoring requires wireless technology with constraints on power, bandwidth, area, and resolution. In order to provide continuous remote monitoring of patients and fast transmission of data to medical personnel for instantaneous intervention, we propose a methodology that converts analog inputs into pulses for ultralow power implementation. The signal encoding scheme is the time-based integrate and fire (IF) sampler from which a set of signal descriptors in the pulse domain are proposed. Furthermore, a logical decision rule for QRS detection based on morphological checking is derived. The proposed decision logic depends exclusively on relational and logical operators resulting in ultrafast recognition and can be implemented using combinatorial logic hardware to guarantee power consumption orders of magnitude lower than any microprocessor device. The algorithm was evaluated using the MIT-BIH arrhythmia database and results show that our algorithm performance is comparable to the state-of-the art software-based detection.

  16. Generation of a chirp-free optical pulse train with tunable pulse width based on a polarization modulator and an intensity modulator.

    Science.gov (United States)

    Pan, Shilong; Yao, Jianping

    2009-07-15

    A simple method for the generation of a chirp-free optical pulse train with tunable pulse width using a polarization modulator (PolM) and a zero-chirp intensity modulator (IM) is proposed and demonstrated. In the proposed system, a light wave with its polarization direction oriented at an angle of 45 degrees with respect to the principal axis of the PolM is polarization modulated by a sinusoidal drive signal. An optical polarizer is connected after the PolM to convert the polarization-modulated signals to a pulse train with the main peaks having a narrow pulse width. Then, the main peaks are selected by the IM, leading to the generation of a short optical pulse train with a repetition rate that is identical to or twice the frequency of the sinusoidal drive signal, depending on the dc bias of the IM. The pulse width of the generated pulse is easily tuned by adjusting the phase modulation index of the PolM. An experiment is carried out, and a pulse train with a duty cycle as small as 8.16% is generated.

  17. Deexcitation of one-dimensional Rydberg atoms with a chirped train of half-cycle pulses

    International Nuclear Information System (INIS)

    Kopyciuk, T.

    2010-01-01

    A protocol for deexcitation of one-dimensional high Rydberg states with the use of a chirped train of half-cycle pulses is given. It is found that the parameters of the efficiently deexciting train are directly related to the phenomenon of the dynamical stabilization of the initial state. Finally, numerical calculations are presented to demonstrate the efficiency of the protocol. The protocol allows to deexcite Rydberg atoms to states lying just above the ground one.

  18. Frequency-Selective Fat Suppression Radiofrequency Pulse Train to Remove Olefinic Fats.

    Science.gov (United States)

    Abe, Takayuki

    2013-01-01

    CHESS pulse can suppress the signal originating from aliphatic fat protons but cannot suppress the signal from olefinic fat protons, which is near the resonance frequency of water protons. Adipose tissue contains various fat species; aliphatic fat comprises about 90 % and olefinic fat about 10 % of adipose tissue. Thus, CHESS pulse cannot be used to suppress the signal from adipose tissue completely. The purpose of this study was to find a method to suppress the signal from adipose tissue completely. The Fatsat train pulse, created with an arbitrary flip angle and insensitive to B1 inhomogeneity, was used. Because B1 inhomogeneity is larger on higher field magnetic resonance imaging, the fat suppression radiofrequency pulse needs to be B1-insensitive. To investigate a percentage of olefinic fat in adipose tissues, the excitation frequency of the Fatsat train pulse was varied from -240 to +400 Hz and the images and fat-suppressed images were obtained. The presence of olefinic fat comprising about 10 % of abdominal adipose tissue was identified. The result agreed with some previous papers. Complete fat suppression could be achieved by partial (10 %) inversion of longitudinal aliphatic fat magnetization and by canceling out the two fat magnetizations. The flip angle was identified to about 95°. In conclusion, the cause that the signal from adipose tissues cannot be suppressed completely has been found. Improved images that signals from adipose tissues were suppressed completely have been demonstrated. This technique can also be applied to several pulse sequences.

  19. Oscillatory pulses and wave trains in a bistable reaction-diffusion system with cross diffusion.

    Science.gov (United States)

    Zemskov, Evgeny P; Tsyganov, Mikhail A; Horsthemke, Werner

    2017-01-01

    We study waves with exponentially decaying oscillatory tails in a reaction-diffusion system with linear cross diffusion. To be specific, we consider a piecewise linear approximation of the FitzHugh-Nagumo model, also known as the Bonhoeffer-van der Pol model. We focus on two types of traveling waves, namely solitary pulses that correspond to a homoclinic solution, and sequences of pulses or wave trains, i.e., a periodic solution. The effect of cross diffusion on wave profiles and speed of propagation is analyzed. We find the intriguing result that both pulses and wave trains occur in the bistable cross-diffusive FitzHugh-Nagumo system, whereas only fronts exist in the standard bistable system without cross diffusion.

  20. Train of high-power femtosecond pulses: Probe wave in a gas of prepared atoms

    Science.gov (United States)

    Muradyan, Gevorg; Muradyan, Atom Zh.

    2009-09-01

    We present a method for generating a regular train of ultrashort optical pulses in a prepared two-level medium. The train develops from incident monochromatic probe radiation traveling in a medium of atoms, which are in a quantum mechanical superposition of dressed internal states. In the frame of linear theory for the probe radiation, the energy of individual pulses is an exponentially growing function of atom density and of interaction cross section. Pulse repetition rate is determined by the pump field’s generalized Rabi frequency and can be around 1 THz and greater. We also show that the terms, extra to the dipole approximation, endow the gas by a new property: nonsaturating dependence of refractive index on dressing monochromatic field intensity. Contribution of these nonsaturating terms can be compatible with the main dipole approximation term contribution in the wavelength region of about ten micrometers (the range of CO2 laser) or larger.

  1. Electrostrictive cross-phase modulation of periodic pulse trains in optical fibers.

    Science.gov (United States)

    Fellegara, A; Wabnitz, S

    1998-09-01

    Electrostriction-induced cross-phase modulation between subsequent bits of a nonreturn-to-zero pulse train in optical fibers leads to nonlinear frequency shifts of opposite sign for the 1's and the 0's. Direct experimental measurements of the electrostrictive and Kerr-induced nonlinear phase shift across the bit profiles agree well with the theoretical modeling.

  2. Wave fronts, pulses and wave trains in photoexcited superlattices behaving as excitable or oscillatory media

    International Nuclear Information System (INIS)

    Arana, J I; Bonilla, L L; Grahn, H T

    2011-01-01

    Undoped and strongly photoexcited semiconductor superlattices with field-dependent recombination behave as excitable or oscillatory media with spatially discrete nonlinear convection and diffusion. Infinitely long, dc-current-biased superlattices behaving as excitable media exhibit wave fronts with increasing or decreasing profiles, whose velocities can be calculated by means of asymptotic methods. These superlattices can also support pulses of the electric field. Pulses moving downstream with the flux of electrons can be constructed from their component wave fronts, whereas pulses advancing upstream do so slowly and experience saltatory motion: they change slowly in long intervals of time separated by fast transitions during which the pulses jump to the previous superlattice period. Photoexcited superlattices can also behave as oscillatory media and exhibit wave trains. (paper)

  3. Coherent population trapping in negatively charged self-assembled quantum dots using a train of femtosecond pulses

    OpenAIRE

    Kumar, Parvendra; Nakajima, Takashi

    2015-01-01

    We demonstrate the coherent population trapping in a single quantum dot and an ensemble of negatively charged quantum dots using a train of femtosecond pulses. Particularly in an ensemble of quantum dots, we show that the detrimental effects due to the inhomogeneous distribution of their properties can be minimized by appropriately choosing the pulse-train parameters and the magnetic-field strength in such a way that the electron-Zeeman splitting is an integer multiple of the pulse repetition...

  4. Direct generation of 81 nJ pulses and external compression to a subpicosecond regime with a 4.9 MHz chirped-pulse multipass-cavity Cr⁴⁺:forsterite oscillator.

    Science.gov (United States)

    Cankaya, Huseyin; Akturk, Selcuk; Sennaroglu, Alphan

    2011-05-01

    We report direct generation of 81 nJ chirped pulses from a room-temperature, Kerr lens mode-locked Cr⁴⁺:forsterite oscillator operating at 1258 nm. To increase the pulse energy, the pulse repetition rate of the short x-type resonator was lowered from 143 to 4.9 MHz by the addition of a q-preserving multipass cavity, which provided an additional effective optical path length of 59.4 m. The duration of the chirped pulses was around 5.5 ps with a spectral width of 21 nm. The pulses were externally compressed to 607 fs by using a diffraction grating pair. To our knowledge, this is the highest reported pulse energy directly generated from a room-temperature mode-locked Cr⁴⁺:forsterite laser.

  5. Ultrahigh-speed optical coherence tomography imaging and visualization of the embryonic avian heart using a buffered Fourier Domain Mode Locked laser.

    Science.gov (United States)

    Jenkins, M W; Adler, D C; Gargesha, M; Huber, R; Rothenberg, F; Belding, J; Watanabe, M; Wilson, D L; Fujimoto, J G; Rollins, A M

    2007-05-14

    The embryonic avian heart is an important model for studying cardiac developmental biology. The mechanisms that govern the development of a four-chambered heart from a peristaltic heart tube are largely unknown due in part to a lack of adequate imaging technology. Due to the small size and rapid motion of the living embryonic avian heart, an imaging system with high spatial and temporal resolution is required to study these models. Here, an optical coherence tomography (OCT) system using a buffered Fourier Domain Mode Locked (FDML) laser is applied for ultrahigh-speed non-invasive imaging of embryonic quail hearts at 100,000 axial scans per second. The high scan rate enables the acquisition of high temporal resolution 2D datasets (195 frames per second or 5.12 ms between frames) and 3D datasets (10 volumes per second). Spatio-temporal details of cardiac motion not resolvable using previous OCT technology are analyzed. Visualization and measurement techniques are developed to non-invasively observe and quantify cardiac motion throughout the brief period of systole (less than 50 msec) and diastole. This marks the first time that the preseptated embryonic avian heart has been imaged in 4D without the aid of gating and the first time it has been viewed in cross section during looping with extremely high temporal resolution, enabling the observation of morphological dynamics of the beating heart during systole.

  6. Ultrahigh-speed optical coherence tomography imaging and visualization of the embryonic avian heart using a buffered Fourier Domain Mode Locked laser

    Science.gov (United States)

    Jenkins, M. W.; Adler, D. C.; Gargesha, M.; Huber, R.; Rothenberg, F.; Belding, J.; Watanabe, M.; Wilson, D. L.; Fujimoto, J. G.; Rollins, A. M.

    2015-01-01

    The embryonic avian heart is an important model for studying cardiac developmental biology. The mechanisms that govern the development of a four-chambered heart from a peristaltic heart tube are largely unknown due in part to a lack of adequate imaging technology. Due to the small size and rapid motion of the living embryonic avian heart, an imaging system with high spatial and temporal resolution is required to study these models. Here, an optical coherence tomography (OCT) system using a buffered Fourier Domain Mode Locked (FDML) laser is applied for ultrahigh-speed non-invasive imaging of embryonic quail hearts at 100,000 axial scans per second. The high scan rate enables the acquisition of high temporal resolution 2D datasets (195 frames per second or 5.12 ms between frames) and 3D datasets (10 volumes per second). Spatio-temporal details of cardiac motion not resolvable using previous OCT technology are analyzed. Visualization and measurement techniques are developed to non-invasively observe and quantify cardiac motion throughout the brief period of systole (less than 50 msec) and diastole. This marks the first time that the preseptated embryonic avian heart has been imaged in 4D without the aid of gating and the first time it has been viewed in cross section during looping with extremely high temporal resolution, enabling the observation of morphological dynamics of the beating heart during systole. PMID:19546930

  7. Mitigation of mode partition noise in quantum-dash Fabry-Perot mode-locked lasers using Manchester encoding and balanced detection.

    Science.gov (United States)

    Chaibi, Mohamed Essghair; Bramerie, Laurent; Lobo, Sébastien; Peucheret, Christophe

    2017-07-10

    We propose the use of Manchester encoding in conjunction with balanced detection to overcome the mode partition noise (MPN) limit of quantum-dash Fabry-Perot mode-locked lasers (QD-MLLs) used as multi-wavelength sources in short-reach applications. The proposed approach is demonstrated for a 10-mode laser, each carrying a 10-Gb/s signal. We show that bit-error-rate floors as high as 10 -4 when traditional non-return-to-zero (NRZ) modulation is employed with a single-ended detection scheme can be pushed below 10 -9 thanks to the introduction of Manchester encoding together with balanced detection. The benefit of the scheme could be attributed to the spectral shift of the Manchester spectrum, resulting in a smaller overlap with the high-relative intensity noise (RIN) region present at low frequencies, and the use of balanced detection. We clarify the origin of the performance improvement through comparisons of single-ended and balanced detection and the use of a RIN emulation technique. We unambiguously show that the use of balanced detection plays the leading role in MPN mitigation enabled by Manchester modulation.

  8. Optimized saturation pulse train for human first-pass myocardial perfusion imaging at 7T.

    Science.gov (United States)

    Tao, Yuehui; Hess, Aaron T; Keith, Graeme A; Rodgers, Christopher T; Liu, Alexander; Francis, Jane M; Neubauer, Stefan; Robson, Matthew D

    2015-04-01

    To investigate whether saturation using existing methods developed for 3T imaging is feasible for clinical perfusion imaging at 7T, and to propose a new design of saturation pulse train for first-pass myocardial perfusion imaging at 7T. The new design of saturation pulse train consists of four hyperbolic-secant (HS8) radiofrequency pulses, whose peak amplitudes are optimized for a target range of static and transmit field variations and radiofrequency power deposition restrictions measured in the myocardium at 7T. The proposed method and existing methods were compared in simulation, phantom, and in vivo experiments. In healthy volunteer experiments without contrast agent, average saturation efficiency with the proposed method was 97.8%. This is superior to results from the three previously published methods at 86/95/90.8%. The first series of human first-pass myocardial perfusion images at 7T have been successfully acquired with the proposed method. Existing saturation methods developed for 3T imaging are not optimal for perfusion imaging at 7T. The proposed new design of saturation pulse train can saturate effectively, and with this method first-pass myocardial perfusion imaging is feasible in humans at 7T. © 2014 The Authors. Magnetic Resonance in Medicine Published by Wiley Periodicals, Inc. on behalf of International Society of Medicine in Resonance.

  9. Optimized Saturation Pulse Train for Human First-Pass Myocardial Perfusion Imaging at 7T

    Science.gov (United States)

    Tao, Yuehui; Hess, Aaron T; Keith, Graeme A; Rodgers, Christopher T; Liu, Alexander; Francis, Jane M; Neubauer, Stefan; Robson, Matthew D

    2015-01-01

    Purpose To investigate whether saturation using existing methods developed for 3T imaging is feasible for clinical perfusion imaging at 7T, and to propose a new design of saturation pulse train for first-pass myocardial perfusion imaging at 7T. Methods The new design of saturation pulse train consists of four hyperbolic-secant (HS8) radiofrequency pulses, whose peak amplitudes are optimized for a target range of static and transmit field variations and radiofrequency power deposition restrictions measured in the myocardium at 7T. The proposed method and existing methods were compared in simulation, phantom, and in vivo experiments. Results In healthy volunteer experiments without contrast agent, average saturation efficiency with the proposed method was 97.8%. This is superior to results from the three previously published methods at 86/95/90.8%. The first series of human first-pass myocardial perfusion images at 7T have been successfully acquired with the proposed method. Conclusion Existing saturation methods developed for 3T imaging are not optimal for perfusion imaging at 7T. The proposed new design of saturation pulse train can saturate effectively, and with this method first-pass myocardial perfusion imaging is feasible in humans at 7T. Magn Reson Med 73:1450–1456, 2015. © 2014 The Authors. Magnetic Resonance in Medicine Published by Wiley Periodicals, Inc. on behalf of International Society of Medicine in Resonance. PMID:24753130

  10. Generation of low-frequency drift pulse trains by direct modulation of a distributed-feedback laser array

    Science.gov (United States)

    Kuroda, Keiji; Yoshikuni, Yuzo

    2016-01-01

    We propose a simple method to generate low-frequency drift pulse trains by direct modulation of a laser diode system consisting of a distributed-feedback laser array and a semiconductor optical amplifier. We measure the temporal profiles, beat signals and spectra of pulses generated under three different sets of conditions. We found that low-frequency drift pulse trains are generated by application of a DC voltage to one of the laser diodes and a pulse voltage to the semiconductor optical amplifier.

  11. First observation of multi-pulse X-ray train via multi-collision laser Compton scattering

    International Nuclear Information System (INIS)

    Kuroda, R.; Toyokawa, H.; Yasumoto, M.; Ikeura-Sekiguchi, H.; Koike, M.; Yamada, K.; Yanagida, T.; Nakajyo, T.; Sakai, F.

    2009-01-01

    A compact hard X-ray source via laser Compton scattering (LCS) has been developed for biological and medical applications at the National Institute of Advanced Industrial Science and Technology (AIST) in Japan. The multi-collision LCS has been investigated in order to enhance the X-ray yields. The first observation of multi-pulse X-ray train with 6 pulses via the multi-collision LCS has been successfully demonstrated between the multi-bunch electron train with 6 bunches and the multi-pulse Ti:Sa laser train with 6 pulses. The 32 MeV electron train was generated from a Cs 2 Te photocathode rf gun with a multi-pulse UV laser and the S-band linac. The Ti:Sa laser train was obtained with the chirp pulse amplification (CPA) including the modified regenerative amplifier. The X-ray train with 6 pulses with 12.6 ns spacing was observed with the micro-channel plate (MCP). The maximum energy of the X-ray is analytically estimated to be about 24 keV and the total number of generated photons was calculated to be about 1.8x10 6 photons/train.

  12. Method to generate a pulse train of few-cycle coherent radiation

    Directory of Open Access Journals (Sweden)

    Bryant Garcia

    2016-09-01

    Full Text Available We develop a method to generate a long pulse train of few-cycle coherent radiation by modulating an electron beam with a high power laser. The large energy modulation disperses the beam in a radiating undulator and leads to the production of phase-locked few-cycle coherent radiation pulses. These pulses are produced at a high harmonic of the modulating laser, and are longitudinally separated by the modulating laser wavelength. We discuss an analytical model for this scheme and investigate the temporal and spectral properties of this radiation. This model is compared with numerical simulation results using the unaveraged code Puffin. We examine various harmful effects and how they might be avoided, as well as a possible experimental realization of this scheme.

  13. The limiting parameters of ultrashort pulses in a lanthanum beryllate laser

    Science.gov (United States)

    Demchuk, M. I.; Mikhailov, V. P.; Gilev, A. K.; Shkadarevich, A. P.; Stavrov, A. A.

    1985-06-01

    The conditions of passive mode-locking in a lanthanum beryllate laser (La2Be2O5 - Nd/+/) have been investigated experimentally. The effect of the nonlinear parameters of the passive shutter on the duration of the pulses was studied in detail. A minimum pulse duration of about 4 ps was obtained using a passive shutter with a transmission coefficient of 30 percent for a laser energy of 3.0 megajoules.

  14. Multicompartment retinal ganglion cells response to high frequency bi-phasic pulse train stimulation: Simulation results.

    Science.gov (United States)

    Maturana, Matias I; Grayden, David B; Burkitt, Anthony N; Meffin, Hamish; Kameneva, Tatiana

    2013-01-01

    Retinal ganglion cells (RGCs) are the sole output neurons of the retina that carry information about a visual scene to the brain. By stimulating RGCs with electrical stimulation, it is possible to elicit a sensation of light for people with macular degeneration or retinitis pigmentosa. To investigate the responses of RGCs to high frequency bi-phasic pulse train stimulation, we use previously constrained models of multi-compartment OFF RGCs. The morphologies of mouse RGCs are taken from the Chalupa set of the NeuroMorpho database. The cell models are divided into compartments representing the dendrites, soma and axon that vary between the cells. A total of 132 cells are simulated in the NEURON environment. Results show that the cell morphology plays an important role in the response characteristics of the cell to high frequency bi-phasic pulse train stimulation.

  15. Recurrent pulse trains in the solar hard X-ray flare of 1980 June 7

    International Nuclear Information System (INIS)

    Kiplinger, A.L.; Dennis, B.R.; Frost, K.J.; Orwig, L.E.

    1983-01-01

    This study presents a detailed examination of the solar hard X-ray and γ-ray flare of 1980 June 7 as seen by the Hard X-Ray Burst Spectrometer on SMM. The hard X-ray profile is most unusual in that it is characterized by an initial pulse train of seven intense hard X-ray spikes. However, the event is unique among the 6300 events observed by HXRBS in that the temporal signature of this pulse train recurs twice during the flare. Such signatures of temporal stability in impulsive solar flares have not been observed before. Examinations of the hard X-ray data in conjunction with radio and γ-ray observations show that the 28--480 keV X-ray emission is simultaneous with the 17 GHz microwave fluxes within 128 ms and that the 3.5--6.5 MeV prompt γ-ray line emission is coincident with secondary maxima of the microwave and X-ray fluxes. Studies of the temporal and spectral properties of the pulses indicate that the pulses are not produced by purely reversible processes, and that if the source is oscillatory, it is not a high quality oscillator. Although the absence of spatially resolved hard X-ray observations leaves other possibilities open, a parameterization of the event as a set of seven sequentially firing loops is presented that offers many satisfying explanations of the observations

  16. Design and Characteristic Analysis of Multicarrier Chaotic Phase Coded Radar Pulse Train Signal

    OpenAIRE

    Huang, Qiongdan; Li, Yong; Zeng, Yaoping; Fu, Yinjuan

    2014-01-01

    By introducing phase code into multicarrier orthogonal frequency division multiplex signal, the multicarrier phase coded (MCPC) radar signal possesses a good spectrum utilization rate and can achieve a good combination of narrowband and wideband processing. Radar pulse train signal not only reserves the high range resolution of monopulse signal, but also has the same velocity resolution performance as continuous wave signal does. In this study, we use the chaotic biphase code generated by Che...

  17. Vibrotactile Sensory Substitution for Object Manipulation: Amplitude versus Pulse Train Frequency Modulation

    OpenAIRE

    Stepp, Cara E.; Matsuoka, Yoky

    2011-01-01

    Incorporating sensory feedback with prosthetic devices is now possible, but the optimal methods of providing such feedback are still unknown. The relative utility of amplitude and pulse train frequency modulated stimulation paradigms for providing vibrotactile feedback for object manipulation was assessed in 10 participants. The two approaches were studied during virtual object manipulation using a robotic interface as a function of presentation order and a simultaneous cognitive load. Despit...

  18. Pulse-train Stimulation of Primary Somatosensory Cortex Blocks Pain Perception in Tail Clip Test.

    Science.gov (United States)

    Lee, Soohyun; Hwang, Eunjin; Lee, Dongmyeong; Choi, Jee Hyun

    2017-04-01

    Human studies of brain stimulation have demonstrated modulatory effects on the perception of pain. However, whether the primary somatosensory cortical activity is associated with antinociceptive responses remains unknown. Therefore, we examined the antinociceptive effects of neuronal activity evoked by optogenetic stimulation of primary somatosensory cortex. Optogenetic transgenic mice were subjected to continuous or pulse-train optogenetic stimulation of the primary somatosensory cortex at frequencies of 15, 30, and 40 Hz, during a tail clip test. Reaction time was measured using a digital high-speed video camera. Pulse-train optogenetic stimulation of primary somatosensory cortex showed a delayed pain response with respect to a tail clip, whereas no significant change in reaction time was observed with continuous stimulation. In response to the pulse-train stimulation, video monitoring and local field potential recording revealed associated paw movement and sensorimotor rhythms, respectively. Our results show that optogenetic stimulation of primary somatosensory cortex at beta and gamma frequencies blocks transmission of pain signals in tail clip test.

  19. Wide-Range Temperature Sensors with High-Level Pulse Train Output

    Science.gov (United States)

    Hammoud, Ahmad; Patterson, Richard L.

    2009-01-01

    Two types of temperature sensors have been developed for wide-range temperature applications. The two sensors measure temperature in the range of -190 to +200 C and utilize a thin-film platinum RTD (resistance temperature detector) as the temperature-sensing element. Other parts used in the fabrication of these sensors include NPO (negative-positive- zero) type ceramic capacitors for timing, thermally-stable film or wirewound resistors, and high-temperature circuit boards and solder. The first type of temperature sensor is a relaxation oscillator circuit using an SOI (silicon-on-insulator) operational amplifier as a comparator. The output is a pulse train with a period that is roughly proportional to the temperature being measured. The voltage level of the pulse train is high-level, for example 10 V. The high-level output makes the sensor less sensitive to noise or electromagnetic interference. The output can be read by a frequency or period meter and then converted into a temperature reading. The second type of temperature sensor is made up of various types of multivibrator circuits using an SOI type 555 timer and the passive components mentioned above. Three configurations have been developed that were based on the technique of charging and discharging a capacitor through a resistive element to create a train of pulses governed by the capacitor-resistor time constant. Both types of sensors, which operated successfully over the wide temperature range, have potential use in extreme temperature environments including jet engines and space exploration missions.

  20. Predictions of psychophysical measurements for sinusoidal amplitude modulated (SAM) pulse-train stimuli from a stochastic model.

    Science.gov (United States)

    Xu, Yifang; Collins, Leslie M

    2007-08-01

    Two approaches have been proposed to reduce the synchrony of the neural response to electrical stimuli in cochlear implants. One approach involves adding noise to the pulse-train stimulus, and the other is based on using a high-rate pulse-train carrier. Hypotheses regarding the efficacy of the two approaches can be tested using computational models of neural responsiveness prior to time-intensive psychophysical studies. In our previous work, we have used such models to examine the effects of noise on several psychophysical measures important to speech recognition. However, to date there has been no parallel analytic solution investigating the neural response to the high-rate pulse-train stimuli and their effect on psychophysical measures. This work investigates the properties of the neural response to high-rate pulse-train stimuli with amplitude modulated envelopes using a stochastic auditory nerve model. The statistics governing the neural response to each pulse are derived using a recursive method. The agreement between the theoretical predictions and model simulations is demonstrated for sinusoidal amplitude modulated (SAM) high rate pulse-train stimuli. With our approach, predicting the neural response in modern implant devices becomes tractable. Psychophysical measurements are also predicted using the stochastic auditory nerve model for SAM high-rate pulse-train stimuli. Changes in dynamic range (DR) and intensity discrimination are compared with that observed for noise-modulated pulse-train stimuli. Modulation frequency discrimination is also studied as a function of stimulus level and pulse rate. Results suggest that high rate carriers may positively impact such psychophysical measures.

  1. Self-stabilizing optical clock pulse-train generator using SOA and saturable absorber for asynchronous optical packet processing.

    Science.gov (United States)

    Nakahara, Tatsushi; Takahashi, Ryo

    2013-05-06

    We propose a novel, self-stabilizing optical clock pulse-train generator for processing preamble-free, asynchronous optical packets with variable lengths. The generator is based on an optical loop that includes a semiconductor optical amplifier (SOA) and a high-extinction spin-polarized saturable absorber (SA), with the loop being self-stabilized by balancing out the gain and absorption provided by the SOA and SA, respectively. The optical pulse train is generated by tapping out a small portion of a circulating seed pulse. The convergence of the generated pulse energy is enabled by the loop round-trip gain function that has a negative slope due to gain saturation in the SOA. The amplified spontaneous emission (ASE) of the SOA is effectively suppressed by the SA, and a backward optical pulse launched into the SOA enables overcoming the carrier-recovery speed mismatch between the SOA and SA. Without external control for the loop gain, a stable optical pulse train consisting of more than 50 pulses with low jitter is generated from a single 10-ps seed optical pulse even with a variation of 10 dB in the seed pulse intensity.

  2. BOLD-fMRI response vs. transcranial magnetic stimulation (TMS) pulse-train length: testing for linearity.

    Science.gov (United States)

    Bohning, Daryl E; Shastri, Ananda; Lomarev, Mikhail P; Lorberbaum, Jeffrey P; Nahas, Ziad; George, Mark S

    2003-03-01

    To measure motor and auditory cortex blood oxygenation level-dependent (BOLD) functional magnetic resonance imaging (fMRI) response to impulse-like transcranial magnetic stimulation (TMS) pulses as a function of train length. Interleaved with fMRI at 1.5 T, TMS pulses 0.3-msec long were applied at 1 Hz to the motor cortex area for thumb. Six subjects were studied in a TR = 1 second session administering trains of 1, 2, 4, 8, and 16 pulses, and a TR = 3 seconds session administering trains of 1, 2, 4, 8, 16, and 24 pulses. A simple hemodynamic model with finite recovery and saturation was used to quantitatively characterize the BOLD-fMRI response as a function of train length. In both the activations directly induced in motor cortex by TMS and the indirect activations in auditory cortex caused by the sound of the TMS coil firing, the BOLD-fMRI responses to multiple pulses were well described by a summation of single-pulse impulse functions. Up to 24 discrete pulses, BOLD-fMRI response to 1 Hz TMS in both motor cortex and auditory cortex were consistent with a linear increase in amplitude and length with train length, possibly suggesting that stimuli of 1 to 2 seconds may be too long to represent impulses. Copyright 2003 Wiley-Liss, Inc.

  3. Studies to assess the effect of pet training aids, specifically remote static pulse systems, on the welfare of domestic dogs: field study of dogs in training

    OpenAIRE

    Cooper, Jonathan; Cracknell, Nina; Hardiman, Jessica; Mills, Daniel

    2013-01-01

    The project had a single aim, namely to assess the impact of use of remote static pulse electric training aids (e-collars) during the training of dogs in comparison to dogs referred for similar behavioural problems but without e-collar training. The specific objective was to use appropriate behavioural and physiological measures to make inferences about the welfare of subjects including their aversion and anxiety during and following training. A secondary objective was to evaluate the efficac...

  4. Psychophysical recovery from pulse-train forward masking in electric hearing

    Science.gov (United States)

    Nelson, David A.; Donaldson, Gail S.

    2002-12-01

    Psychophysical pulse-train forward-masking (PTFM) recovery functions were measured in fifteen subjects with the Nucleus mini-22 cochlear implant and six subjects with the Clarion cochlear implant. Masker and probe stimuli were 500-Hz trains of 200- or 77-μs/phase biphasic current pulses. Electrode configurations were bipolar for Nucleus subjects and monopolar for Clarion subjects. Masker duration was 320 ms. Probe duration was either 10 ms or 30 ms. Recovery functions were measured for a high-level masker on a middle electrode in all 21 subjects, on apical and basal electrodes in 7 of the Nucleus and 3 of the Clarion subjects, and for multiple masker levels on the middle electrode in 8 Nucleus subjects and 6 Clarion subjects. Recovery functions were described by an exponential process in which threshold shift (in μA) decreased exponentially with increasing time delay between the offset of the masker pulse train and the offset of the probe pulse train. All but 3 of the 21 subjects demonstrated recovery time constants on a middle electrode that were less than 95 ms. The mean time constant for these 18 subjects was 54 ms (s.d. 17 ms). Three other subjects tested on three electrodes exhibited time constants larger than 95 ms from an apical electrode only. Growth-of-masking slopes depended upon time delay, as expected from an exponential recovery process, i.e., progressively shallower slopes were observed at time delays of 10 ms and 50 ms. Recovery of threshold shift (in μA) for PTFM in electrical hearing behaves in the same way as recovery of threshold shift (in dB) for pure-tone forward masking in acoustic hearing. This supports the concept that linear microamps are the electrical equivalent of acoustic decibels. Recovery from PTFM was not related to speech recognition in a simple manner. Three subjects with prolonged PTFM recovery demonstrated poor speech scores. The remaining subjects with apparently normal PTFM recovery demonstrated speech scores ranging from

  5. High-power pre-chirp managed amplification of femtosecond pulses at high repetition rates

    International Nuclear Information System (INIS)

    Liu, Yang; Li, Wenxue; Zhao, Jian; Bai, Dongbi; Luo, Daping; Zeng, Heping

    2015-01-01

    Femtosecond pulses at 250 MHz repetition rate from a mode-locked fiber laser are amplified to high power in a pre-chirp managed amplifier. The experimental strategy offers a potential towards high-power ultrashort laser pulses at high repetition rates. By investigating the laser pulse evolution in the amplification processes, we show that self-similar evolution, finite gain bandwidth and mode instabilities determine pulse characteristics in different regimes. Further average power scaling is limited by the mode instabilities. Nevertheless, this laser system enables us to achieve sub-50 fs pulses with an average power of 93 W. (letter)

  6. Noise-like pulse generation in an ytterbium-doped fiber laser using tungsten disulphide

    Science.gov (United States)

    Zhang, Wenping; Song, Yanrong; Guoyu, Heyang; Xu, Runqin; Dong, Zikai; Li, Kexuan; Tian, Jinrong; Gong, Shuang

    2017-12-01

    We demonstrated the noise-like pulse (NLP) generation in an ytterbium-doped fiber (YDF) laser with tungsten disulphide (WS2). Stable fundamental mode locking and second-order harmonic mode locking were observed. The saturable absorber (SA) was a WS2-polyvinyl alcohol film. The modulation depth of the WS2 film was 2.4%, and the saturable optical intensity was 155 MW cm-2. Based on this SA, the fundamental NLP with a pulse width of 20 ns and repetition rate of 7 MHz were observed. The autocorrelation trace of output pulses had a coherent spike, which came from NLP. The average pulse width of the spike was 550 fs on the top of a broad pedestal. The second-order harmonic NLP had a spectral bandwidth of 1.3 nm and pulse width of 10 ns. With the pump power of 400 mW, the maximum output power was 22.2 mW. To the best of our knowledge, this is the first time a noise-like mode locking in an YDF laser based on WS2-SA in an all normal dispersion regime was obtained.

  7. Low frequency, ca. 40 Hz, pulse trains recorded in the humpback whale assembly in Hawaii.

    Science.gov (United States)

    Darling, James D

    2015-11-01

    During studies of humpback whale song and social sounds in Hawaii, bouts of low frequency (ca. 40 Hz) pulses were periodically recorded. One example was made near an active group of eight adults (included 22 bouts, 2-13 s long, over 90 min); another close to an adult male-female pair (12 bouts, 9-93 s long, over 22 min). The mean peak and center frequencies (39 to 40 Hz) and bandwidth (13 Hz) were similar in both, but the organization of the pulses differed. Song components, social sounds, bubble trains, or other species do not provide a ready explanation for this sound.

  8. High-efficiency intracavity second-harmonic enhancement for a few-cycle laser pulse train

    International Nuclear Information System (INIS)

    Cai, Yi; Xu, Shixiang; Zeng, Xuanke; Zou, Da; Li, Jingzhen

    2012-01-01

    This paper presents an intracavity second-harmonic (SH) enhancement technology without the need of input impedance-matching for optimal coupling between the cavity and its input frequency comb. More than 10% SH energy conversion efficiency is available, thus the power of the SH frequency comb can be enhanced beyond 100 relative to single-pass SH generation. Compared with a conventional passive enhancing cavity, for the purpose of high power enhancement, our scheme can operate at much lower finesse and thus broader bandwidth so that it can support several-optical-cycle pulses more easily. If they have the same finesse, both methods perform with similar operating stability. The results show that our novel design is suitable for some applications which need a short wavelength, high intensity, and ultra-broad bandwidth pulse train. (paper)

  9. Properties of unipolar magnetic field pulse trains generated by lightning discharges

    Czech Academy of Sciences Publication Activity Database

    Kolmašová, Ivana; Santolík, Ondřej

    2013-01-01

    Roč. 40, č. 8 (2013), 1637–1641 ISSN 0094-8276 R&D Projects: GA ČR GA205/09/1253 Grant - others:Rada Programu interní podpory projektů mezinárodní spolupráce AV ČR(CZ) M100421206 Institutional support: RVO:68378289 Keywords : train of pulses * dart-stepped leader * K change Subject RIV: BL - Plasma and Gas Discharge Physics Impact factor: 4.456, year: 2013 http://onlinelibrary.wiley.com/doi/10.1002/grl.50366/abstract

  10. Even harmonic pulse train generation by cross-polarization-modulation seeded instability in optical fibers

    OpenAIRE

    Fatome, Julien; El Mansouri, Ibrahim; Blanchet, Jean-Luc; Pitois, Stéphane; Millot, Guy; Trillo, Stefano; Wabnitz, Stefan

    2012-01-01

    International audience; We show that, by properly adjusting the relative state of polarization of the pump and of a weak modulation, with a frequency such that at least one of its even harmonics falls within the band of modulation instability, one obtains a fully modulated wave at the second or higher even harmonic of the initial modulation. An application of this principle to the generation of a 80-GHz optical pulse train with high extinction ratio from a 40-GHz weakly modulated pump is expe...

  11. Temporal response properties of retinal ganglion cells in rd1 mice evoked by amplitude-modulated electrical pulse trains.

    Science.gov (United States)

    Ryu, Sang Baek; Ye, Jang Hee; Goo, Yong Sook; Kim, Chi Hyun; Kim, Kyung Hwan

    2010-12-01

    The electrophysiological properties of degenerated retinas responding to amplitude-modulated electrical pulse trains were investigated to provide a guideline for the development of a stimulation strategy for retinal prostheses. The activities of retinal ganglion cells (RGCs) in response to amplitude-modulated pulse trains were recorded from an in vitro model of retinal prosthesis, which consisted of an rd1 mouse retinal patch attached to a planar multielectrode array. The ability of the population activities of RGCs to effectively represent, or encode, the information on the visual intensity time series, when the intensity of visual input is transformed to pulse amplitudes, was investigated. An optimal pulse amplitude range was selected so that RGC firing rates increased monotonically and linearly. An approximately 10-Hz rhythm was observed in the field potentials from degenerated retinas, which resulted in a rhythmic burst of spontaneous spikes. Multiple peaks were present in poststimulus time histograms, with interpeak intervals corresponding to the oscillation frequency of the field potentials. Phase resetting of the field potential oscillation by stimulation was consistently observed. Despite a prominent alteration of the properties of electrically evoked firing with respect to normal retinas, RGC response strengths could be modulated by pulse amplitude. Accordingly, the temporal information of stimulation could be faithfully represented in the RGC firing patterns by an amplitude-modulated pulse train. The results suggest that pulse amplitude modulation is a feasible means of implementing a stimulation strategy for retinal prostheses, despite the marked change in the physiological properties of RGCs in degenerated retinas.

  12. On the 2nd order autocorrelation of an XUV attosecond pulse train

    International Nuclear Information System (INIS)

    Tzallas, P.; Benis, E.; Nikolopoulos, L.A.A.; Tsakiris, G.D.; Witte, K.; Charalambidis, P

    2005-01-01

    Full text: We present the first direct measurement of sub-fs light bunching that has been achieved, extending well established fs optical metrology to XUV as pulses. A mean train pulse duration of 780 as has been extracted through a 2 nd order autocorrelation approach, utilizing a nonlinear effect that is induced solely by the XUV radiation to be characterized. The approach is based on (i) a bisected spherical mirror XUV wavefront divider used as an autocorrelator and (ii) the two photon ionization of atomic He by a superposition of the 7 th to the 15 th harmonic of a Ti:sapph laser. The measured temporal mean width is more than twice its Fourier transform limited (FTL) value, in contrast to the as train pulse durations measured through other approaches, which where found much closer to the FTL values. We have investigated, and discuss here the origin of this discrepancy. An assessment of the validity of the 2 nd order AC approach for the broad band XUV radiation of as pulses is implemented through ab initio calculations (solution of the 3D TDSE of He in the presence of the superposition of the harmonic superposition) modeling the spectral and temporal response of the two-XUV-photon He ionization detector employed. It is found that both the spectral and temporal response are not affecting the measured duration. The mean width of the as train bursts is estimated from the spectral phases of the individual harmonics as they result from the rescattering model, taking into account the spatially modulated temporal width of the radiation due to the spatiotemporal intensity distribution of the driving field during the harmonic generation process. The measured value is found in reasonable agreement with the estimated duration. The method used for the 2 nd order AC in itself initiates further XUV-pump-XUV-probe studies of sub-fs-scale dynamics and at the same time becomes highly pertinent in connection with nonlinear experiments using XUV free - electron laser sources. Refs

  13. Sidemode suppression for coupled optoelectronic oscillator by optical pulse power feedforward.

    Science.gov (United States)

    Dai, Yitang; Wang, Ruixin; Yin, Feifei; Dai, Jian; Yu, Lan; Li, Jianqiang; Xu, Kun

    2015-10-19

    Multiple sidemodes have been observed in a coupled optoelectronic oscillator (COEO) when the contained actively mode-locked fiber ring laser employs erbium-doped fiber (EDF). We propose that such sidemodes can be suppressed significantly by an optical pulse power feedforward scheme, through which the mode-locked optical pulse is reversely intensity-modulated by itself, resulting in a fast power limiting. Experimentally we show that sidemodes are suppressed as much as 40 dB in a 10-GHz COEO. The additional noise induced by the power feedforward technique is analyzed numerically. We show that for a COEO with a typical cavity length, the feedforward contribution to final single-side band (SSB) noise is minor and neglectable.

  14. Coexistence of harmonic soliton molecules and rectangular noise-like pulses in a figure-eight fiber laser.

    Science.gov (United States)

    Huang, Yu-Qi; Hu, Zi-Ang; Cui, Hu; Luo, Zhi-Chao; Luo, Ai-Ping; Xu, Wen-Cheng

    2016-09-01

    We report the coexistence of high-order harmonic soliton molecules and rectangular noise-like pulses (NLP) in a figure-eight fiber laser mode-locked by a nonlinear amplifying loop mirror. The harmonic soliton molecule has a repetition rate of 936.6 MHz, corresponding to the 466th harmonics of the fundamental cavity repetition rate, with soliton separation of 16.5 ps. Meanwhile, the rectangular NLP operates at the fundamental repetition rate. In addition, these two types of pulses could be generated independently by manipulating the polarization controllers. The experimental results demonstrate an interesting operation regime of the fiber laser and contribute to enriching the dynamics of mode-locked pulses in fiber lasers.

  15. Spectral self-imaging effect by time-domain multilevel phase modulation of a periodic pulse train.

    Science.gov (United States)

    Caraquitena, José; Beltrán, Marta; Llorente, Roberto; Martí, Javier; Muriel, Miguel A

    2011-03-15

    We propose and analyze a novel (to our knowledge) approach to implement the spectral self-imaging effect of optical frequency combs. The technique is based on time-domain multilevel phase-only modulation of a periodic optical pulse train. The method admits both infinite- and finite-duration periodic pulse sequences. We show that the fractional spectral self-imaging effect allows one to reduce by an integer factor the comb frequency spacing. Numerical simulation results support our theoretical analysis.

  16. Spectral self-imaging effect by time-domain multilevel phase modulation of a periodic pulse train

    OpenAIRE

    Caraquitena Sales, José; Beltrán, Marta; Llorente, Roberto; Martí Sendra, Javier; Muriel, Miguel A.

    2011-01-01

    We propose and analyze a novel (to our knowledge) approach to implement the spectral self-imaging effect of optical frequency combs. The technique is based on time-domain multilevel phase-only modulation of a periodic optical pulse train. The method admits both infinite- and finite-duration periodic pulse sequences. We show that the fractional spectral self-imaging effect allows one to reduce by an integer factor the comb frequency spacing. Numerical simulation results support our theoretical...

  17. Coherent lidar modulated with frequency stepped pulse trains for unambiguous high duty cycle range and velocity sensing in the atmosphere

    DEFF Research Database (Denmark)

    Lindelöw, Per Jonas Petter; Mohr, Johan Jacob

    2007-01-01

    Range unambiguous high duty cycle coherent lidars can be constructed based on frequency stepped pulse train modulation, even continuously emitting systems could be envisioned. Such systems are suitable for velocity sensing of dispersed targets, like the atmosphere, at fast acquisition rates....... The lightwave synthesized frequency sweeper is a suitable generator yielding fast pulse repetition rates and stable equidistant frequency steps. Theoretical range resolution profiles of modulated lidars are presented....

  18. Study and realisation of a femtosecond dye laser operating at different wavelengths. Ultrashort pulses compression and amplification

    International Nuclear Information System (INIS)

    Georges, Patrick

    1989-01-01

    We present the study and the realization of a passively mode-locked dye laser producing pulses shorter than 100 femto-seconds (10 -13 s). In a ring cavity with an amplifier medium (Rhodamine 60) and a saturable absorber (DODCI), a sequence of four prisms controls the group velocity dispersion and allows the generation of very short pulses. Then we have studied the production of femtosecond pulses at other wavelengths directly from the femtosecond dye laser. For the first rime, 60 fs pulses at 685 nm and pulses shorter than 50 fs between 775 nm and 800 nm have been produced by passive mode locking. These near infrared pulses have been used to study the absorption saturation kinetics in semiconductors multiple quantum wells GaAs/GaAlAs. We have observed a singular behavior of the laser operating at 685 nm and analyzed the produced pulses in terms of optical solitons. To perform time resolved spectroscopy with shortest pulses, we have studied a pulse compressor and a multipass amplifier to increase the pulses energy. Pulses of 20 fs and 10 micro-joules (peak power: 0.5 GW) have been obtained at low repetition rate (10 Hz) and pulses of 16 fs and 0.6 micro-joules pulses have been generated at high repetition rate (11 kHz) using a copper vapor laser. These pulses have been used to study the absorption saturation kinetics of an organic dye (the Malachite Green). (author) [fr

  19. Electric pulse stimulation of cultured murine muscle cells reproduces gene expression changes of trained mouse muscle.

    Directory of Open Access Journals (Sweden)

    Nathalie Burch

    2010-06-01

    Full Text Available Adequate levels of physical activity are at the center of a healthy lifestyle. However, the molecular mechanisms that mediate the beneficial effects of exercise remain enigmatic. This gap in knowledge is caused by the lack of an amenable experimental model system. Therefore, we optimized electric pulse stimulation of muscle cells to closely recapitulate the plastic changes in gene expression observed in a trained skeletal muscle. The exact experimental conditions were established using the peroxisome proliferator-activated receptor gamma coactivator 1alpha (PGC-1alpha as a marker for an endurance-trained muscle fiber. We subsequently compared the changes in the relative expression of metabolic and myofibrillar genes in the muscle cell system with those observed in mouse muscle in vivo following either an acute or repeated bouts of treadmill exercise. Importantly, in electrically stimulated C2C12 mouse muscle cells, the qualitative transcriptional adaptations were almost identical to those in trained muscle, but differ from the acute effects of exercise on muscle gene expression. In addition, significant alterations in the expression of myofibrillar proteins indicate that this stimulation could be used to modulate the fiber-type of muscle cells in culture. Our data thus describe an experimental cell culture model for the study of at least some of the transcriptional aspects of skeletal muscle adaptation to physical activity. This system will be useful for the study of the molecular mechanisms that regulate exercise adaptation in muscle.

  20. Resonant amplification of magnetic domain-wall motion by a train of current pulses.

    Science.gov (United States)

    Thomas, Luc; Hayashi, Masamitsu; Jiang, Xin; Moriya, Rai; Rettner, Charles; Parkin, Stuart

    2007-03-16

    The current-induced motion of magnetic domain walls confined to nanostructures is of interest for applications in magnetoelectronic devices in which the domain wall serves as the logic gate or memory element. The injection of spin-polarized current below a threshold value through a domain wall confined to a pinning potential results in its precessional motion within the potential well. We show that by using a short train of current pulses, whose length and spacing are tuned to this precession frequency, the domain wall's oscillations can be resonantly amplified. This makes possible the motion of domain walls with much reduced currents, more than five times smaller than in the absence of resonant amplification.

  1. On-line statistical processing of radiation detector pulse trains with time-varying count rates

    International Nuclear Information System (INIS)

    Apostolopoulos, G.

    2008-01-01

    Statistical analysis is of primary importance for the correct interpretation of nuclear measurements, due to the inherent random nature of radioactive decay processes. This paper discusses the application of statistical signal processing techniques to the random pulse trains generated by radiation detectors. The aims of the presented algorithms are: (i) continuous, on-line estimation of the underlying time-varying count rate θ(t) and its first-order derivative dθ/dt; (ii) detection of abrupt changes in both of these quantities and estimation of their new value after the change point. Maximum-likelihood techniques, based on the Poisson probability distribution, are employed for the on-line estimation of θ and dθ/dt. Detection of abrupt changes is achieved on the basis of the generalized likelihood ratio statistical test. The properties of the proposed algorithms are evaluated by extensive simulations and possible applications for on-line radiation monitoring are discussed

  2. Attosecond electron pulse trains and quantum state reconstruction in ultrafast transmission electron microscopy

    Science.gov (United States)

    Priebe, Katharina E.; Rathje, Christopher; Yalunin, Sergey V.; Hohage, Thorsten; Feist, Armin; Schäfer, Sascha; Ropers, Claus

    2017-12-01

    Ultrafast electron and X-ray imaging and spectroscopy are the basis for an ongoing revolution in the understanding of dynamical atomic-scale processes in matter. The underlying technology relies heavily on laser science for the generation and characterization of ever shorter pulses. Recent findings suggest that ultrafast electron microscopy with attosecond-structured wavefunctions may be feasible. However, such future technologies call for means to both prepare and fully analyse the corresponding free-electron quantum states. Here, we introduce a framework for the preparation, coherent manipulation and characterization of free-electron quantum states, experimentally demonstrating attosecond electron pulse trains. Phase-locked optical fields coherently control the electron wavefunction along the beam direction. We establish a new variant of quantum state tomography—`SQUIRRELS'—for free-electron ensembles. The ability to tailor and quantitatively map electron quantum states will promote the nanoscale study of electron-matter entanglement and new forms of ultrafast electron microscopy down to the attosecond regime.

  3. Bio-effects of repetitively pulsed ultra-fast distributed feedback dye lasers

    International Nuclear Information System (INIS)

    Khan, N.; Ahmad, M.I.; Sheikh, A.

    1999-01-01

    Results of experimental study showing an unexpected rise in pulses of distributed feedback dye laser (DFDL) output due to temperature accumulation in dye cell during passively Q-Switched, a Mode-locked operation is reported. This unintended increase in number of pulse duration, per pulse energy may cause side-effects when used for selective photo thermolysis. To probe this phenomenon most commonly dye was excited with 10 to 20 pulses of second harmonic of a passively Q-Switched and Mode-locked Nd-YaG laser. The outputs of DFDL and Nd:YaG laser were recorded by Imacon 675-streak camera. The peak of DFDL output pulses was found delayed proportionally from the peak of the NYAG pulses by more than one inter-pulse period of excitation laser. A computer program was used to simulate the experimentally measured delay to estimate thermal decay constants and energy retained by the medium to determine the amount of incremental fluctuations in output. The delay between peaks of Nd:YAG (input) and DFDL(output) pulses was found to vary from 10 to 14 nanoseconds for various cavity lengths. It was found that for smaller inter-pulse periods the effect of gradual build-up satisfies the threshold conditions for some of the pulses that otherwise can not. This may lead to unintended increase in energy fluence causing overexposure-induced side-effects. (author)

  4. Studies to assess the effect of pet training aids specifically remote static pulse systems on the welfare of domestic dogs

    OpenAIRE

    Cooper, Jonathan; Wright, Hannah; Mills, Daniel; Casey, Rachel; Blackwell, Emily; Van Driel, Katja; Lines, Jeff

    2013-01-01

    This project assessed the welfare of dogs trained with pet training aids, specifically remote static pulse collar systems (e-collars). Previous work has focused on a very limited number of devices in a very limited range of contexts and the evidence of the impact of such devices on dog's overall quality of life is inconclusive. Project AW1402 aimed to assess the physical characteristics of the e-collars and the physiological, behavioural and psychological consequences of their use in dog trai...

  5. Changes in auditory nerve responses across the duration of sinusoidally amplitude-modulated electric pulse-train stimuli.

    Science.gov (United States)

    Hu, Ning; Miller, Charles A; Abbas, Paul J; Robinson, Barbara K; Woo, Jihwan

    2010-12-01

    Response rates of auditory nerve fibers (ANFs) to electric pulse trains change over time, reflecting substantial spike-rate adaptation that depends on stimulus parameters. We hypothesize that adaptation affects the representation of amplitude-modulated pulse trains used by cochlear prostheses to transmit speech information to the auditory system. We recorded cat ANF responses to sinusoidally amplitude-modulated (SAM) trains with 5,000 pulse/s carriers. Stimuli delivered by a monopolar intracochlear electrode had fixed modulation frequency (100 Hz) and depth (10%). ANF responses were assessed by spike-rate measures, while representation of modulation was evaluated by vector strength (VS) and the fundamental component of the fast Fourier transform (F(0) amplitude). These measures were assessed across the 400 ms duration of pulse-train stimuli, a duration relevant to speech stimuli. Different stimulus levels were explored and responses were categorized into four spike-rate groups to assess level effects across ANFs. The temporal pattern of rate adaptation to modulated trains was similar to that of unmodulated trains, but with less rate adaptation. VS to the modulator increased over time and tended to saturate at lower spike rates, while F(0) amplitude typically decreased over time for low driven rates and increased for higher driven rates. VS at moderate and high spike rates and degree of F(0) amplitude temporal changes at low and moderate spike rates were positively correlated with the degree of rate adaptation. Thus, high-rate carriers will modify the ANF representation of the modulator over time. As the VS and F(0) measures were sensitive to adaptation-related changes over different spike-rate ranges, there is value in assessing both measures.

  6. Influence of noise amplification on generation of regular short pulse trains in optical fibre pumped by intensity-modulated CW radiation.

    Science.gov (United States)

    Kobtsev, Sergey M; Smirnov, Sergey V

    2008-05-12

    For the first time the influence of noise amplification on decay of modulated continuous-wave pumping into a pulse series in an optical fiber is considered. Dependence of noise-to-signal ratio in pulse train at fibre exit on initial modulation depth obtained both analytically and by means of numerical simulations. The minimum modulation frequency is estimated which leads to a regular pulse train formation from CW pumping.

  7. Layout of NALM fiber laser with adjustable peak power of generated pulses.

    Science.gov (United States)

    Smirnov, Sergey; Kobtsev, Sergey; Ivanenko, Alexey; Kokhanovskiy, Alexey; Kemmer, Anna; Gervaziev, Mikhail

    2017-05-01

    The Letter proposes a new layout of a passively mode-locked fiber laser based on a nonlinear amplifying loop mirror (NALM) with two stretches of active fiber and two independently controlled pump modules. In contrast with conventional NALM configurations using a single piece of active fiber that yields virtually constant peak power, the proposed novel laser features larger than a factor of 2 adjustment range of peak power of generated pulses. The proposed layout also provides independent adjustment of duration and peak power of generated pulses as well as power-independent control of generated pulse spectral width impossible in NALM lasers with a single piece of active fiber.

  8. Influence of aerobic exercise training on post-exercise responses of aortic pulse pressure and augmentation pressure in postmenopausal women

    Directory of Open Access Journals (Sweden)

    Nobuhiko eAkazawa

    2015-10-01

    Full Text Available Central arterial blood pressure (BP is more predictive of future cardiovascular events than is brachial BP because it reflects the BP load imposed on the left ventricle with greater accuracy. However, little is known about the effects of exercise training on central hemodynamic response to acute exercise. The purpose of the present study was to determine the influence of an aerobic exercise regimen on the response of aortic BP after a single aerobic exercise in postmenopausal women. Nine healthy postmenopausal women (age: 61 ± 2 years participated in a 12-week aerobic exercise training regimen. Before and after the training, each subjects performed a single bout of cycling at ventilatory thresholds for 30 min. We evaluated the post-exercise aortic BP response, which was estimated via the general transfer function from applanation tonometry. After the initial pre-training aerobic exercise session, aortic BP did not change significantly: however, aortic pulse pressure and augmentation pressure were significantly attenuated after the single aerobic exercise session following the 12-week training regimen. The present study demonstrated that a regular aerobic exercise training regimen induced the post-exercise reduction of aortic pulse pressure and augmentation pressure. Regular aerobic exercise training may enhance post-exercise reduction in aortic BP.

  9. Transformation of the frequency-modulated continuous-wave field into a train of short pulses by resonant filters

    Science.gov (United States)

    Shakhmuratov, R. N.

    2017-03-01

    The resonant filtering method transforming the frequency-modulated radiation field into a train of short pulses is proposed to be applied in the optical domain. Effective frequency modulation can be achieved by using an electro-optic modulator. Due to frequency modulation, a narrow-spectrum cw radiation field is seen by the resonant filter as a comb of equidistant spectral components separated by the modulation frequency. Tuning a narrow-bandwidth filter in resonance with the n th spectral component of the comb transforms the radiation field into bunches of pulses, with n pulses in each bunch. The transformation is explained by the interference of the coherently scattered resonant component of the field with the whole comb. Constructive interference results in the formation of pulses, while destructive interference is seen as dark windows between pulses. It is indicated that the optimal thickness of the resonant filter is several orders of magnitude smaller than the necessary thickness of the dispersive filters used before in the optical domain to produce short pulses from the frequency-modulated field.

  10. Comparison of Monolithic Optical Frequency Comb Generators Based on Passively Mode-Locked Lasers for Continuous Wave mm-Wave and Sub-THz Generation

    DEFF Research Database (Denmark)

    Criado, A. R.; de Dios, C.; Acedo, P.

    2012-01-01

    is carried out based on an automated measurement system that systematically evaluates the dynamic characteristics of the devices, focusing on the figures of merit that define the optimum performance of a pulsed laser source when considered as an OFCG. Sub-THz signals generated with both devices at 60 GHz...... topologies that can be used for the implementation of photonic integrated sub-THz CW generation....

  11. Dying Pulse Trains in Cygnus XR-1: Initial Results of X-Ray Searches

    Science.gov (United States)

    Dolan, Joseph F.

    2003-01-01

    Dying pulse trains (DPT's) are a signature of a black hole as described by general relativity. Detecting DPT's would establish the existence of black holes by ruling out more exotic objects in systems in which a neutron star or white dwarf component has already been excluded by maximum mass arguments. The positive identification of a black hole would also be an additional test of general relativity. Two possible DPT's were detected in W photometry of Cygnus XR-1, the leading candidate for a stellar mass sized BH, in 3 hours of observational data. A search of X-ray photometry of Cygnus XR-1 from the Ross1 X-ray Timing Explorer (RXTE) has begun. No DPT's have been detected in the first 4 hours of data searched. Because of the low event rate detected in the W data, these initial results are consistent with such disparate scenarios as the rate of DPT occurrence being dependent on the luminosity state of the system; or being more difficult to detect in the X-ray region relative to the W region; or occurring at the same rate in the W and X-ray regions; or even not occurring at all from Cygnus XR-1. The search for DPT's in RXTE photometry is continuing.

  12. Self-organization of waves and pulse trains by molecular motors in cellular protrusions

    Science.gov (United States)

    Yochelis, A.; Ebrahim, S.; Millis, B.; Cui, R.; Kachar, B.; Naoz, M.; Gov, N. S.

    2015-01-01

    Actin-based cellular protrusions are an ubiquitous feature of cells, performing a variety of critical functions ranging from cell-cell communication to cell motility. The formation and maintenance of these protrusions relies on the transport of proteins via myosin motors, to the protrusion tip. While tip-directed motion leads to accumulation of motors (and their molecular cargo) at the protrusion tip, it is observed that motors also form rearward moving, periodic and isolated aggregates. The origins and mechanisms of these aggregates, and whether they are important for the recycling of motors, remain open puzzles. Motivated by novel myosin-XV experiments, a mass conserving reaction-diffusion-advection model is proposed. The model incorporates a non-linear cooperative interaction between motors, which converts them between an active and an inactive state. Specifically, the type of aggregate formed (traveling waves or pulse-trains) is linked to the kinetics of motors at the protrusion tip which is introduced by a boundary condition. These pattern selection mechanisms are found not only to qualitatively agree with empirical observations but open new vistas to the transport phenomena by molecular motors in general. PMID:26335545

  13. Extension of supercontinuum spectrum, generated in polarization-maintaining photonic crystal fiber, using chirped femtosecond pulses

    Science.gov (United States)

    Vengelis, Julius; Jarutis, Vygandas; Sirutkaitis, Valdas

    2018-01-01

    We present results of experimental and numerical investigation of supercontinuum (SC) generation in polarization-maintaining photonic crystal fiber (PCF) using chirped femtosecond pulses. The initial unchirped pump pulse source was a mode-locked Yb:KGW laser generating 52-nJ energy, 110-fs duration pulses at 1030 nm with a 76-MHz repetition rate. The nonlinear medium was a 32-cm-long polarization-maintaining PCF manufactured by NKT Photonics A/S. We demonstrated the influence of pump pulse chirp on spectral characteristics of a SC. We showed that by chirping pump pulses positively or negatively one can obtain a broader SC spectrum than in the case of unchirped pump pulses at the same peak power. Moreover, the extension can be controlled by changing the amount of pump pulse chirp. Numerical simulation results also indicated that pump pulse chirp yields an extension of SC spectrum.

  14. Analytical identification of soliton dynamics in normal-dispersion passively mode-locked fiber lasers: from dissipative soliton to dissipative soliton resonance.

    Science.gov (United States)

    Lin, Wei; Wang, Simin; Xu, Shanhui; Luo, Zhi-Chao; Yang, Zhongmin

    2015-06-01

    A combined analytical approach to classify soliton dynamics from dissipative soliton to dissipative soliton resonance (DSR) is developed based on the established laser models. The approach, derived from two compatible analytical solutions to the complex cubic-quintic Ginzburg-Landau equation (CQGLE), characterizes the pulse evolution process from both algebraic and physical points of view. The proposed theory is proved to be valid in real world laser oscillators according to numerical simulations, and potentially offers guideline on the design of DSR cavity configurations.

  15. Ultra-high speed all-optical signal processing using silicon waveguides and a carbon nanotubes based mode-locked laser

    DEFF Research Database (Denmark)

    Ji, Hua

    for demultiplexing of 1.28 Tbit/s optical time division multiplexing data signal is investigated. A sampling system for ultra-high speed signal waveforms based on nano-engineered silicon waveguide is explored. To set up a sampling source, using carbon nanotubes for generating ultra-short pulses is pursued. A silicon......This thesis concerns the use of nano-engineered silicon waveguides for ultra-high speed optical serial data signal processing. The fundamental nonlinear properties of nano-engineered silicon waveguides are characterized. Utilizing the nonlinear effect in nano-engineered silicon waveguides...

  16. In Vitro Photothermal Destruction of Cancer Cells Using Gold Nanorods and Pulsed-Train Near-Infrared Laser

    Directory of Open Access Journals (Sweden)

    Jui-Teng Lin

    2012-01-01

    Full Text Available We present a novel pulsed-train near-IR diode laser system with real-time temperature monitoring of the laser-heated cancer cell mixed in gold nanorod solution. Near-IR diode laser at 808 nm matching the gold nanorod absorption peak (with an aspect ratio about 4.0 was used in this study. Both surface and volume temperatures were measured and kept above 43°C, the temperature for cancer cells destruction. The irradiation time needed in our pulsed-train system with higher laser fluence for killing the cancel cells is about 1–3 minutes, much shorter than conventional methods (5–10 minutes. Cell viabilities in gold nanorod mixed and controlled solutions are studied by green fluorescence.

  17. Oscillation in Penetration Distance in a Train of Chemical Pulses Propagating in an Optically Constrained Narrowing Channel

    Science.gov (United States)

    Kitahata, Hiroyuki; Fujio, Kenji; Gorecki, Jerzy; Nakata, Satoshi; Igarashi, Yasuhiro; Gorecka, Agnieszka; Yoshikawa, Kenichi

    2009-09-01

    A chemical wave train propagating in a narrowing excitable channel surrounded by a nonexcitable field is investigated by using a photosensitive Belousov-Zhabotinsky (BZ) reaction. The considered geometry is created as a dark triangle surrounded by an illuminated area where the reaction is suppressed by the light-induced generation of bromide ion. For a low illumination level, a pulse train terminates at a constant position. However, as the light intensity increases, the position at which subsequent pulses disappear changes periodically, so that the period-doubling of penetration depth occurs. Two-dimensional simulations based on a modified Oregonator model for the photosensitive BZ reaction reproduce the essential features of the experimental observation.

  18. Measurement of cardiac output during exercise in healthy, trained humans using lithium dilution and pulse contour analysis

    International Nuclear Information System (INIS)

    Elliott, Adrian D; Skowno, Justin; Prabhu, Mahesh; Ansley, Les

    2012-01-01

    The aim of this study was to evaluate the use of pulse contour analysis calibrated with lithium dilution in a single device (LiDCO™) for measurement of cardiac output (.Q) during exercise in healthy volunteers. We sought to; (a) compare pulse contour analysis (PulseCO) and lithium indicator dilution (LiDCO) for the measurement of .Q during exercise, and (b) assess the requirement for recalibration of PulseCO with LiDCO during exercise. Ten trained males performed multi-stage cycling exercise at intensities below and above ventilatory threshold before constant load maximal exercise to exhaustion. Uncalibrated PulseCO .Q (.Q raw ) was compared to that calibrated with lithium dilution at baseline (.Q baseline ), during submaximal exercise below (.Q low ) and above (.Q high ) ventilatory threshold, and at each exercise stage individually (.Q exercise ). There was a significant difference between .Q baseline and all other calibration methods during exercise, but not at rest. No significant differences were observed between other methods. Closest agreement with .Q exercise was observed for .Q high (bias ± limits of agreement: 4.8 ± 30.0%). The difference between .Q exercise and both .Q low and .Q raw was characterized by low bias (4–7%) and wide limits of agreement (>±40%). Calibration of pulse contour analysis with lithium dilution prior to exercise leads to a systematic overestimation of exercising cardiac output. A single calibration performed during exercise above the ventilatory threshold provided acceptable limits of agreement with an approach incorporating multiple calibrations throughout exercise. Pulse contour analysis may be used for .Q measurement during exercise providing the system is calibrated during exercise. (paper)

  19. Maximum coherent superposition state achievement using a non-resonant pulse train in non-degenerate three-level atoms

    International Nuclear Information System (INIS)

    Deng, Li; Niu, Yueping; Jin, Luling; Gong, Shangqing

    2010-01-01

    The coherent superposition state of the lower two levels in non-degenerate three-level Λ atoms is investigated using the accumulative effects of non-resonant pulse trains when the repetition period is smaller than the decay time of the upper level. First, using a rectangular pulse train, the accumulative effects are re-examined in the non-resonant two-level atoms and the modified constructive accumulation equation is analytically given. The equation shows that the relative phase and the repetition period are important in the accumulative effect. Next, under the modified equation in the non-degenerate three-level Λ atoms, we show that besides the constructive accumulation effect, the use of the partial constructive accumulation effect can also achieve the steady state of the maximum coherent superposition state of the lower two levels and the latter condition is relatively easier to manipulate. The analysis is verified by numerical calculations. The influence of the external levels in such a case is also considered and we find that it can be avoided effectively. The above analysis is also applicable to pulse trains with arbitrary envelopes.

  20. Fast fat suppression RF pulse train with insensitivity to B1 inhomogeneity for body imaging.

    Science.gov (United States)

    Abe, Takayuki

    2012-02-01

    In higher-field magnetic resonance imaging scanners, a spectrally selective fat saturation radiofrequency (RF) pulse does not work well because B(1) inhomogeneity increases. An adiabatic 180° pulse is used to improve nonuniform fat suppression, but requires inversion recovery time. Therefore, a new RF pulse that achieves flip angles near 90° and is B(1) insensitive has been developed. The pulse consists of three sinc-shaped RF pulses with different flip angles and with different time intervals between each RF pulse. Using the Bloch equations, we analyzed the optimal combination of flip angles. Experimental results demonstrated that M(z) was maintained at less than 0.05 M(0) for a B(1) inhomogeneity of ±35%. The optimal net flip angles was adjusted to 95° by varying the time interval between RF pulses. The pulse duration was 77 ms, which is less than half of the 170-ms inversion recovery time required for the adiabatic pulse. We demonstrated excellent fat suppression for body imaging. Copyright © 2011 Wiley Periodicals, Inc.

  1. Frequency-modulated few-cycle optical-pulse-train-induced controllable ultrafast coherent population oscillations in two-level atomic systems

    Science.gov (United States)

    Kumar, Parvendra; Sarma, Amarendra K.

    2013-02-01

    We report a study on the ultrafast coherent population oscillations (UCPOs) in two-level atoms induced by a frequency-modulated few-cycle optical pulse train. The phenomenon of UCPOs is investigated by numerically solving the optical Bloch equations beyond the rotating wave approximation. We demonstrate that the quantum state of the atoms and the frequency of the UCPOs may be controlled by controlling the number of pulses in the pulse trains and the pulse repetition time, respectively. Moreover, the robustness of the population inversion against the variation of the laser pulse parameters is also investigated. The proposed scheme may be useful for the creation of atoms in selected quantum states for desired time duration and may have potential applications in ultrafast optical switching. The scheme may also be used to measure pulse repetition rate.

  2. Generation of ultrashort pulses from chromium doped cunyite laser

    Science.gov (United States)

    Jeanty, Michelet

    This thesis focuses on the generation of ultra short pulses from the chromium-doped Cunyite laser. The various principles and operation of Cunyite laser systems capable of generating femtosecond pulses in the near infrared are described. Self-starting mode-locking was successfully engineered and implemented with the assistance of semiconductor absorber mirrors (SESAMs). The broad tunability of Cr4+: Ca2GeO4 laser indicates its potential as a source of ultrafast light generation. The spectral range between 1.3 mum and 1.5mum is both important for optical communications and the eye-safe 1.45mum wavelength range. If the entire laser bandwidth of Cr4+: Ca2GeO4 are utilized, pulses as short as sub-20 fs of Cr4+: Ca2GeO 4 may be attainable. Cr4+: Ca2GeO4 laser (Cunyite) is developed at the Institute for Ultra-fast Spectroscopy and Lasers of City College of New York.The setup is formed by a standard confocal X-shaped cavity composed of the active material in the focus, and a broadband output coupler in combination with several flat mirrors used for dispersion compensation. So far, a semiconductor saturable absorber mirror (SESAM) is necessary to sustain mode-locking. Early attempts to generate mode-locked pulses led to the generation of full width at half maximum 60 picosecond pulses using an intracavity quantum-well-based semiconductor saturable absorber mirror. The SESAM is made of a thin narrow band gap absorption region, which is sandwiched between a cap layer and a spacer layer placed on the top of a high reflectivity semiconductor saturable absorber mirror. The SESAM is prepared by stacking pairs of quarter-wavelength layers that are composed of semiconductors with alternating high and low refractive indices. It consists of 24.5 periods of 123-nm AlAs low-index-104.9nm GaAs high-index quarter-wave layers for 1.43mum. The pulse width was further reduced to 8.6ps and subsequently to 365fs by using a highly-doped crystal. The tuning range of the mode-locked Cunyite

  3. Internal polarization dynamics of vector dissipative-soliton-resonance pulses in normal dispersion fiber lasers

    Science.gov (United States)

    Li, Daojing; Shen, Deyuan; Li, Lei; Tang, Dingyuan; Su, Lei; Zhao, Luming

    2018-03-01

    Investigation of internal polarization dynamics of vector dissipative-soliton-resonance (DSR) pulses in a mode-locked fiber laser is presented. Stable vector DSR pulses are experimentally ob- served. Using a waveplate-analyzer configuration, we find that polarization is not uniform across a resonant dissipative soliton. Specifically, although the central plane wave of the resonant dissi- pative soliton acquires nearly a fixed polarization, the fronts feature polarization states that are different and spatially varying. This distinct polarizaiton distribution is maintained while the whole soliton structrue extends with varying gain conditions. Numerical simulation further confirms the experimental observations.

  4. Generation of 8 nJ pulses from a normal-dispersion thulium fiber laser.

    Science.gov (United States)

    Tang, Yuxing; Chong, Andy; Wise, Frank W

    2015-05-15

    We report a study of a mode-locked thulium (Tm) fiber laser with varying normal dispersion. It is difficult to reach the high-energy dissipative-soliton regime due to the anomalous dispersion of most fibers at 2 μm. With large normal dispersion, the laser exhibits elements of self-similar pulse evolution, and is the first Tm fiber laser to achieve the performance benefits of normal-dispersion operation. The laser generates 7.6 nJ pulses, which can be dechirped to 130 fs duration. The resulting peak power is 4 times higher than that of previous Tm fiber lasers.

  5. All-optical, transform-limited and high mark-space-ratio soliton pulse train generation using both CDPF ad NOLM

    DEFF Research Database (Denmark)

    Yujun, Qian; Povlsen, Jørn Hedegård; Varming, Poul

    1999-01-01

    Soliton pulse generation from optical beat signal by both CDPF andNOLM is proposed. A transform-limited soliton train with mark-space-ratio(MSR) higher than 1:40 can be obtained at multiples of 10GHz.......Soliton pulse generation from optical beat signal by both CDPF andNOLM is proposed. A transform-limited soliton train with mark-space-ratio(MSR) higher than 1:40 can be obtained at multiples of 10GHz....

  6. The density broadening in a sodium F=2 condensate detected by a pulse train

    Directory of Open Access Journals (Sweden)

    Jianing Han

    2011-09-01

    Full Text Available The dipole-blockaded sodium clock transition has been detected by high resolution microwave spectroscopy, the multiple-pulse spectroscopy. This spectroscopic technique has been first used to detect the density broadening and shifting in a Sodium Bose Einstein Condensate (BEC by probing the sodium clock-transition. Moreover, by narrowing the pulse-width of the pulses, some of the broadening mechanisms can be partially reduced. The results reported here are essential steps toward the ground-state quantum computing, few-body spectroscopy, spin squeezing and quantum metrology.

  7. All-fiber interferometer-based repetition-rate stabilization of mode-locked lasers to 10-14-level frequency instability and 1-fs-level jitter over 1  s.

    Science.gov (United States)

    Kwon, Dohyeon; Kim, Jungwon

    2017-12-15

    We report on all-fiber Michelson interferometer-based repetition-rate stabilization of femtosecond mode-locked lasers down to 1.3×10 -14 frequency instability and 1.4 fs integrated jitter in a 1 s time scale. The use of a compactly packaged 10 km long single-mode fiber (SMF)-28 fiber link as a timing reference allows the scaling of phase noise at a 10 GHz carrier down to -80  dBc/Hz at 1 Hz Fourier frequency. We also tested a 500 m long low-thermal-sensitivity fiber as a reference and found that, compared to standard SMF-28 fiber, it can mitigate the phase noise divergence by ∼10  dB/dec in the 0.1-1 Hz Fourier frequency range. These results suggest that the use of a longer low-thermal-sensitivity fiber may achieve sub-femtosecond integrated timing jitter with sub-10 -14 -level frequency instability in repetition rate by a simple and robust all-fiber-photonic method.

  8. Simulation analysis of an improved optical triangular-shaped pulse train generator based on quadrupling RF modulation incorporating fiber dispersion-induced power fading

    Science.gov (United States)

    Li, Jing; Ning, Tigang; Pei, Li; Jian, Wei; You, Haidong; Chen, Hongyao; Li, Chao; Zhang, Chan; Ma, Shaoshuo

    2013-12-01

    We report an improved approach to generate optical triangular-shaped pulse train using quadrupling RF modulation and fiber dispersion-induced power fading. In the proposal, quadrupling RF modulation (via a dual-parallel Mach-Zehnder modulator) is employed to generate four primary optical sidebands (±2nd and ±6th) in spectrum. Then a piece of single mode fiber is connected as the dispersive media. Because of the power degradation induced by fiber dispersion, the undesired 8th order harmonic in optical intensity can be removed. It is found that when the modulation index is adjusted to a proper value (m = 4.438), optical intensity with its expression corresponding to the Fourier expansion of idea triangular-shaped waveform can be found. Since the quadrupling RF modulation technique is employed, repetition rate of the target pulse train is four times of the driving frequency, which makes pulse train generation with higher repetition rate or smaller pulse duration possible.

  9. Theory of Pulse Train Amplification Without Patterning Effects in Quantum Dot Semiconductor Optical Amplifiers

    DEFF Research Database (Denmark)

    Uskov, Alexander V.; Berg, Tommy Winther; Mørk, Jesper

    2004-01-01

    A theory for pulse amplification and saturation in quantum dot (QD) semiconductor optical amplifiers (SOAs) is developed. In particular, the maximum bit rate at which a data stream of pulses can be amplified without significant patterning effects is investigated. Simple expressions are derived th...... energies of 0.2–0.4 pJ. The superiority of QD SOAs is based on: 1) the faster achievement of the regime of maximum gain in QD SOAs compared to QW and bulk SOAs and 2) the lower effective cross section of photon-carrier interaction in QDs....

  10. Numerical evaluation of pulse-echo damage detection in train rail

    CSIR Research Space (South Africa)

    Long, CS

    2014-01-01

    Full Text Available A guided wave based monitoring system for welded freight rail, has previously been developed. The existing system was designed to only detect complete breaks. Current research efforts are focused on including a pulse-echo mode of operation in order...

  11. Limiting parameters of ultrashort pulses from a Nd-doped lanthanum-beryllate laser

    Science.gov (United States)

    Demchuk, M. I.; Mikhailov, V. P.; Gilev, A. K.; Shkadarevich, A. P.; Stavrov, A. A.

    1985-07-01

    Experiments were carried out on a Nd-doped lanthanum beryllate laser to investigate the limiting temporal and energetic parameters of ultrashort pulses and to identify the factors limiting their values. The passive mode-locking regime of the laser was investigated using a number of dyes with different nonlinear parameters. It is found that dyes 3281 and 3321 or dyes close to them in bleaching intensity and relaxation time ensure minimum duration and maximum energy of ultrashort pulses. Ultrashort pulses of 5 and 4 ps have been obtained with dyes 3228 and 3321, respectively, with the pulse energy equal to 3 mJ (pulse power of 0.75 GW) for dye 3321.

  12. Mode Locking of Quantum Cascade Lasers

    National Research Council Canada - National Science Library

    Capasso, Federico; Kaertner, Franz X

    2007-01-01

    .... A wide variety of experimental data on multimode regimes is presented. Lasers with narrow active region and/or with metal coating on the sides tend to develop a splitting in the spectrum, approximately equal to twice the Rabi frequency...

  13. The use of electric pulse training aids (EPTAs) in companion animals

    OpenAIRE

    Mills, Daniel; Soulsby, Ernest; McBride, Anne; Lamb, David; Morton, David; Wesley, Sean; Deeming, Charles; Dixon, L.; Foster, D.

    2012-01-01

    There is currently little regulation of training and behaviour modification processes in the UK (CAWC 2008) besides measures enshrined in the Animal Welfare Act 2006 and a voluntary Code of Practice launched in 2010 (see: http://www.cawc.org.uk/080603.pdf). This Code is consistent with current UK legislation outside of Wales and emphasises the need to safeguard the welfare of all interested parties involved in the “training contract” (animals and people alike) and the import...

  14. Safety training and safe operating procedures written for PBFA [Particle Beam Fusion Accelerator] II and applicable to other pulsed power facilities

    International Nuclear Information System (INIS)

    Donovan, G.L.; Goldstein, S.A.

    1986-12-01

    To ensure that work in advancing pulsed power technology is performed with an acceptably low risk, pulsed power research facilities at Sandia National Laboratories must satisfy general safety guidelines established by the Department of Energy, policies and formats of the Environment, Safety, and Health (ES and H) Department, and detailed procedures formulated by the Pulsed Power Sciences Directorate. The approach to safety training and to writing safe operating procedures, and the procedures presented here are specific to the Particle Beam Fusion Accelerator II (PBFA II) Facility but are applicable as guidelines to other research and development facilities which have similar hazards

  15. Safety training and safe operating procedures written for PBFA (Particle Beam Fusion Accelerator) II and applicable to other pulsed power facilities

    Energy Technology Data Exchange (ETDEWEB)

    Donovan, G.L.; Goldstein, S.A.

    1986-12-01

    To ensure that work in advancing pulsed power technology is performed with an acceptably low risk, pulsed power research facilities at Sandia National Laboratories must satisfy general safety guidelines established by the Department of Energy, policies and formats of the Environment, Safety, and Health (ES and H) Department, and detailed procedures formulated by the Pulsed Power Sciences Directorate. The approach to safety training and to writing safe operating procedures, and the procedures presented here are specific to the Particle Beam Fusion Accelerator II (PBFA II) Facility but are applicable as guidelines to other research and development facilities which have similar hazards.

  16. Low-cost cavity-dumped femtosecond Cr:LiSAF laser producing >100 nJ pulses.

    Science.gov (United States)

    Demirbas, Umit; Hong, Kyung-Han; Fujimoto, James G; Sennaroglu, Alphan; Kärtner, Franz X

    2010-02-15

    We report a low-cost cavity-dumped Cr:colquiriite laser for generating enhanced pulse energies. Four single-mode laser diodes were used to pump a Cr:LiSAF laser, which was mode locked with a semiconductor saturable absorber mirror. Cavity dumping at 10 kHz repetition rate, the laser generated approximately 120 fs pulses at approximately 825 nm, with 112 nJ pulse energies and approximately 0.93 MW of peak power, using only approximately 600 mW of incident pump power. At higher dumping rates of up to 1 MHz, reduced pulse energies of 62 nJ could be generated. Two-photon absorption in the saturable absorber mirror limits pulse durations, while Q-switching instabilities limit pulse energy extraction.

  17. Vector similariton erbium-doped all-fiber laser generating sub-100-fs nJ pulses at 100 MHz.

    Science.gov (United States)

    Olivier, Michel; Piché, Michel

    2016-02-08

    Erbium-doped mode-locked fiber lasers with repetition rates comparable to those of solid-state lasers and generating nJ pulses are required for many applications. Our goal was to design a fiber laser that would meet such requirements, that could be built at relatively low cost and that would be reliable and robust. We thus developed a high-fundamental-repetition-rate erbium-doped all-fiber laser operating in the amplifier similariton regime. Experimental characterization shows that this laser, which is mode-locked by nonlinear polarization evolution, emits 76-fs pulses with an energy of 1.17 nJ at a repetition rate of 100 MHz. Numerical simulations support the interpretation of self-similar evolution of the pulse in the gain fiber. More specifically we introduce the concept of vector similariton in fiber lasers. The coupled x- and y- polarization components of such a pulse have a pulse profile with a linear chirp and their combined power profile evolves self-similarly when the nonlinear asymptotic regime is reached in the gain fiber.

  18. Construction of a dog training device with high frequency and high power pulses

    International Nuclear Information System (INIS)

    Viaud Trejos, Rafael Alfonso

    2013-01-01

    An electronic device is built to produce high frequency and high power sound. The device is used in training and control of dogs. Commercial ultrasonic devices used for dog training are analyzed. The best strategies and components of the design are determined from an electronic device to produce sounds in frequency from 15kHz to 50Khz. Effectiveness tests are performed to establish the adequate design of the ultrasonic electronic device. The test results are analyzed to find opportunities of improvement in the design or construction of the device [es

  19. Six-frame picosecond radiation camera based on hydrated electron photoabsorption phenomena. [Laser opacity pattern in acidic aqueous cell formed by pulsed irradiation

    Energy Technology Data Exchange (ETDEWEB)

    Coutts, G.W.; Olk, L.B.; Gates, H.A.; St. Leger-Barter, G.

    1977-01-15

    To obtain picosecond photographs of nanosecond radiation sources, a six-frame ultra-high speed radiation camera based on hydrated electron absorption phenomena has been developed. A time-dependent opacity pattern is formed in an acidic aqueous cell by a pulsed radiation source. Six time-resolved picosecond images of this changing opacity pattern are transferred to photographic film with the use of a mode-locked dye laser and six electronically gated microchannel plate image intensifiers. Because the lifetime of the hydrated electron absorption centers can be reduced to picoseconds, the opacity patterns represent time-space pulse profile images.

  20. Pulsed laser deposition of yttria-stabilized zirconium dioxide with a high repetition rate picosecond fiber laser

    International Nuclear Information System (INIS)

    Salminen, Turkka; Hahtala, Mikko; Seppaelae, Ilkka; Niemi, Tapio; Pessa, Markus

    2010-01-01

    We report the use of a mode-locked fiber laser in pulsed laser deposition (PLD) of yttria-stabilized zirconium oxide. The fiber laser produces picosecond pulses with megahertz repetition rates at the wavelength of 1060 nm. We have investigated the effects of the time delay and the physical overlapping of the consecutive pulses on the ablation thresholds and the properties of the deposited films. Our results show existence of two distinct evaporation modes: (1) a single pulse evaporation mode observed for low overlapping and long time delays between the pulses and (2) a high repetition rate evaporation mode for high overlapping with short delays. The first mode is characterized by evaporation of nanoparticles and clusters and yields structured films with high surface area. The second mode yields smooth films, with evaporation characteristics closer to those of thermal evaporation than traditional PLD. (orig.)

  1. Impact of a web based interactive simulation game (PULSE) on nursing students' experience and performance in life support training--a pilot study.

    Science.gov (United States)

    Cook, Neal F; McAloon, Toni; O'Neill, Philip; Beggs, Richard

    2012-08-01

    The delivery of effective life support measures is highly associated with the quality, design and implementation of the education that underpins it. Effectively responding to a critical event is a requirement for all nurses illustrating the need for effective educational approaches from pre-registration training through to enhancing and maintaining life support skills after qualification. This paper reports the findings of utilising a web-based multimedia simulation game PULSE (Platform for Undergraduate Life Support Education). The platform was developed to enhance the student experience of life support education, to motivate on-going learning and engagement and to improve psychomotor skills associated with the provision of Intermediate Life Support (ILS) training. Pre training participants played PULSE and during life support training data was collected from an intervention and a control group of final year undergraduate nursing students (N=34). Quantitative analysis of performance took place and qualitative data was generated from a questionnaire assessing the learning experience. A statistically significant difference was found between the competence the groups displayed in the three skills sets of checking equipment, airway assessment and the safe/effective use of defibrillator at ILS level, and PULSE was positively evaluated as an educational tool when used alongside traditional life support training. Copyright © 2011 Elsevier Ltd. All rights reserved.

  2. Dual-scale nanoripple/nanoparticle-covered microspikes on silicon by femtosecond double pulse train irradiation in water

    Energy Technology Data Exchange (ETDEWEB)

    Meng, Ge; Jiang, Lan [Laser Micro/Nano Fabrication Laboratory, School of Mechanical Engineering, Beijing Institute of Technology, Beijing 100081 (China); Li, Xin, E-mail: lixin02@bit.edu.cn [Laser Micro/Nano Fabrication Laboratory, School of Mechanical Engineering, Beijing Institute of Technology, Beijing 100081 (China); Xu, Yongda; Shi, Xuesong; Yan, Ruyu [Laser Micro/Nano Fabrication Laboratory, School of Mechanical Engineering, Beijing Institute of Technology, Beijing 100081 (China); Lu, Yongfeng [Department of Electrical Engineering, University of Nebraska-Lincoln, Lincoln, NE 68588-0511 (United States)

    2017-07-15

    Highlights: • A simple method to fabricate dual-scale structures on silicon is proposed. • Nanoripple-covered or nanoparticle-covered microspikes are obtained on Si firstly. • They are obtained by temporally-shaped fs laser one-step irradiation in water. • Their application in SERS was proved with a high sensitivity of up to 10{sup 8}. - Abstract: Novel dual-scale structures were obtained by femtosecond double pulse train (subpulse delay Δt > 0 ps) one-step irradiating silicon in water. The dual-scale structures consist of microspikes of ∼2 μm width and ∼0.5 μm height, and nanoripples with a mean period of 146 nm or nanoparticles with a mean diameter of 90 nm which entirely cover on the microspikes, for linearly polarized or circularly polarized femtosecond laser respectively. The formation of dual-scale structures involves the following processes: (1) Continuously laser energy deposited at femtosecond to picosecond timescales within silicon surfaces and central regions, will result in enhanced capillary waves and thinner melted silicon layers. Hence, the microspikes can be induced at laser fluences below ablation threshold; (2) Later (>500–800 pulses), a mass of debris and bubbles produced will lead to the remarkably and uniformly scattering or shielding of subsequent incident laser energy. Hence, the nanostructures can be induced. The novel structures exhibit high-sensitive surface enhanced Raman scattering with an enhancement factor of 10{sup 8} for Rhodamine 6G detecting. Besides, the novel structures have application potentials in improving the silicon hydrophobicity, antireflection, etc.

  3. Dual-scale nanoripple/nanoparticle-covered microspikes on silicon by femtosecond double pulse train irradiation in water

    International Nuclear Information System (INIS)

    Meng, Ge; Jiang, Lan; Li, Xin; Xu, Yongda; Shi, Xuesong; Yan, Ruyu; Lu, Yongfeng

    2017-01-01

    Highlights: • A simple method to fabricate dual-scale structures on silicon is proposed. • Nanoripple-covered or nanoparticle-covered microspikes are obtained on Si firstly. • They are obtained by temporally-shaped fs laser one-step irradiation in water. • Their application in SERS was proved with a high sensitivity of up to 10 8 . - Abstract: Novel dual-scale structures were obtained by femtosecond double pulse train (subpulse delay Δt > 0 ps) one-step irradiating silicon in water. The dual-scale structures consist of microspikes of ∼2 μm width and ∼0.5 μm height, and nanoripples with a mean period of 146 nm or nanoparticles with a mean diameter of 90 nm which entirely cover on the microspikes, for linearly polarized or circularly polarized femtosecond laser respectively. The formation of dual-scale structures involves the following processes: (1) Continuously laser energy deposited at femtosecond to picosecond timescales within silicon surfaces and central regions, will result in enhanced capillary waves and thinner melted silicon layers. Hence, the microspikes can be induced at laser fluences below ablation threshold; (2) Later (>500–800 pulses), a mass of debris and bubbles produced will lead to the remarkably and uniformly scattering or shielding of subsequent incident laser energy. Hence, the nanostructures can be induced. The novel structures exhibit high-sensitive surface enhanced Raman scattering with an enhancement factor of 10 8 for Rhodamine 6G detecting. Besides, the novel structures have application potentials in improving the silicon hydrophobicity, antireflection, etc.

  4. Fast amplitude-modulated pulse trains with frequency sweep (SW-FAM) in static NMR of half-integer spin quadrupolar nuclei.

    Science.gov (United States)

    Bräuniger, Thomas; Hempel, Günter; Madhu, P K

    2006-07-01

    In solid-state NMR of quadrupolar nuclei with half-integer spin I, fast amplitude-modulated (FAM) pulse trains have been utilised to enhance the intensity of the central-transition signal, by transferring spin population from the satellite transitions. In this paper, the signal-enhancement performance of the recently introduced SW-FAM pulse train with swept modulation frequency [T. Bräuniger, K. Ramaswamy, P.K. Madhu, Enhancement of the central-transition signal in static and magic-angle-spinning NMR of quadrupolar nuclei by frequency-swept fast amplitude-modulated pulses, Chem. Phys. Lett. 383 (2004) 403-410] is explored in more detail for static spectra. It is shown that by sweeping the modulation frequencies linearly over the pulse pairs (SW1/tau-FAM), the shape of the frequency distribution is improved in comparison to the original pulse scheme (SWtau-FAM). For static spectra of 27Al (I=5/2), better signal-enhancement performance is found for the SW1/tau-FAM sequence, as demonstrated both by experiments and numerical simulations.

  5. Large-area highly crystalline WSe2atomic layers for ultrafast pulsed lasers.

    Science.gov (United States)

    Yin, Jinde; Li, Jiarong; Chen, Hao; Wang, Jintao; Yan, Peiguang; Liu, Mengli; Liu, Wenjun; Lu, Wei; Xu, Zihan; Zhang, Wenfei; Wang, Jinzhang; Sun, Zhipei; Ruan, Shuangchen

    2017-11-27

    Large-area and highly crystalline transition metal dichalcogenides (TMDs) films possess superior saturable absorption compared to the TMDs nanosheet counterparts, which make them more suitable as excellent saturable absorbers (SA) for ultrafast laser technology. Thus far, the nonlinear optical properties of large-scale WSe 2 and its applications in ultrafast photonics have not yet been fully investigated. In this work, the saturable absorption of chemical vapor deposition (CVD) grown WSe 2 films with large-scale and high quality are studied and the use of WSe 2 films as a broadband SA for passively mode-locked fiber lasers at both 1.5 and 2 μm ranges is demonstrated. To enhance the light-material interaction, large-area WSe 2 film is tightly transferred onto the side wall of a microfiber to form a hybrid structure, which realizes strong evanescent wave interaction between light and WSe 2 film. The integrated microfiber-WSe 2 device shows a large modulation depth of 54.5%. Using the large-area WSe 2 as a mode-locker, stable soliton mode-locked pulse generation is achieved and the pulse durations of 477 fs (at 1.5 μm) and 1.18 ps (at 2.0 μm) are demonstrated, which suggests that the large-area and highly crystalline WSe 2 films afford an excellent broadband SA for ultrafast photonic applications.

  6. Simultaneously Excitatory and Inhibitory Effects of Transcranial Alternating Current Stimulation Revealed Using Selective Pulse-Train Stimulation in the Rat Motor Cortex.

    Science.gov (United States)

    Khatoun, Ahmad; Asamoah, Boateng; Mc Laughlin, Myles

    2017-09-27

    Transcranial alternating current stimulation (tACS) uses sinusoidal, subthreshold, electric fields to modulate cortical processing. Cortical processing depends on a fine balance between excitation and inhibition and tACS acts on both excitatory and inhibitory cortical neurons. Given this, it is not clear whether tACS should increase or decrease cortical excitability. We investigated this using transcranial current stimulation of the rat (all males) motor cortex consisting of a continuous subthreshold sine wave with short bursts of suprathreshold pulse-trains inserted at different phases to probe cortical excitability. We found that when a low-rate, long-duration, suprathreshold pulse-train was used, subthreshold cathodal tACS decreased cortical excitability and anodal tACS increased excitability. However, when a high-rate, short-duration, suprathreshold pulse-train was used this pattern was inverted. An integrate-and-fire model incorporating biophysical differences between cortical excitatory and inhibitory neurons could predict the experimental data and helped interpret these results. The model indicated that low-rate suprathreshold pulse-trains preferentially stimulate excitatory cortical neurons, whereas high-rate suprathreshold pulse-trains stimulate both excitatory and inhibitory neurons. If correct, this indicates that suprathreshold pulse-train stimulation may be able to selectively control the excitation-inhibition balance within a cortical network. The excitation-inhibition balance then likely plays an important role in determining whether subthreshold tACS will increase or decrease cortical excitability. SIGNIFICANCE STATEMENT Transcranial alternating current stimulation (tACS) is a noninvasive neuromodulation method that uses weak sinusoidal electric fields to modulate cortical activity. In healthy volunteers tACS can modulate perception, cognition, and motor function but the underlying neural mechanism is poorly understood. In this study, using rat

  7. Gating circuit for single photon-counting fluorescence lifetime instruments using high repetition pulsed light sources

    International Nuclear Information System (INIS)

    Laws, W.R.; Potter, D.W.; Sutherland, J.C.

    1984-01-01

    We have constructed a circuit that permits conventional timing electronics to be used in single photon-counting fluorimeters with high repetition rate excitation sources (synchrotrons and mode-locked lasers). Most commercial time-to-amplitude and time-to-digital converters introduce errors when processing very short time intervals and when subjected to high-frequency signals. This circuit reduces the frequency of signals representing the pulsed light source (stops) to the rate of detected fluorescence events (starts). Precise timing between the start/stop pair is accomplished by using the second stop pulse after a start pulse. Important features of our design are that the circuit is insensitive to the simultaneous occurrence of start and stop signals and that the reduction in the stop frequency allows the start/stop time interval to be placed in linear regions of the response functions of commercial timing electronics

  8. 1-MHz high power femtosecond Yb-doped fiber chirped-pulse amplifier

    Science.gov (United States)

    Hu, Zhong-Qi; Yang, Pei-Long; Teng, Hao; Zhu, Jiang-Feng; Wei, Zhi-Yi

    2018-01-01

    A practical femtosecond polarization-maintaining Yb-doped fiber amplifier enabling 153 fs transform-limited pulse duration with 32 μJ pulse energy at 1 MHz repetition rate corresponding to a peak power of 0.21 GW is demonstrated. The laser system based on chirped-pulse amplification (CPA) technique is seeded by a dispersion managed, nonlinear polarization evolution (NPE) mode-locked oscillator with spectrum bandwidth of 31 nm at 1040 nm and amplified by three fiber pre-amplifying stages and a rod type fiber main amplifying stage. The laser works with beam quality of M2 of 1.3 and power stability of 0.63% (root mean square, RMS) over 24 hours will be stable sources for industrial micromachining, medical therapy and scientific research.

  9. Pulsed-diode-pumped, all-solid-state, electro-optically controlled picosecond Nd:YAG lasers

    International Nuclear Information System (INIS)

    Gorbunkov, Mikhail V; Shabalin, Yu V; Konyashkin, A V; Kostryukov, P V; Olenin, A N; Tunkin, V G; Morozov, V B; Rusov, V A; Telegin, L S; Yakovlev, D V

    2005-01-01

    The results of the development of repetitively pulsed, diode-pumped, electro-optically controlled picosecond Nd:YAG lasers of two designs are presented. The first design uses the active-passive mode locking with electro-optical lasing control and semiconductor saturable absorber mirrors (SESAM). This design allows the generation of 15-50-ps pulses with an energy up to 0.5 mJ and a maximum pulse repetition rate of 100 Hz. The laser of the second design generates 30-ps pulses due to combination of positive and negative electro-optical feedback and the control of the electro-optical modulator by the photocurrent of high-speed semiconductor structures. (active media. lasers)

  10. Lifetime measurement of the cesium 6P3/2 state using ultrafast laser-pulse excitation and ionization

    International Nuclear Information System (INIS)

    Sell, J. F.; Patterson, B. M.; Ehrenreich, T.; Brooke, G.; Scoville, J.; Knize, R. J.

    2011-01-01

    We report a precision measurement of the cesium 6P 3/2 excited-state lifetime. Two collimated, counterpropagating thermal Cs beams cross perpendicularly to femtosecond pulsed laser beams. High timing accuracy is achieved from having excitation and ionization laser pulses which originate from the same mode-locked laser. Using pulse selection we vary the separation in time between excitation and ionization laser pulses while counting the ions produced. We obtain a Cs 6P 3/2 lifetime of 30.460(38) ns, which is a factor of two improvement from previous measurements and with an uncertainty of 0.12%, is one of the most accurate lifetime measurements on record.

  11. Testing of a femtosecond pulse laser in outer space.

    Science.gov (United States)

    Lee, Joohyung; Lee, Keunwoo; Jang, Yoon-Soo; Jang, Heesuk; Han, Seongheum; Lee, Sang-Hyun; Kang, Kyung-In; Lim, Chul-Woo; Kim, Young-Jin; Kim, Seung-Woo

    2014-05-30

    We report a test operation of an Er-doped fibre femtosecond laser which was conducted for the first time in outer space. The fibre-based ultrashort pulse laser payload was designed to meet space-use requirements, undergone through ground qualification tests and finally launched into a low-earth orbit early in 2013. Test results obtained during a one-year mission lifetime confirmed stable mode-locking all the way through although the radiation induced attenuation (RIA) in the Er-doped gain fibre caused an 8.6% reduction in the output power. This successful test operation would help facilitate diverse scientific and technological applications of femtosecond lasers in space and earth atmosphere in the near future.

  12. Testing of a femtosecond pulse laser in outer space

    Science.gov (United States)

    Lee, Joohyung; Lee, Keunwoo; Jang, Yoon-Soo; Jang, Heesuk; Han, Seongheum; Lee, Sang-Hyun; Kang, Kyung-In; Lim, Chul-Woo; Kim, Young-Jin; Kim, Seung-Woo

    2014-01-01

    We report a test operation of an Er-doped fibre femtosecond laser which was conducted for the first time in outer space. The fibre-based ultrashort pulse laser payload was designed to meet space-use requirements, undergone through ground qualification tests and finally launched into a low-earth orbit early in 2013. Test results obtained during a one-year mission lifetime confirmed stable mode-locking all the way through although the radiation induced attenuation (RIA) in the Er-doped gain fibre caused an 8.6% reduction in the output power. This successful test operation would help facilitate diverse scientific and technological applications of femtosecond lasers in space and earth atmosphere in the near future. PMID:24875665

  13. Repetition-rate-tunable return-to-zero and carrier-suppressed return-to-zero optical pulse train generation using a polarization modulator.

    Science.gov (United States)

    Zou, Xihua; Yao, Jianping

    2009-02-01

    An approach is proposed to generating return-to-zero (RZ) and carrier-suppressed return-to-zero (CS-RZ) pulse trains with a high and tunable repetition rate by using a polarization modulator (PolM). The PolM is a special phase modulator that can support both TE and TM modes with opposite phase modulation indices. A linearly polarized cw light with its polarization state oriented with an angle of 45 degrees to one principal axis of the PolM is modulated by a sinusoidal signal at the PolM. The output light from the PolM is then sent to a polarization beam splitter (PBS), with one axis of the PBS aligned at an angle of 45 degrees to one principle axis of the PolM. At the two outputs of the PBS, two optical signals with one consisting of the even-order optical sidebands and the other consisting of the odd-order optical sidebands are obtained, leading to the generation of an RZ and a CS-RZ pulse train having a repetition rate that is twice the frequency of the drive sinusoidal signal. The proposed approach is demonstrated by a proof-of-concept experiment in which an RZ and a CS-RZ pulse train with tunable repetition rates of 7.2 and 8 GHz are generated.

  14. Effect of intradialytic resistance training on pulse wave velocity and associated cardiovascular disease biomarkers in end stage renal disease.

    Science.gov (United States)

    Chan, Danwin; Green, Simon; Fiatarone Singh, Maria A; Barnard, Robert; Bonder, Claudine S; Cheema, Birinder S

    2017-12-19

    Cardiovascular disease (CVD) is the leading cause of mortality in patients with end-stage renal disease (ESRD) receiving maintenance hemodialysis treatment. This study investigated the effect of a 12-week intradialytic progressive resistance training (PRT) intervention on pulse wave velocity (PWV) and associated hemodynamic, anthropometric, and hematologic outcomes in patients with ESRD. Twenty-two patients with ESRD (59% men, 71.3 ± 11.0 years) were recruited. Supervised PRT (3 sets of 11 exercises) was prescribed three times per week during routine dialysis. The primary outcome was brachial-ankle PWV via applanation tonometry. Secondary outcomes included augmentation index, brachial and aortic blood pressures, endothelial progenitor cells, C-reactive protein, blood lipids and anthropometrics. The intradialytic PRT regimen resulted in no significant change in PWV between control and intervention periods [mean difference = 0 (95% CI = -0.1 to 0.1); P=0.58]. Similarly, no significant change was noted in any secondary outcome measures between the control and intervention periods. Post-hoc analyses limited to high adherers (≥75% attendance; n=11) did not differ from the primary analysis, indicating no dose-response effect of our intervention. Our 12-week PRT intervention did not change PWV or any secondary outcomes. Future studies should determine if higher dosages of intradialytic PRT (i.e. longer duration and/or higher intensity) can be applied as a method improve arterial stiffness to potentially reduce cardiovascular disease and associated mortality this cohort. This article is protected by copyright. All rights reserved.

  15. Effects of short-term resistance training and pulsed electromagnetic fields on bone metabolism and joint function in severe haemophilia A patients with osteoporosis: a randomized controlled trial.

    Science.gov (United States)

    Parhampour, Behrouz; Torkaman, Giti; Hoorfar, Hamid; Hedayati, Mehdi; Ravanbod, Roya

    2014-05-01

    To assess the effects of short-term resistance training and pulsed electromagnetic fields on bone metabolism and joint function in patients with haemophilia with osteoporosis. A randomized, controlled, patient and blood sample assessor-blinded, six-week trial, three times weekly. Hospital outpatients with severe haemophilia A and osteoporosis. Forty-eight patients were randomly assigned to resistance training (RT, n = 13), combined resistance training with pulsed electromagnetic fields (RTPEMF, n = 12), pulsed electromagnetic fields (PEMF, n = 11) and control (n = 12) groups. The RT group received 30-40 minutes of resistance exercises and placebo pulsed electromagnetic fields. The RTPEMF group received the same exercises with lower repetition and 30 minutes of pulsed electromagnetic fields. The PEMF group was exposed to 60 minutes of pulsed electromagnetic fields (30 Hz and 40 Gauss). Bone-specific alkaline phosphatase, N-terminal telopeptide of type 1 collagen, and joint function, using the modified Colorado Questionnaire, were measured before and after the programme. The absolute change of bone-specific alkaline phosphatase was significant in the RT and RTPEMF groups compared with the control group (25.41 ± 14.40, 15.09 ± 5.51, and -4.73 ± 2.93 U/L, respectively). The absolute changes in the total score for joint function were significant for knees, ankles, and elbows in the RT group (9.2 ± 1.38, 5.1 ± 0.5, and 3.2 ± 0.8, respectively) and the RTPEMF group (7.7 ± 1.0, 3.3 ± 0.6, and 2.5 ± 0.7, respectively) compared to the PEMF and control groups. This value was significant for knee joints in the PEMF group compared to the control group (3.4 ± 0.5 and 0.66 ± 0.4, respectively). Resistance training is effective for improving bone formation and joint function in severe haemophilia A patients with osteoporosis.

  16. Pulse plating

    CERN Document Server

    Hansal, Wolfgang E G; Green, Todd; Leisner, Peter; Reichenbach, Andreas

    2012-01-01

    The electrodeposition of metals using pulsed current has achieved practical importance in recent years. Although it has long been known that changes in potential, with or without polarity reversal, can significantly affect the deposition process, the practical application of this has been slow to be adopted. This can largely be explained in terms of the complex relationship between the current regime and its effect on the electrodeposition process. In order to harness these effects, an understanding of the anodic and cathodic electrochemical processes is necessary, together with the effects of polarity reversal and the rate of such reversals. In this new monograph, the basics of metal electrodeposition from solution are laid out in great detail in seven distinct chapters. With this knowledge, the reader is able to predict how a given pulse train profile can be adopted to achieve a desired outcome. Equally important is the choice of a suitable rectifier and the ancillary control circuits to enable pulse platin...

  17. Building Of Training Program Of Non-Destructive Testing For Concrete Structures (Part 1: Radiographic testing; Ultrasonic pulse velocity measurement; Nuclear moisture-density gauge)

    International Nuclear Information System (INIS)

    Nguyen Le Son; Phan Chanh Vu; Pham The Hung; Vu Huy Thuc

    2007-01-01

    Non-destructive testing methods (NDT) have been identified as a strong candidate for remote sensing of concrete structures over recent years. This has accelerated the powerful development of the NDT techniques in Vietnam. Hence, there is an urgent need to promote the awareness of NDT methods which could give an improved estimate of the condition concrete. Building of training program of non-destructive testing for concrete structures is a necessary duty, in aiming to build a unified training program, possibly satisfying the requirements on training as well as researching. Under the framework of the basic VAEC project (CS/07/02-03), a training program for the first 03 NDT methods: 1. Radiographic testing; 2. Ultrasonic pulse velocity measurement; 3. Nuclear moisture- density gauge was prepared. The main products of this project include: 1. Set out 03 training notes for 03 methods; 2. Set out the practical exercises to train for 03 methods; 3. Editing a set of examination questions in aiming to familiarize with various questions in 03 trained methods; 4. Fabricating practical test specimens to demonstrate for 03 techniques. (author)

  18. Multi-channel, fiber-based seed pulse distribution system for femtosecond-level synchronized chirped pulse amplifiers.

    Science.gov (United States)

    Horáček, Martin; Indra, Lukáš; Green, Jonathan T; Naylon, Jack A; Tykalewicz, Boguslaw; Novák, Jakub; Batysta, František; Mazanec, Tomáš; Horáček, Jakub; Antipenkov, Roman; Hubka, Zbyněk; Boge, Robert; Bakule, Pavel; Rus, Bedřich

    2017-01-01

    We report on the design and performance of a fiber-based, multi-channel laser amplifier seed pulse distribution system. The device is designed to condition and distribute low energy laser pulses from a mode-locked oscillator to multiple, highly synchronized, high energy amplifiers integrated into a laser beamline. Critical functions such as temporal pulse stretching well beyond 100 ps/nm, pulse picking, and fine control over the pulse delay up to 300 ps are all performed in fiber eliminating the need for bulky and expensive grating stretchers, Pockels cells, and delay lines. These functions are characterized and the system as a whole is demonstrated by seeding two high energy amplifiers in the laser beamline. The design of this system allows for complete computer control of all functions, including tuning of dispersion, and is entirely hands-free. The performance of this device and its subsystems will be relevant to those developing lasers where reliability, size, and cost are key concerns in addition to performance; this includes those developing large-scale laser systems similar to ours and also those developing table-top experiments and commercial systems.

  19. Evolution of Hyperbolic-Secant Pulses Towards Cross-Phase Modulation Induced Optical Wave Breaking and Soliton or Soliton Trains Generation in Quintic Nonlinear Fibers

    Science.gov (United States)

    Zhong, Xian-Qiong; Zhang, Xiao-Xia; Du, Xian-Tong; Liu, Yong; Cheng, Ke

    2015-10-01

    The approximate analytical frequency chirps and the critical distances for cross-phase modulation induced optical wave breaking (OWB) of the initial hyperbolic-secant optical pulses propagating in optical fibers with quintic nonlinearity (QN) are presented. The pulse evolutions in terms of the frequency chirps, shapes and spectra are numerically calculated in the normal dispersion regime. The results reveal that, depending on different QN parameters, the traditional OWB or soliton or soliton pulse trains may occur. The approximate analytical critical distances are found to be in good agreement with the numerical ones only for the traditional OWB whereas the approximate analytical frequency chirps accords well with the numerical ones at the initial evolution stages of the pulses. Supported by the Postdoctoral Fund of China under Grant No. 2011M501402, the Key Project of Chinese Ministry of Education under Grant No. 210186, the Major Project of Natural Science Supported by the Educational Department of Sichuan Province under Grant No. 13ZA0081, the Key Project of National Natural Science Foundation of China under Grant No 61435010, and the National Natural Science Foundation of China under Grant No. 61275039

  20. Soliton formation from a noise-like pulse during extreme events in a fibre ring laser

    Science.gov (United States)

    Pottiez, O.; Ibarra-Villalon, H. E.; Bracamontes-Rodriguez, Y.; Minguela-Gallardo, J. A.; Garcia-Sanchez, E.; Lauterio-Cruz, J. P.; Hernandez-Garcia, J. C.; Bello-Jimenez, M.; Kuzin, E. A.

    2017-10-01

    We study experimentally the interactions between soliton and noise-like pulse (NLP) components in a mode-locked fibre ring laser operating in a hybrid soliton-NLP regime. For proper polarization adjustments, one NLP and multiple packets of solitons coexist in the cavity, at 1530 nm and 1558 nm, respectively. By examining time-domain sequences measured using a 16 GHz real-time oscilloscope, we unveil the process of soliton genesis: they are produced during extreme-intensity episodes affecting the NLP. These extreme events can emerge sporadically, appear in small groups or even form quasi-periodic sequences. Once formed, the wavelength-shifted soliton packet drifts away from the NLP in the dispersive cavity, and eventually vanishes after a variable lifetime. Evidence of the inverse process, through which NLP formation is occasionally seeded by an extreme-intensity event affecting a bunch of solitons, is also provided. The quasi-stationary dynamics described here constitutes an impressive illustration of the connections and interactions between NLPs, extreme events and solitons in passively mode-locked fibre lasers.

  1. Towards ‘smart lasers’: self-optimisation of an ultrafast pulse source using a genetic algorithm

    Science.gov (United States)

    Woodward, R. I.; Kelleher, E. J. R.

    2016-11-01

    Short-pulse fibre lasers are a complex dynamical system possessing a broad space of operating states that can be accessed through control of cavity parameters. Determination of target regimes is a multi-parameter global optimisation problem. Here, we report the implementation of a genetic algorithm to intelligently locate optimum parameters for stable single-pulse mode- locking in a Figure-8 fibre laser, and fully automate the system turn-on procedure. Stable ultrashort pulses are repeatably achieved by employing a compound fitness function that monitors both temporal and spectral output properties of the laser. Our method of encoding photonics expertise into an algorithm and applying machine-learning principles paves the way to self-optimising ‘smart’ optical technologies.

  2. Compression of 200 GHz DWDM channelized TDM pulsed carrier from optically modelocking WRC-FPLD fiber ring at 10 GHz.

    Science.gov (United States)

    Lin, Yu-Chan; Peng, Guo-Hsuan; Lin, Gong-Ru

    2009-03-30

    The compression of 200GHz DWDM channelized optically mode-locking WRC-FPLD fiber ring pulse of at 10 GHz is performed for high-capacity TDM application. To prevent temporal and spectral cross-talk, the duty-cycle of the DWDM channelized WRC-FPLD FL pulse needs to be shortened without broadening its linewidth. With dual-cavity configuration induced DWDM channelization, a shortest single-channel WRC-FPLD FL pulsewidth of 19 ps is generated, which can be linearly compensated to 10 ps and fifth-order soliton compressed to 1.4 ps. Under a maximum pulsewidth compression ratio up to 14 and a +/-100 m tolerance on compressing fiber length, the single-channel pulsewidth remains DWDM channelized WRC-FPLD FL pulsed carrier is approaching 1% to satisfy at least 256 optical TDM channels.

  3. Molecular orientation via a dynamically induced pulse-train: Wave packet dynamics of NaI in a static electric field

    DEFF Research Database (Denmark)

    Marquetand, P.; Materny, A.; Henriksen, Niels Engholm

    2004-01-01

    We regard the rovibrational wave packet dynamics of NaI in a static electric field after femtosecond excitation to its first electronically excited state. The following quasibound nuclear wave packet motion is accompanied by a bonding situation changing from covalent to ionic. At times when...... the charge separation is present, i.e., when the bond-length is large, a strong dipole moment exists and rotational excitation takes place. Upon bond contraction, the then covalently bound molecule does not experience the external field. This scenario repeats itself periodically. Thus, the vibrational...... dynamics causes a situation which is comparable to the interaction of the molecule with a train of pulses where the pulse separation is determined by the vibrational period. (C) 2004 American Institute of Physics....

  4. Source of ultra-short laser pulses at 1,55μm in vertical-external-cavity for linear optical sampling applications

    International Nuclear Information System (INIS)

    Khadour, A.

    2009-12-01

    The objectives of this thesis were, in a first step, to develop and implement VECSEL structures containing an active zone formed by GaAlInAs/InP quantum wells located at the anti-nodes of the resonant electric field, positioned on a Bragg mirror, all this being bonded to a substrate of good thermal conductivity. For this, we have designed structures optimizing the evacuation of heat generated in the active zone. This has greatly improved the VECSEL performances, especially their output power. The VECSEL performances were evaluated in a simple cavity with two mirrors (plane-concave). The second point was to develop and implement SESAM structures which, owing to their nonlinear characteristics, would allow a passively mode-locked laser operation. The structures contained InGaAsN/GaAs quantum wells. The studied parameters were the number of quantum wells, and the resonant or anti-resonant behavior of the structure. The linear and nonlinear optical characterizations were used to optimize the SESAM structure and estimate their performances. Finally, the compatibility between the VECSEL and SESAM structures, in terms of modulation depth and resonance wavelength, made it possible to obtain the passive mode locking operation. The obtained pulses show two different behaviors depending on the dispersion properties of the structures. With low dispersion, we have made the first demonstration of a passively mode-locked VECSEL at 1550 nm, operating at room temperature. An all-optical sampling device implementing the linear optical sampling technique using short laser pulses has been realized and tested. This device will allow displaying eye diagrams and constellation diagrams with an expected sensitivity around -20 dBm of average power. Testing the device allowed to visualize the acquisition of very high repetition rate signals (40 Gb/s). (author)

  5. Bandwidth and repetition rate programmable Nyquist sinc-shaped pulse train source based on intensity modulators and four-wave mixing.

    Science.gov (United States)

    Cordette, S; Vedadi, A; Shoaie, M A; Brès, C-S

    2014-12-01

    We propose and experimentally demonstrate an all-optical Nyquist sinc-shaped pulse train source based on intensity modulation and four-wave mixing. The proposed scheme allows for the tunability of the bandwidth and the full flexibility of the repetition rate in the limit of the electronic bandwidth of the modulators used through the flexible synthesis of rectangular frequency combs. Bandwidth up to 360 GHz at 40 GHz rate and up to 45 frequency lines at 5 GHz rate are demonstrated with 40 GHz modulators.

  6. Pulse!!: a model for research and development of virtual-reality learning in military medical education and training.

    Science.gov (United States)

    Dunne, James R; McDonald, Claudia L

    2010-07-01

    Pulse!! The Virtual Clinical Learning Lab at Texas A&M University-Corpus Christi, in collaboration with the United States Navy, has developed a model for research and technological development that they believe is an essential element in the future of military and civilian medical education. The Pulse!! project models a strategy for providing cross-disciplinary expertise and resources to educational, governmental, and business entities challenged with meeting looming health care crises. It includes a three-dimensional virtual learning platform that provides unlimited, repeatable, immersive clinical experiences without risk to patients, and is available anywhere there is a computer. Pulse!! utilizes expertise in the fields of medicine, medical education, computer science, software engineering, physics, computer animation, art, and architecture. Lab scientists collaborate with the commercial virtual-reality simulation industry to produce research-based learning platforms based on cutting-edge computer technology.

  7. Generation of spin waves by a train of fs-laser pulses: a novel approach for tuning magnon wavelength.

    Science.gov (United States)

    Savochkin, I V; Jäckl, M; Belotelov, V I; Akimov, I A; Kozhaev, M A; Sylgacheva, D A; Chernov, A I; Shaposhnikov, A N; Prokopov, A R; Berzhansky, V N; Yakovlev, D R; Zvezdin, A K; Bayer, M

    2017-07-18

    Currently spin waves are considered for computation and data processing as an alternative to charge currents. Generation of spin waves by ultrashort laser pulses provides several important advances with respect to conventional approaches using microwaves. In particular, focused laser spot works as a point source for spin waves and allows for directional control of spin waves and switching between their different types. For further progress in this direction it is important to manipulate with the spectrum of the optically generated spin waves. Here we tackle this problem by launching spin waves by a sequence of femtosecond laser pulses with pulse interval much shorter than the relaxation time of the magnetization oscillations. This leads to the cumulative phenomenon and allows us to generate magnons in a specific narrow range of wavenumbers. The wavelength of spin waves can be tuned from 15 μm to hundreds of microns by sweeping the external magnetic field by only 10 Oe or by slight variation of the pulse repetition rate. Our findings expand the capabilities of the optical spin pump-probe technique and provide a new method for the spin wave generation and control.

  8. Verbal attribute magnitude estimates of pulse trains acros selectrode places and stimulation rates in cochlear implant listeners

    DEFF Research Database (Denmark)

    Lamping, Wiebke; Santurette, Sébastien; Marozeau, Jeremy

    2017-01-01

    For cochlear implant users, temporal and place cue are assumed to varyalong two orthogonal perceptual dimensions linked to pitch height and timbre.Here, the effect of electrode place, pulse rate, and amplitude modulationfrequency on those perceptual dimensions was investigated. Combinations ofdif...

  9. Extension of supercontinuum spectrum generated in photonic crystal fiber by using chirped femtosecond pulses

    Science.gov (United States)

    Vengelis, Julius; Jarutis, Vygandas; Sirutkaitis, Valdas

    2017-08-01

    We present results of experimental and numerical investigation of supercontinuum generation in polarization maintaining photonic crystal fiber (PCF) using chirped femtosecond pulses. The initial unchirped pump pulse source was a mode-locked Yb:KGW laser generating 52 nJ energy 110 fs duration pulses at 1030 nm with 76 MHz repetition rate. The nonlinear medium was a 32 cm long polarization maintaining PCF manufactured by NKT Photonics A/S. We demonstrated the influence of pump pulse chirp on spectral characteristics of supercontinuum. We showed that by chirping pump pulses positively or negatively one can obtain broader supercontinuum spectrum than in case of unchirped pump pulses at the same peak power. Moreover, the extension can be controlled by changing the amount of pump pulse chirp. In our case the supercontinuum spectrum width was extended by up to 115 nm (at maximum chirp value of +10500 fs2 that we could achieve in our setup) compared to the case of unchirped pump at the same peak power.

  10. Generation of spin waves by a train of fs-laser pulses: a novel approach for tuning magnon wavelength

    OpenAIRE

    Savochkin, I. V.; J?ckl, M.; Belotelov, V. I.; Akimov, I. A.; Kozhaev, M. A.; Sylgacheva, D. A.; Chernov, A. I.; Shaposhnikov, A. N.; Prokopov, A. R.; Berzhansky, V. N.; Yakovlev, D. R.; Zvezdin, A. K.; Bayer, M.

    2017-01-01

    Currently spin waves are considered for computation and data processing as an alternative to charge currents. Generation of spin waves by ultrashort laser pulses provides several important advances with respect to conventional approaches using microwaves. In particular, focused laser spot works as a point source for spin waves and allows for directional control of spin waves and switching between their different types. For further progress in this direction it is important to manipulate with ...

  11. Synchronization System for Next Generation Light Sources

    Energy Technology Data Exchange (ETDEWEB)

    Zavriyev, Anton [MagiQ Technologies, Inc., Somerville, MA (United States)

    2014-03-27

    An alternative synchronization technique – one that would allow explicit control of the pulse train including its repetition rate and delay is clearly desired. We propose such a scheme. Our method is based on optical interferometry and permits synchronization of the pulse trains generated by two independent mode-locked lasers. As the next generation x-ray sources will be driven by a clock signal derived from a mode-locked optical source, our technique will provide a way to synchronize x-ray probe with the optical pump pulses.

  12. Variable delay multi-pulse train for fast chemical exchange saturation transfer and relayed-nuclear overhauser enhancement MRI.

    Science.gov (United States)

    Xu, Jiadi; Yadav, Nirbhay N; Bar-Shir, Amnon; Jones, Craig K; Chan, Kannie W Y; Zhang, Jiangyang; Walczak, P; McMahon, Michael T; van Zijl, Peter C M

    2014-05-01

    Chemical exchange saturation transfer (CEST) imaging is a new MRI technology allowing the detection of low concentration endogenous cellular proteins and metabolites indirectly through their exchangeable protons. A new technique, variable delay multi-pulse CEST (VDMP-CEST), is proposed to eliminate the need for recording full Z-spectra and performing asymmetry analysis to obtain CEST contrast. The VDMP-CEST scheme involves acquiring images with two (or more) delays between radiofrequency saturation pulses in pulsed CEST, producing a series of CEST images sensitive to the speed of saturation transfer. Subtracting two images or fitting a time series produces CEST and relayed-nuclear Overhauser enhancement CEST maps without effects of direct water saturation and, when using low radiofrequency power, minimal magnetization transfer contrast interference. When applied to several model systems (bovine serum albumin, crosslinked bovine serum albumin, l-glutamic acid) and in vivo on healthy rat brain, VDMP-CEST showed sensitivity to slow to intermediate range magnetization transfer processes (rate < 100-150 Hz), such as amide proton transfer and relayed nuclear Overhauser enhancement-CEST. Images for these contrasts could be acquired in short scan times by using a single radiofrequency frequency. VDMP-CEST provides an approach to detect CEST effect by sensitizing saturation experiments to slower exchange processes without interference of direct water saturation and without need to acquire Z-spectra and perform asymmetry analysis. Copyright © 2013 Wiley Periodicals, Inc.

  13. Black phosphorus saturable absorber for ultrashort pulse generation

    Energy Technology Data Exchange (ETDEWEB)

    Sotor, J., E-mail: jaroslaw.sotor@pwr.edu.pl; Sobon, G.; Abramski, K. M. [Laser and Fiber Electronics Group, Wroclaw University of Technology, Wybrzeze Wyspianskiego 27, Wroclaw 50-370 (Poland); Macherzynski, W.; Paletko, P. [Faculty of Microsystem Electronics and Photonics, Wroclaw University of Technology, Janiszewskiego 11/17, Wroclaw 50-372 (Poland)

    2015-08-03

    Low-dimensional materials, due to their unique and versatile properties, are very interesting for numerous applications in electronics and optoelectronics. Recently rediscovered black phosphorus, with a graphite-like layered structure, can be effectively exfoliated up to the single atomic layer called phosphorene. Contrary to graphene, it possesses a direct band gap controllable by the number of stacked atomic layers. For those reasons, black phosphorus is now intensively investigated and can complement or replace graphene in various photonics and electronics applications. Here, we demonstrate that black phosphorus can serve as a broadband saturable absorber and can be used for ultrashort optical pulse generation. The mechanically exfoliated ∼300 nm thick layers of black phosphorus were transferred onto the fiber core, and under pulsed excitation at 1560 nm wavelength, its transmission increases by 4.6%. We have demonstrated that the saturable absorption of black phosphorus is polarization sensitive. The fabricated device was used to mode-lock an Er-doped fiber laser. The generated optical solitons with the 10.2 nm bandwidth and 272 fs duration were centered at 1550 nm. The obtained results unambiguously show that black phosphorus can be effectively used for ultrashort pulse generation with performances similar or even better than currently used graphene or carbon nanotubes. This application of black phosphorus proves its great potential to future practical use in photonics.

  14. Influence of aerobic exercise training on post-exercise responses of aortic pulse pressure and augmentation pressure in postmenopausal women

    OpenAIRE

    Akazawa, Nobuhiko; Ra, Song-Gyu; Sugawara, Jun; Maeda, Seiji

    2015-01-01

    Central arterial blood pressure (BP) is more predictive of future cardiovascular events than is brachial BP because it reflects the BP load imposed on the left ventricle with greater accuracy. However, little is known about the effects of exercise training on central hemodynamic response to acute exercise. The purpose of the present study was to determine the influence of an aerobic exercise regimen on the response of aortic BP after a single aerobic exercise in postmenopausal women. Nine hea...

  15. A comparative study on dual colour soft aperture cascaded second ...

    Indian Academy of Sciences (India)

    2014-02-09

    Feb 9, 2014 ... ... cw mode-locked pulse train with pulse duration 10.3 ps and average power of 1.84 W and 255 mW at 1064 nm and 532 nm respectively for the optimum performance in type-II KTP crystal. The exceptional stability achieved with KTP is accounted by simulating the mode-size variation with phase mismatch.

  16. FY07 LDRD Final Report Precision, Split Beam, Chirped-Pulse, Seed Laser Technology

    Energy Technology Data Exchange (ETDEWEB)

    Dawson, J W; Messerly, M J; Phan, H H; Crane, J K; Beach, R J; Siders, C W; Barty, C J

    2009-11-12

    The goal of this LDRD ER was to develop a robust and reliable technology to seed high-energy laser systems with chirped pulses that can be amplified to kilo-Joule energies and recompressed to sub-picosecond pulse widths creating extremely high peak powers suitable for petawatt class physics experiments. This LDRD project focused on the development of optical fiber laser technologies compatible with the current long pulse National Ignition Facility (NIF) seed laser. New technologies developed under this project include, high stability mode-locked fiber lasers, fiber based techniques for reduction of compressed pulse pedestals and prepulses, new compact stretchers based on chirped fiber Bragg gratings (CFBGs), new techniques for manipulation of chirped pulses prior to amplification and new high-energy fiber amplifiers. This project was highly successful and met virtually all of its goals. The National Ignition Campaign has found the results of this work to be very helpful. The LDRD developed system is being employed in experiments to engineer the Advanced Radiographic Capability (ARC) front end and the fully engineered version of the ARC Front End will employ much of the technology and techniques developed here.

  17. Pulse retrieval algorithm for interferometric frequency-resolved optical gating based on differential evolution.

    Science.gov (United States)

    Hyyti, Janne; Escoto, Esmerando; Steinmeyer, Günter

    2017-10-01

    A novel algorithm for the ultrashort laser pulse characterization method of interferometric frequency-resolved optical gating (iFROG) is presented. Based on a genetic method, namely, differential evolution, the algorithm can exploit all available information of an iFROG measurement to retrieve the complex electric field of a pulse. The retrieval is subjected to a series of numerical tests to prove the robustness of the algorithm against experimental artifacts and noise. These tests show that the integrated error-correction mechanisms of the iFROG method can be successfully used to remove the effect from timing errors and spectrally varying efficiency in the detection. Moreover, the accuracy and noise resilience of the new algorithm are shown to outperform retrieval based on the generalized projections algorithm, which is widely used as the standard method in FROG retrieval. The differential evolution algorithm is further validated with experimental data, measured with unamplified three-cycle pulses from a mode-locked Ti:sapphire laser. Additionally introducing group delay dispersion in the beam path, the retrieval results show excellent agreement with independent measurements with a commercial pulse measurement device based on spectral phase interferometry for direct electric-field retrieval. Further experimental tests with strongly attenuated pulses indicate resilience of differential-evolution-based retrieval against massive measurement noise.

  18. A self-starting hybrid optoelectronic oscillator generating ultra low jitter 10-GHz optical pulses and low phase noise electrical signals

    DEFF Research Database (Denmark)

    Lasri, J.; Bilenca, A.; Dahan, D.

    2002-01-01

    In this letter, we describe a self-starting optical pulse source generating ultra low noise 15-ps-wide pulses at 10 GHz. It is based on a hybrid optoelectronic oscillator comprising a fiber extended cavity mode-locked diode laser which injection locks a self-oscillating heterojunction bipolar...... phototransistor. Average jitter levels of 40-43 fs and an amplitude noise of 0.1-0.15% over a frequency range of 500 Hz-15 kHz or 500 Hz-1 MHz were obtained, respectively. The noise is slightly larger, a 57- fs jitter and 0.2% amplitude noise, for a frequency range of 100 Hz-1 MHz. A 10-GHz electrical signal...... with a low phase noise (-108 dBc/Hz at 10-kHz offset from the carrier) is also generated....

  19. Pulse Generator

    Science.gov (United States)

    Greer, Lawrence (Inventor)

    2017-01-01

    An apparatus and a computer-implemented method for generating pulses synchronized to a rising edge of a tachometer signal from rotating machinery are disclosed. For example, in one embodiment, a pulse state machine may be configured to generate a plurality of pulses, and a period state machine may be configured to determine a period for each of the plurality of pulses.

  20. Selective ablation of dental enamel and dentin using femtosecond laser pulses

    International Nuclear Information System (INIS)

    Lizarelli, R F Z; Costa, M M; Carvalho-Filho, E; Bagnato, V S; Nunes, F D

    2008-01-01

    The study of the interaction of intense laser light with matter, as well as transient response of atoms and molecules is very appropriated because of the laser energy concentration in a femtosecond optical pulses. The fundamental problem to be solved is to find tools and techniques which allow us to observe and manipulate on a femtosecond time scale the photonics events on and into the matter. Six third human extracted molars were exposed to a femtosecond Ti:Sapphire Q-switched and mode locked laser (Libra-S, Coherent, Palo Alto, CA, USA), emitting pulses with 70 fs width, radiation wavelength of 801 nm, at a constant pulse repetition rate of 1 KHz. The laser was operated at different power levels (70 to 400 mW) with constant exposition time of 10 seconds, at focused and defocused mode. Enamel and dentin surfaces were evaluated concerned ablation rate and morphological aspects under scanning electron microscopic. The results in this present experiment suggest that at the focused mode and under higher average power, enamel tissues present microcavities with higher depth and very precise edges, but, while dentin shows a larger melt-flushing, lower depth and melting and solidification aspect. In conclusion, it is possible to choose hard or soft ablation, under lower and higher average power, respectively, revealing different aspects of dental enamel and dentin, depending on the average power, fluence and distance from the focal point of the ultra-short pulse laser on the tooth surface

  1. Compact pulse repetition rate multiplication scheme using micro ring resonator

    DEFF Research Database (Denmark)

    Ji, Hua; Pu, Minhao; Galili, Michael

    2009-01-01

    A compact repetition rate multiplier using a micro ring resonator is experimentally demonstrated. Combined with an amplitude equalizer, a 40 GHz pulse train is achieved from a 10 GHz input pulse train....

  2. Mode-locked Bloch oscillations in a ring cavity

    International Nuclear Information System (INIS)

    Samoylova, M; Piovella, N; Hunter, D; Robb, G R M; Bachelard, R; Courteille, Ph W

    2014-01-01

    We present a new technique for stabilizing and monitoring Bloch oscillations of ultracold atoms in an optical lattice under the action of a constant external force. In the proposed scheme, the atoms also interact with a unidirectionally pumped optical ring cavity whose one arm is collinear with the optical lattice. For weak collective coupling, Bloch oscillations dominate over the collective atomic recoil lasing instability and develop a synchronized regime in which the atoms periodically exchange momentum with the cavity field. (letter)

  3. Non-Pulse-Leakage 100-kHz Level, High Beam Quality Industrial Grade Nd:YVO4 Picosecond Amplifier

    Directory of Open Access Journals (Sweden)

    Zhenao Bai

    2017-06-01

    Full Text Available A non-pulse-leakage optical fiber pumped 100-kHz level high beam quality Nd:YVO4 picosecond amplifier has been developed. An 80 MHz, 11.5 ps mode-locked picosecond laser is used as the seed with single pulse energy of 1 nJ. By harnessing the double β-BaB2O4 (BBO crystal Pockels cells in both the pulse picker and regenerative amplifier, the seed pulse leakage of the output is suppressed effectively with an adjustable repetition rate from 200 to 500 kHz. Through one stage traveling-wave amplifier, a maximum output power of 24.5 W is generated corresponding to the injected regenerative amplified power of 9.73 W at 500 kHz. The output pulse duration is 16.9 ps, and the beam quality factor M2 is measured to be 1.25 with near-field roundness higher than 99% at the full output power.

  4. PULSE GENERATOR

    Science.gov (United States)

    Roeschke, C.W.

    1957-09-24

    An improvement in pulse generators is described by which there are produced pulses of a duration from about 1 to 10 microseconds with a truly flat top and extremely rapid rise and fall. The pulses are produced by triggering from a separate input or by modifying the current to operate as a free-running pulse generator. In its broad aspect, the disclosed pulse generator comprises a first tube with an anode capacitor and grid circuit which controls the firing; a second tube series connected in the cathode circuit of the first tube such that discharge of the first tube places a voltage across it as the leading edge of the desired pulse; and an integrator circuit from the plate across the grid of the second tube to control the discharge time of the second tube, determining the pulse length.

  5. Reconstruction of Attosecond Pulse Trains

    Science.gov (United States)

    Mairesse, Y.; Agostini, P.; Breger, P.; Carre, B.; Merdji, A.; Monchicourt, P.; Salieres, P.; Varju, K.; Gustafsson, E.; Johnsson, P.; Mauritsson, J.; Remetter, T.; L'Huillier, A.; Frasinski, L. J.

    2006-11-01

    We show that it is possible to completely reconstruct the intensity profile of the attosecond bursts emitted as a superposition of high harmonics from a series of RABBIT measurements carried out at different infrared intensities. The electric field can be recovered from a measurement of the central harmonic chirp. Timing, chirp and variations of the carrier-to-envelope phase of the attosecond bursts are accessible to the proposed method.

  6. Time-correlated pulse trains

    International Nuclear Information System (INIS)

    Brunson, G.S.

    1985-01-01

    This describes the status of some current work in the Advanced Nuclear Technology Group at Los Alamos. The authors have at least two distinct objectives in the statistical analysis of neutron signal streams. On one hand, they want to identify spontaneous fission neutrons in nuclear waste as a means of measuring the quantity of transuranic material in a waste drum (or other package). On the other hand, they want to use the same or similar techniques in measuring reactivity in multiplying systems. These two applications differ in several important ways but, nevertheless, have much in common. Essentially, there is the need to determine the extent to which the coherence of chain-related neutrons cause the statistics of the signal stream to depart from Poisson expectation

  7. Generation of 15 nJ pulses from a highly efficient, low-cost multipass-cavity Cr3+:LiCAF laser.

    Science.gov (United States)

    Demirbas, Umit; Sennaroglu, Alphan; Kärtner, Franz X; Fujimoto, James G

    2009-02-15

    We describe the generation of enhanced pulse energies using a multipass-cavity (MPC) Cr(3)+:LiCAF laser, pumped by inexpensive, single spatial mode laser diodes. A semiconductor saturable absorber was used for stable mode-locked operation. The MPC reduced the pulse repetition rate to the approximately 10 MHz level, scaling pulse energies and intensities. With only 540 mW of absorbed pump power, 98 fs pulses with energies of 9.9 nJ and peak powers of approximately 101 kW, corresponding to 95 mW of average power at a repetition rate of 9.58 MHz, were generated. By increasing the intracavity negative dispersion, 310 fs pulses with energies of 15.2 nJ and peak powers of approximately 49 kW, corresponding to 160 mW of average power at 10.51 MHz repletion rate, were also generated. These results demonstrate that low-cost MPC Cr(3+)-doped colquiriite lasers can generate pulse energies and intensities comparable to more expensive Ti:sapphire lasers.

  8. Pulse Oximetry

    Science.gov (United States)

    ... American Thoracic Society www. thoracic. org American Thoracic Society PATIENT EDUCATION | INFORMATION SERIES How accurate is the pulse oximeter? The ... patient. co. uk/ doctor/ Pulse- Oximetry. htm This ... service of the American Thoracic Society. The content is for educational purposes only. It ...

  9. Current Extensions on PULSE

    Directory of Open Access Journals (Sweden)

    Sanda Dragos

    2010-09-01

    Full Text Available Using a learning management system (LMS is a common practise nowadays. Such instruments are used in educational institutions to enhance and support the teaching act as well as in industry for training purposes. In a computer science department of an university such instrument tends to be a basic requirement. That is because not only it allows a better management of courses and a better communication between students and professors, but can also serve as a perfect instrument for presenting teaching related materials for computer science subjects. During the years I have created and used several such instruments: a System with Interactive ackNowledgement and Evaluation of students work during laboratory sessions (SINE, a Php Utility used in Laboratories for Student Evaluation (PULSE, and PULSE Extended. The aim of this paper is to present the current enhancements of PULSE.

  10. 175 fs-long pulses from a high-power single-mode Er-doped fiber laser at 1550 nm

    Science.gov (United States)

    Elahi, Parviz; Kalaycıoğlu, Hamit; Li, Huihui; Akçaalan, Önder; Ilday, F. Ömer

    2017-11-01

    Development of Er-doped ultrafast lasers have lagged behind the corresponding developments in Yb- and Tm-doped lasers, in particular, fiber lasers. Various applications benefit from operation at a central wavelength of 1.5 μm and its second harmonic, including emerging applications such as 3D processing of silicon and 3D printing based on two-photon polymerization. We report a simple, robust fiber master oscillator power amplifier operating at 1.55 μm, implementing chirp pulse amplification using single-mode fibers for diffraction-limited beam quality. The laser generates 80 nJ pulses at a repetition rate of 43 MHz, corresponding to an average power of 3.5 W, which can be compressed down to 175 fs. The generation of short pulses was achieved using a design which is guided by numerical simulations of pulse propagation and amplification and manages to overturn gain narrowing with self-phase modulation, without invoking excessive Raman scattering processes. The seed source for the two-stage amplifier is a dispersion-managed passively mode-locked oscillator, which generates a ∼40 nm-wide spectrum and 1.7-ps linearly chirped pulses.

  11. Nanosurgery of cells and chromosomes using near-infrared twelve-femtosecond laser pulses.

    Science.gov (United States)

    Uchugonova, Aisada; Lessel, Matthias; Nietzsche, Sander; Zeitz, Christian; Jacobs, Karin; Lemke, Cornelius; König, Karsten

    2012-10-01

    ABSTRACT. Laser-assisted surgery based on multiphoton absorption of near-infrared laser light has great potential for high precision surgery at various depths within the cells and tissues. Clinical applications include refractive surgery (fs-LASIK). The non-contact laser method also supports contamination-free cell nanosurgery. In this paper we describe usage of an ultrashort femtosecond laser scanning microscope for sub-100 nm surgery of human cells and metaphase chromosomes. A mode-locked 85 MHz Ti:Sapphire laser with an M-shaped ultrabroad band spectrum (maxima: 770  nm/830  nm) and an in situ pulse duration at the target ranging from 12 fs up to 3 ps was employed. The effects of laser nanoprocessing in cells and chromosomes have been quantified by atomic force microscopy. These studies demonstrate the potential of extreme ultrashort femtosecond laser pulses at low mean milliwatt powers for sub-100 nm surgery of cells and cellular organelles.

  12. Complex pulsing schemes for high frame rate imaging

    DEFF Research Database (Denmark)

    Misaridis, Thanassis; Fink, Mathias; Jensen, Jørgen Arendt

    2002-01-01

    up to a pulse train. The acoustically generated high time-bandwidth (TB) product waveforms can be compressed by using a filter bank of matched filters one for every beam direction. Matched filtering compresses the pulse train to a single pulse at the scatterer position plus a number of spike axial...

  13. Detection and visualization to Doppler sensitive sonar pulses

    NARCIS (Netherlands)

    Bertrand, D.B.; IJsselmuide, S.P. van; Beerens, S.P.

    2006-01-01

    In anti-submarine warfare, the use of Doppler sensitive sonar pulses is common practice. In particular, the wideband Doppler sensitive PTFM pulse (Pulse Train Frequency Modulation) is a powerful tool for detection in reverberation limited conditions. Nevertheless, this pulse is not operationally

  14. Emission Spectral Control of a Silicon Light Emitting Diode Fabricated by Dressed-Photon-Phonon Assisted Annealing Using a Short Pulse Pair

    Directory of Open Access Journals (Sweden)

    Tadashi Kawazoe

    2014-01-01

    Full Text Available We fabricated a high-efficiency infrared light emitting diode (LED via dressed-photon-phonon (DPP assisted annealing of a p-n homojunctioned bulk Si crystal. The center wavelength in the electroluminescence (EL spectrum of this LED was determined by the wavelength of a CW laser used in the DPP-assisted annealing. We have proposed a novel method of controlling the EL spectral shape by additionally using a pulsed light source in order to control the number of phonons for the DPP-assisted annealing. In this method, the Si crystal is irradiated with a pair of pulses having an arrival time difference between them. The number of coherent phonons created is increased (reduced by tuning (detuning this time difference. A Si-LED was subjected to DPP-assisted annealing using a 1.3 μm (hν=0.94 eV CW laser and a mode-locked pulsed laser with a pulse width of 17 fs. When the number of phonons was increased, the EL emission spectrum broadened toward the high-energy side by 200 meV or more. The broadening towards the low-energy side was reduced to 120 meV.

  15. Anomalous pulse interaction in dissipative media

    Science.gov (United States)

    Bordyugov, Grigory; Engel, Harald

    2008-06-01

    We review a number of phenomena occurring in one-dimensional excitable media due to modified decay behind propagating pulses. Those phenomena can be grouped in two categories depending on whether the wake of a solitary pulse is oscillatory or not. Oscillatory decay leads to nonannihilative head-on collision of pulses and oscillatory dispersion relation of periodic pulse trains. Stronger wake oscillations can even result in a bistable dispersion relation. Those effects are illustrated with the help of the Oregonator and FitzHugh-Nagumo models for excitable media. For a monotonic wake, we show that it is possible to induce bound states of solitary pulses and anomalous dispersion of periodic pulse trains by introducing nonlocal spatial coupling to the excitable medium.

  16. Pulsed power

    International Nuclear Information System (INIS)

    Anon.

    1977-01-01

    The key element of our pulsed power program is concentration of power in time and space by suppression of breakdown in dielectrics and in vacuum. Magnetically insulated vacuum transmission lines and magnetic suppression of insulator flashover have continued as the main reserch directions. Vacuum insulated line studies at Physics International have been expanded and a test bed at Sandia, called MITE (Magnetically Insulated Transmission Experiment), is under development. The choice for the baseline EBFA design will depend on the outcome of these studies and should be made in July 1977. The slow and intermediate speed pulsed power approaches to EBFA will be based on Proto I and Proto II results and several of the projected EBFA subsystems are presently being tested in Proto II. A further stage of power concentration, within the vacuum diode itself, would considerably ease the burden on dielectrics; methods of power multiplication involving magnetically imploded plasmas are being considered and tests have begun using the Ripple III apparatus

  17. Generation of high fidelity 62-fs, 7-nJ pulses at 1035 nm from a net normal-dispersion Yb-fiber laser with anomalous dispersion higher-order-mode fiber.

    Science.gov (United States)

    Zhu, L; Verhoef, A J; Jespersen, K G; Kalashnikov, V L; Grüner-Nielsen, L; Lorenc, D; Baltuška, A; Fernández, A

    2013-07-15

    Fiber oscillators operating in the normal dispersion regime allow generating high energy output pulses. The best stability of such oscillators is observed when the intracavity dispersion is close to zero. Intracavity dispersion compensation in such oscillators can be achieved using a higher-order mode fiber, which substantially reduces the higher order dispersion compared to all-normal dispersion oscillators or oscillators using intracavity gratings for dispersion compensation. Using this approach, we are able to obtain relatively high energy pulses, with high fidelity. Our modeling based on an analytic approach for oscillators operating in the normal dispersion regime predicts that at intermediate pulse energies an almost flat chirp can be obtained at the oscillator output enabling good pulse compression with a grating compressor close to Fourier limited duration. Here, we present a mode-locked ytterbium-doped fiber oscillator with a higher-order mode fiber operating in the net normal-dispersion regime, delivering 7.2 nJ pulses that can be dechirped down to 62 fs using a simple grating compressor.

  18. Pramana – Journal of Physics | Indian Academy of Sciences

    Indian Academy of Sciences (India)

    2014-02-09

    Feb 9, 2014 ... The laser delivers stable dual wavelength cw mode-locked pulse train with pulse duration 10.3 ps and average power of 1.84 W and 255 mW at 1064 nm and 532 nm respectively for the optimum performance in type-II KTP crystal. The exceptional stability achieved with KTP is accounted by simulating the ...

  19. Laser pulse shaping for high gradient accelerators

    Energy Technology Data Exchange (ETDEWEB)

    Villa, F., E-mail: fabio.villa@lnf.infn.it [INFN-Laboratori Nazionali di Frascati, via E. Fermi 40, 00044 Frascati (Italy); Anania, M.P.; Bellaveglia, M. [INFN-Laboratori Nazionali di Frascati, via E. Fermi 40, 00044 Frascati (Italy); Bisesto, F. [INFN-Laboratori Nazionali di Frascati, via E. Fermi 40, 00044 Frascati (Italy); Università La Sapienza di Roma, Via A. Scarpa 14, Rome (Italy); Chiadroni, E. [INFN-Laboratori Nazionali di Frascati, via E. Fermi 40, 00044 Frascati (Italy); Cianchi, A. [INFN-Roma Tor Vergata and Università di Roma Tor Vergata, Via della Ricerca Scientifica 1, 00133 Rome (Italy); Curcio, A.; Galletti, M.; Di Giovenale, D.; Di Pirro, G.; Ferrario, M.; Gatti, G. [INFN-Laboratori Nazionali di Frascati, via E. Fermi 40, 00044 Frascati (Italy); Moreno, M.; Petrarca, M. [Università La Sapienza di Roma, Via A. Scarpa 14, Rome (Italy); Pompili, R.; Vaccarezza, C. [INFN-Laboratori Nazionali di Frascati, via E. Fermi 40, 00044 Frascati (Italy)

    2016-09-01

    In many high gradient accelerator schemes, i.e. with plasma or dielectric wakefield induced by particles, many electron pulses are required to drive the acceleration of one of them. Those electron bunches, that generally should have very short duration and low emittance, can be generated in photoinjectors driven by a train of laser pulses coming inside the same RF bucket. We present the system used to shape and characterize the laser pulses used in multibunch operations at Sparc-lab. Our system gives us control over the main parameter useful to produce a train of up to five high brightness bunches with tailored intensity and time distribution.

  20. Photoionization of water molecules by a train of attosecond pulses assisted by a near-infrared laser: delay and polarization control

    Science.gov (United States)

    Martini, Lara; Boll, Diego I. R.; Fojón, Omar A.

    2017-08-01

    Basic reactions involving water molecules are essential to understand the interaction between radiation and the biological tissue because living cells are composed mostly by water. Therefore, the knowledge of ionization of the latter is crucial in many domains of Biology and Physics. So, we study theoretically the photoionization of water molecules by extreme ultraviolet attopulse trains assisted by lasers in the near-infrared range. We use a separable Coulomb-Volkov model in which the temporal evolution of the system can be divided into three stages allowing spatial and temporal separation for the Coulomb and Volkov final state wavefunctions. First, we analyze photoelectron angular distributions for different delays between the attopulse train and the assistant laser field. We compare our results for water and Ne atoms as they belong to the same isoelectronic series. Moreover, we contrast our calculations with previous theoretical and experimental work for Ar atoms due to the similarities of the orbitals involved in the reaction. Second, we study the effect of varying the relative orientations of the attopulse and laser field polarizations and we compare our predictions with other theories and experiments. We expect these studies contribute to the improvement of polarization experiments and the development of the attopulse trains and assistant laser fields technologies. Finally, we hope our work promote progress on the control of the chemical reactivity of water molecules since this could be useful in different fields such as radiobiology and medical physics.

  1. Pulse radiolysis

    International Nuclear Information System (INIS)

    Greenshields, H.; Seddon, W.A.

    1982-03-01

    This supplement to two bibliographies published in 1970 and 1972 lists 734 references to the literature of pulse radiolysis, arranged under eight broad subject headings. The references were compiled by searching Biological Abstracts, Chemical Abstracts, Nuclear Science Abstracts and the Weekly List of Papers in Radiation Chemistry issued by the Radiation Chemistry Data Center of Notre Dame University. Full bibliographic data is given for papers published in the period 1971 to 1974. A personal author index listing more than 600 authors and a similar number of co-authors is included

  2. PULSE COLUMN

    Science.gov (United States)

    Grimmett, E.S.

    1964-01-01

    This patent covers a continuous countercurrent liquidsolids contactor column having a number of contactor states each comprising a perforated plate, a layer of balls, and a downcomer tube; a liquid-pulsing piston; and a solids discharger formed of a conical section at the bottom of the column, and a tubular extension on the lowest downcomer terminating in the conical section. Between the conical section and the downcomer extension is formed a small annular opening, through which solids fall coming through the perforated plate of the lowest contactor stage. This annular opening is small enough that the pressure drop thereacross is greater than the pressure drop upward through the lowest contactor stage. (AEC)

  3. Method for pulse to pulse dose reproducibility applied to electron linear accelerators

    International Nuclear Information System (INIS)

    Ighigeanu, D.; Martin, D.; Oproiu, C.; Cirstea, E.; Craciun, G.

    2002-01-01

    An original method for obtaining programmed beam single shots and pulse trains with programmed pulse number, pulse repetition frequency, pulse duration and pulse dose is presented. It is particularly useful for automatic control of absorbed dose rate level, irradiation process control as well as in pulse radiolysis studies, single pulse dose measurement or for research experiments where pulse-to-pulse dose reproducibility is required. This method is applied to the electron linear accelerators, ALIN-10 of 6.23 MeV and 82 W and ALID-7, of 5.5 MeV and 670 W, built in NILPRP. In order to implement this method, the accelerator triggering system (ATS) consists of two branches: the gun branch and the magnetron branch. ATS, which synchronizes all the system units, delivers trigger pulses at a programmed repetition rate (up to 250 pulses/s) to the gun (80 kV, 10 A and 4 ms) and magnetron (45 kV, 100 A, and 4 ms).The accelerated electron beam existence is determined by the electron gun and magnetron pulses overlapping. The method consists in controlling the overlapping of pulses in order to deliver the beam in the desired sequence. This control is implemented by a discrete pulse position modulation of gun and/or magnetron pulses. The instabilities of the gun and magnetron transient regimes are avoided by operating the accelerator with no accelerated beam for a certain time. At the operator 'beam start' command, the ATS controls electron gun and magnetron pulses overlapping and the linac beam is generated. The pulse-to-pulse absorbed dose variation is thus considerably reduced. Programmed absorbed dose, irradiation time, beam pulse number or other external events may interrupt the coincidence between the gun and magnetron pulses. Slow absorbed dose variation is compensated by the control of the pulse duration and repetition frequency. Two methods are reported in the electron linear accelerators' development for obtaining the pulse to pulse dose reproducibility: the method

  4. Diffraction leveraged modulation of X-ray pulses using MEMS-based X-ray optics

    Energy Technology Data Exchange (ETDEWEB)

    Lopez, Daniel; Shenoy, Gopal; Wang, Jin; Walko, Donald A.; Jung, Il-Woong; Mukhopadhyay, Deepkishore

    2016-08-09

    A method and apparatus are provided for implementing Bragg-diffraction leveraged modulation of X-ray pulses using MicroElectroMechanical systems (MEMS) based diffractive optics. An oscillating crystalline MEMS device generates a controllable time-window for diffraction of the incident X-ray radiation. The Bragg-diffraction leveraged modulation of X-ray pulses includes isolating a particular pulse, spatially separating individual pulses, and spreading a single pulse from an X-ray pulse-train.

  5. Surface modification and laser pulse length effects on internal energy transfer in DIOS.

    Science.gov (United States)

    Luo, Guanghong; Chen, Yong; Siuzdak, Gary; Vertes, Akos

    2005-12-29

    Benzyl-substituted benzylpyridinium (BP) chloride salts were used as a source of thermometer ions to probe the internal energy (IE) transfer in desorption/ionization on porous silicon (DIOS). To modify their wetting properties and the interaction energies with the thermometer ions, the DIOS surfaces were silylated to produce trimethylsilyl- (TMS), amine- (NH2), perfluoroalkyl- (PFA), and perfluorophenyl-derivatized (PFP) surfaces. Two laser sources--a nitrogen laser with pulse length of 4 ns and a mode locked 3 x omega Nd:YAG laser with a pulse length of 22 ps--were utilized to induce desorption/ionization and fragmentation at various laser fluence levels. The corresponding survival yields were determined as indicators of the IE transfer and the IE distributions were extracted. In most cases, with increasing the laser fluence in a broad range (approximately 20 mJ/cm2), no change in IE transfer was observed. For ns excitation, this was in remarkable contrast with MALDI, where increasing the laser fluence resulted in sharply (within approximately 5 mJ/cm2) declining survival yields. Derivatization of the porous silicon surface did not affect the survival yields significantly but had a discernible effect on the threshold fluence for ion production. The IE distributions determined for DIOS and MALDI from alpha-cyano-4-hydroxycinnamic acid reveal that the mean IE value is always lower for the latter. Using the ps laser, the IE distribution is always narrower for DIOS, whereas for ns laser excitation the width depends on surface modification. Most of the differences between MALDI and DIOS described here are compatible with the different dimensionality of the plume expansion and the differences in the activation energy of desorption due to surface modifications.

  6. Pulse pile-up. II: Tailed pulses

    International Nuclear Information System (INIS)

    Wilkinson, D.H.

    1990-07-01

    The considerations of the preceding paper are extended to the case of pulses having infinite (exponential) tails. Exact solutions are presented for pure exponential pulses all of the same height; ruin theory is applied for pulses of more realistic form. (Author) (2 refs., 9 figs.)

  7. Random pulse generator

    International Nuclear Information System (INIS)

    Guo Ya'nan; Jin Dapeng; Zhao Dixin; Liu Zhen'an; Qiao Qiao; Chinese Academy of Sciences, Beijing

    2007-01-01

    Due to the randomness of radioactive decay and nuclear reaction, the signals from detectors are random in time. But normal pulse generator generates periodical pulses. To measure the performances of nuclear electronic devices under random inputs, a random generator is necessary. Types of random pulse generator are reviewed, 2 digital random pulse generators are introduced. (authors)

  8. Programmable pulse generator

    International Nuclear Information System (INIS)

    Xue Zhihua; Lou Binqiao; Duan Xiaohui

    2002-01-01

    The author introduces the design of programmable pulse generator that is based on a micro-controller and controlled by RS232 interface of personal computer. The whole system has good stability. The pulse generator can produce TTL pulse and analog pulse. The pulse frequency can be selected by EPLD. The voltage amplitude and pulse width of analog pulse can be adjusted by analog switches and digitally-controlled potentiometers. The software development tools of computer is National Instruments LabView5.1. The front panel of this virtual instrumentation is intuitive and easy-to-use. Parameters can be selected and changed conveniently by knob and slide

  9. Quantum dynamics of attosecond electron pulse compression

    Science.gov (United States)

    Baum, Peter

    2017-12-01

    If an electron beam is periodically modulated in velocity, for example by laser field cycles, it can transform upon further propagation into a train of attosecond or shorter electron pulses. Here, I investigate the quantum mechanics of such an approach by numerically solving the Schrödinger equation in the time domain. There is a limit for the shortest electron pulses that can be achieved, and it depends on simple relations between the electron energy, the laser period, and the modulation strength. These results allow to design future experiments and to compare the measured electron pulse shapes to their quantum limit.

  10. Pulsed water jet generated by pulse multiplication

    Czech Academy of Sciences Publication Activity Database

    Dvorský, R.; Sitek, Libor; Sochor, T.

    2016-01-01

    Roč. 23, č. 4 (2016), s. 959-967 ISSN 1330-3651 R&D Projects: GA MŠk(CZ) LO1406; GA MŠk ED2.1.00/03.0082 Institutional support: RVO:68145535 Keywords : high-pressure pulses * pulse intensifier * pulsed water jet * water hammer effect Subject RIV: JQ - Machines ; Tools Impact factor: 0.723, year: 2016 http://hrcak.srce.hr/163752?lang=en

  11. Faraday tarotion: new parameter for electromagnetic pulse propagation in magnetoplasma

    International Nuclear Information System (INIS)

    Bloch, S.C.; Lyons, P.W.

    1976-01-01

    Extreme distortion and time-dependent Faraday rotation occur for propagation of short electromagnetic pulses in magnetoplasma, for some ranges of plasma parameters. In order to relate pulse and monochromatic waves for propagation-path diagnostic purposes, a new parameter is introduced for the transmitted pulse train which has properties that correspond very accurately to results that would be expected for Faraday rotation of a continuous wave having the central frequency of the incident pulse spectrum. Results for 5-ns pulses (10 GHz) are presented for varying propagating length, static magnetic field, electron density, and collisional absorption

  12. Telemetry Standards, RCC Standard 106-17, Annex A.1, Pulse Amplitude Modulation Standards

    Science.gov (United States)

    2017-07-01

    Standard 106-17 Annex A.1, July 2017 A.1-iii Acronyms dB decibel FM frequency modulation IF intermediate frequency PAM pulse amplitude...standard defines the recommended pulse train structure and design characteristics for the implementation of pulse amplitude modulation (PAM) telemetry...between transitions in the PAM pulse train shall be limited by whichever is the narrower of the following: a. One-half of the 3-dB frequency of the

  13. Laser pulse stacking method

    Science.gov (United States)

    Moses, E.I.

    1992-12-01

    A laser pulse stacking method is disclosed. A problem with the prior art has been the generation of a series of laser beam pulses where the outer and inner regions of the beams are generated so as to form radially non-synchronous pulses. Such pulses thus have a non-uniform cross-sectional area with respect to the outer and inner edges of the pulses. The present invention provides a solution by combining the temporally non-uniform pulses in a stacking effect to thus provide a more uniform temporal synchronism over the beam diameter. 2 figs.

  14. Periodic dark pulse emission induced by delayed feedback in a quantum well semiconductor laser

    Directory of Open Access Journals (Sweden)

    L. Li

    2012-12-01

    Full Text Available We report the experimental observation of periodic dark pulse emission in a quantum-well semiconductor laser with delayed optical feedback. We found that under appropriate operation conditions the laser can also emit a stable train of dark pulses. The repetition frequency of the dark pulse is determined by the external cavity length. Splitting of the dark pulse was also observed. We speculate that the observed dark pulse is a kind of temporal cavity soliton formed in the laser.

  15. Pulse to pulse klystron diagnosis system

    International Nuclear Information System (INIS)

    Nowak, J.; Davidson, V.; Genova, L.; Johnson, R.; Reagan, D.

    1981-03-01

    This report describes a system used to study the behavior of SLAC high powered klystrons operating with a twice normal pulse width of 5 μs. At present, up to eight of the klystrons installed along the accelerator can be operated with long pulses and monitored by this system. The report will also discuss some of the recent findings and investigations

  16. Few-cycle isolated attosecond pulses

    International Nuclear Information System (INIS)

    Sansone, G.; Benedetti, E.; Calegari, F.; Stagira, S.; Vozzi, C.; Silvestri De, S.; Nisoli, M.

    2006-01-01

    indicates the presence of a predominant second order dispersion (positive chirp), which is intrinsic to the XUV generation process. As recently demonstrated in the case of trains of attosecond pulses, the positive chirp of the radiation produced by high-order harmonic generation can be compensated for by the negative group delay dispersion of thin aluminum foils. Upon increasing the thickness of an aluminum plate we have obtained XUV pulses with duration shorter than 300 as (at 37 eV), thus corresponding to few cycles of the electric field.

  17. Pulse width modulation inverter with battery charger

    Science.gov (United States)

    Slicker, James M. (Inventor)

    1985-01-01

    An inverter is connected between a source of DC power and a three-phase AC induction motor, and a microprocessor-based circuit controls the inverter using pulse width modulation techniques. In the disclosed method of pulse width modulation, both edges of each pulse of a carrier pulse train are equally modulated by a time proportional to sin .theta., where .theta. is the angular displacement of the pulse center at the motor stator frequency from a fixed reference point on the carrier waveform. The carrier waveform frequency is a multiple of the motor stator frequency. The modulated pulse train is then applied to each of the motor phase inputs with respective phase shifts of 120.degree. at the stator frequency. Switching control commands for electronic switches in the inverter are stored in a random access memory (RAM) and the locations of the RAM are successively read out in a cyclic manner, each bit of a given RAM location controlling a respective phase input of the motor. The DC power source preferably comprises rechargeable batteries and all but one of the electronic switches in the inverter can be disabled, the remaining electronic switch being part of a flyback DC-DC converter circuit for recharging the battery.

  18. New algorithms and pulse-processing units in radioisotope instruments

    International Nuclear Information System (INIS)

    Antonjak, V.; Gonsjorowski, L.; Jastschuk, E.; Kwasnewski, T.

    1981-01-01

    Three new algorithms and the corresponding electronic circuits are described, beginning with the automatic gain stabilisation circuit for scintillation counters. The signal obtained as the difference between two pulse trains from amplitude discriminators has been used for photomultiplier high voltage control. Furthermore, a real time digital filter for random pulse trains is presented, showing that the variance of pulse trains is decreasing after passing the filter. The block diagram, principle of operation and basic features of the filter are given. Finally, a digital circuit for polynomial linearization of the scale function in radioisotope instruments is described. Again, the block diagram of pulse train processing, the mode of operation and programming method are given. (author)

  19. ELECTRICAL PULSE COUNTER APPARATUS

    Science.gov (United States)

    Kaufman, W.M.; Jeeves, T.A.

    1962-09-01

    A progressive electrical pulse counter circuit rs designed for the counting of a chain of input pulses. The circuit employs a series of direct connected bistable counting stages simultaneously pulsed by each input pulse and a delay means connected between each of the stages. Each bistable stage has two d-c operative states, which stage, when in its initial state, prevents the next succeeding stage from changing its condition when the latter stage is pulsed. Since the delay circuits between the stages prevents the immediate decay of the d-c state of each stage when the stages are pulsed, only one stage will change its state for each input pulse, thereby providing progressive stage-by-stage counting. (AEC)

  20. Mechanism of merging of torsional Alfven and slow magnetosonic waves produced by train of laser pulses upon irradiation of a target located in a space plasma with a magnetic field. Laboratory modeling

    Science.gov (United States)

    Tischenko, V. N.; Zakharov, Yu. P.; Posukh, V. G.; Berezutsky, A. G.; Boyarintsev, E. L.; Melekhov, A. V.; Miroshnichenko, I. B.; Shaikhislamov, I. F.

    2017-10-01

    Experimentally, conditions under which a train of periodic laser plasma bunches creates a train of Alfven and a single slow magnetosonic waves which propagate in a tube of the geomagnetic field in the ionosphere were determined.

  1. Tunable THz Generation by the Interaction of a Super-luminous Laser Pulse with Biased Semiconductor Plasma

    International Nuclear Information System (INIS)

    Papadopoulos, K.; Zigler, A.

    2006-01-01

    Terahertz (THz) radiation is electromagnetic radiation in the range between several hundred and a few thousand GHz. It covers the gap between fast-wave electronics (millimeter waves) and optics (infrared). This spectral region offers enormous potential for detection of explosives and chemical/biological agents, non-destructive testing of non-metallic structural materials and coatings of aircraft structures, medical imaging, bio-sensing of DNA stretching modes and high-altitude secure communications. The development of these applications has been hindered by the lack of powerful, tunable THz sources with controlled waveform. The need for such sources is accentuated by the strong, but selective absorption of THz radiation during transmission through air with high vapor content. The majority of the current experimental work relies on time-domain spectroscopy using fast electrically biased photoconductive sources in conjunction with femto-second mode-locked Ti:Sapphire lasers. These sources known as Large Aperture Photoconductive Antennas (LAPA) have very limited tunability, relatively low upper bound of power and no bandwidth control. The paper presents a novel source of THz radiation known as Miniature Photoconductive Capacitor Array (MPCA). Experiments demonstrated tunability between .1 - 2 THz, control of the relative bandwidth Δf/f between .5-.01, and controlled pulse length and pulse waveform (temporal shape, chirp, pulse-to-pulse modulation etc.). Direct scaling from the current device indicates efficiency in excess of 30% at 1 THz with 1/f2 scaling at higher frequencies, peak power of 100 kW and average power between .1-1 W. The physics underlying the MPCA is the interaction of a super-luminous ionization front generated by the oblique incidence of a Ti:Sapphire laser pulse on a semiconductor crystal (ZnSe) biased with an alternating electrostatic field, similar to that of a frozen wave generator. It is shown theoretically and experimentally that the

  2. Power pulsing of the CMOS sensor Mimosa 26

    Energy Technology Data Exchange (ETDEWEB)

    Kuprash, Oleg [Deutsches Elektronen-Synchrotron (DESY), Hamburg (Germany); Universitaet Hamburg, Bundesstrasse 55 (Geomatikum), Hamburg 20146 (Germany); Bachynska, Olena; Gregor, Ingrid-Maria; Koetz, Ulrich [Deutsches Elektronen-Synchrotron (DESY), Hamburg (Germany)

    2013-07-01

    Mimosa 26 is a monolithic active pixel sensor developed by IPHC (Strasbourg) as a first prototype for the ILC vertex detector studies. The resolution requirements for the ILC tracking detector are very extreme, demanding very low material in the detector, thus only air cooling can be considered. Power consumption has to be reduced as far as possible. The beam structure of the ILC allows the possibility of power pulsing: only for about the 1 ms long bunch train full power is required, and during the 199 ms long pauses between the bunch trains the power can be reduced to a minimum. Not being adopted for the power pulsing, the sensor shows in laboratory tests a good performance under power pulsing. The power pulsing allows to significantly reduce the heating of the chip and divides power consumption approximately by a factor of 5. In this report a summary of power pulsing studies using the digital readout of Mimosa 26 is given.

  3. High voltage pulse conditioning

    International Nuclear Information System (INIS)

    Springfield, R.M.; Wheat, R.M.

    1990-01-01

    This patent describes an apparatus for conditioning high voltage pulses from particle accelerators in order to shorten the rise times of the pulses. Flashover switches in the cathode stalk of the transmission line hold off conduction for a determinable period of time, reflecting the early portion of the pulses. Diodes upstream of the switches divert energy into the magnetic and electrostatic storage of the capacitance and inductance inherent to the transmission line until the switches close

  4. Ultrashort Laser Pulse Phenomena

    CERN Document Server

    Diels, Jean-Claude

    2006-01-01

    Ultrashort Laser Pulse Phenomena, 2e serves as an introduction to the phenomena of ultra short laser pulses and describes how this technology can be used to examine problems in areas such as electromagnetism, optics, and quantum mechanics. Ultrashort Laser Pulse Phenomena combines theoretical backgrounds and experimental techniques and will serve as a manual on designing and constructing femtosecond (""faster than electronics"") systems or experiments from scratch. Beyond the simple optical system, the various sources of ultrashort pulses are presented, again with emphasis on the basic

  5. Opportunities in pulse combustion

    Science.gov (United States)

    Brenchley, D. L.; Bomelburg, H. J.

    1985-10-01

    In most pulse combustors, the combustion occurs near the closed end of a tube where inlet valves operate in phase with the pressure amplitude variations. Thus, within the combustion zone, both the temperature and the pressure oscillate around a mean value. However, the development of practical applications of pulse combustion has been hampered because effective design requires the right combination of the combustor's dimensions, valve characteristics, fuel/oxidizer combination, and flow pattern. Pulse combustion has several additional advantages for energy conversion efficiency, including high combustion and thermal efficiency, high combustion intensity, and high convective heat transfer rates. Also, pulse combustion can be self-aspirating, generating a pressure boost without using a blower. This allows the use of a compact heat exchanger that may include a condensing section and may obviate the need for a chimney. In the last decade, these features have revived interest in pulse combustion research and development, which has resulted in the development of a pulse combustion air heater by Lennox, and a pulse combustion hydronic unit by Hydrotherm, Inc. To appraise this potential for energy savings, a systematic study was conducted of the many past and present attempts to use pulse combustion for practical purposes. The authors recommended areas where pulse combustion technology could possibly be applied in the future and identified areas in which additional R and D would be necessary. Many of the results of the study project derived from a special workshop on pulse combustion. This document highlights the main points of the study report, with particular emphasis on pulse combustion application in chemical engineering.

  6. Monolithic mode-locked lasers with deeply dry etched Bragg mirror

    DEFF Research Database (Denmark)

    Larsson, David; Yvind, Kresten; Hvam, Jørn Märcher

    and high index regions (etched andunetched), is 240 nm for a 1st order grating and 480 nm for the 2nd order.Fabrication: The mask for the grating is formed by a combination of E-beam writing andUV-lithography. The resist pattern is transferred to a 100 nm SiO2-film, with a CHF3(Freon) based dry etch...

  7. Double pass locking and spatial mode locking for gravitational wave detectors

    CERN Document Server

    Cusack, B J; Slagmolen, B; Vine, G D; Gray, M B; McClelland, D E

    2002-01-01

    We present novel techniques for overcoming problems relating to the use of high-power lasers in mode cleaner cavities for second generation laser interferometric gravitational wave detectors. Rearranging the optical components into a double pass locking regime can help to protect locking detectors from damage. Modulator thermal lensing can be avoided by using a modulation-free technique such as tilt locking, or its recently developed cousin, flip locking.

  8. The role of dynamo fluctuations in anomalous ion heating, mode locking, and flow generation

    International Nuclear Information System (INIS)

    Terry, P.W.; Gatto, R.; Fiksel, G.; Fitzpatrick, R.; Hegna, C.C.

    2001-01-01

    Anomalous ion heating intrinsic to magnetic fluctuation-induced electron heat transport, the locking of global modes through wall conditions, and flow generation via the magnetic Reynolds stress all derive from the global, m=1 tearing modes familiar in the RFP as the dynamo modes. These important processes are investigated analytically and numerically, yielding new insights and predictions for comparison with experiment. (author)

  9. Conversion of Stability of Femtosecond Stabilized Mode-locked Laser to Optical Cavity Length

    Czech Academy of Sciences Publication Activity Database

    Šmíd, Radek; Číp, Ondřej; Čížek, Martin; Mikel, Břetislav; Lazar, Josef

    2010-01-01

    Roč. 57, č. 3 (2010), s. 636-640 ISSN 0885-3010 R&D Projects: GA ČR GA102/09/1276; GA MŠk(CZ) LC06007; GA MŠk 2C06012; GA MPO 2A-1TP1/127; GA MPO FT-TA3/133; GA MPO 2A-3TP1/113; GA ČR GA102/07/1179 Institutional research plan: CEZ:AV0Z20650511 Keywords : laser * Fabry-Perot * interferometer * length etalon Subject RIV: BH - Optics, Masers, Lasers Impact factor: 1.460, year: 2010

  10. MHD-mode locking by controlled halo-current in T-10 tokamak

    International Nuclear Information System (INIS)

    Ivanov, N.V.

    2002-01-01

    The experiment on a non-disruptive halo-current influence on the m=2 mode rotation at the steady-state stage of tokamak discharge is presented. The halo current in the (Rail Limiter - Plasma - Vacuum Chamber - External Circuit - Rail Limiter) loop was used. The switching on of an EMF source in the external circuit resulted in locking of the m=2 magnetic islands by the halo current of 400 A amplitude. This effect can be attributed to a coupling between the halo-current magnetic field and the m=2/n=1 mode. A set of magnetic probes was used to measure the halo-current space structure in plasma. The dimensions of the halo-current path in plasma along the magnetic field were much shorter in poloidal and toroidal directions than the corresponding wavelengths for m=2/n=1 mode. The experiment was simulated in the assumption that the tearing mode is affected by halo-current helical component with the same space structure. The equation for disturbed poloidal flux in presence of external helical surface current was used for the analysis. In calculations for T-10 conditions the halo-current affected the mode rotation frequency, like it was observed in the experiment. (author)

  11. Cryogenically-cooled Yb:YGAG ceramic mode-locked laser

    Czech Academy of Sciences Publication Activity Database

    Mužík, Jiří; Jelínek, M.; Jambunathan, Venkatesan; Miura, Taisuke; Smrž, Martin; Endo, Akira; Mocek, Tomáš; Kubeček, V.

    2015-01-01

    Roč. 24, č. 2 (2015), s. 1402-1408 ISSN 1094-4087 R&D Projects: GA MŠk ED2.1.00/01.0027; GA MŠk EE2.3.20.0143; GA MŠk LO1602; GA MŠk EE2.3.30.0057 Grant - others:HILASE(XE) CZ.1.05/2.1.00/01.0027; OP VK 6(XE) CZ.1.07/2.3.00/20.0143; OP VK 4 POSTDOK(XE) CZ.1.07/2.3.00/30.0057 Institutional support: RVO:68378271 Keywords : solid-states laser * lasing characteristics Subject RIV: BH - Optics, Masers, Lasers OBOR OECD: Optics (including laser optics and quantum optics) Impact factor: 3.148, year: 2015

  12. Effects of resonator input power on Kerr lens mode-locked lasers

    Indian Academy of Sciences (India)

    Pramana – Journal of Physics. Current Issue : Vol. 90, Issue 3 · Current Issue Volume 90 | Issue 3. March 2018. Home · Volumes & Issues · Special Issues · Forthcoming Articles · Search · Editorial Board · Information for Authors · Subscription ...

  13. Mode-Locked Deceleration of Molecular Beams: Physics with Ultracold Molecules

    Science.gov (United States)

    2017-02-07

    Enter name(s) of person(s) responsible for writing the report, performing the research, or credited with the content of the report. The form of entry...778 nm, which demonstrates an auto -scanning, interferometrically stable delay range of 1.5 cm. DISTRIBUTION A: Distribution approved for public release...that experiment has been moved to the NSF through their CAREER program. We also published two more theoretical papers with our colleagues at

  14. Effects of resonator input power on Kerr lens mode-locked lasers

    Indian Academy of Sciences (India)

    Additionally, in order to simplify the article, a Gaussian beam is considered. Figure 1. Resonator configuration for KLM laser: tilted mirrors M2 and M3 are focussing; output mirror M1 and back mirror M4 are flat; S1 and S2 are the slits;. L1 and L2 are the arms. The Kerr medium is placed between the mirrors M2 and M3.

  15. Broadband Fourier domain mode-locked laser for optical coherence tomography at 1060 nm

    DEFF Research Database (Denmark)

    Marschall, Sebastian; Klein, Thomas; Wieser, Wolfgang

    2012-01-01

    , enable acquisition of densely sampled three-dimensional datasets covering a wide field of view. However, semiconductor optical amplifiers (SOAs)-the typical laser gain media for swept sources-for the 1060nm band could until recently only provide relatively low output power and bandwidth. We have...

  16. Spatial instabilities of light bullets in passively-mode-locked lasers

    Science.gov (United States)

    Gurevich, S. V.; Javaloyes, J.

    2017-08-01

    Recently, the existence of robust three-dimensional light bullets (LBs) was predicted theoretically in the output of a laser coupled to a distant saturable absorber. In this paper, we analyze the stability and the range of existence of these dissipative localized structures and provide guidelines and realistic parameter sets for their experimental observation. In order to reduce the complexity of the analysis, we first approximate the three-dimensional problem by a reduced equation governing the dynamics of the transverse profile. This effective theory provides an intuitive picture of the LB formation mechanism. Moreover, it allows us to perform a detailed multiparameter bifurcation study and to identify the different mechanisms of instability. It is found that the LBs experience dominantly either homogeneous oscillation or symmetry-breaking transversal wave radiation. In addition, our analysis reveals several nonintuitive scaling behaviors as functions of the linewidth enhancement factors and the saturation parameters. Our results are confirmed by direct numerical simulations of the full system.

  17. Large-Scale Timing Distribution and RF-Synchronization for FEL Facilities

    CERN Document Server

    Kim, Jung Won; Kaertner, Franz X; Muecke, Oliver; Perrott, Michael

    2004-01-01

    For future advances in accelerator physics in general and seeding of FELs in particular, precise synchronization between seed radiation, low-level RF-systems and photo-injector laser is required. Typical synchronization methods based on direct photodetection are limited by the detector nonlinearities, which lead to amplitude-to-phase conversion and introduce timing jitter. A new synchronization scheme for extraction of low jitter RF-signals from optical pulse trains distributed by mode-locked lasers is proposed. It is robust against photodetector nonlinearities. The scheme is based on a transfer of timing information into an intensity imbalance between the two output beams from a Sagnac-loop interferometer. As a first experimental demonstration, sub-100 fs timing jitter between the extracted 2 GHz RF-signal and the 100 MHz optical pulse train from a mode-locked Ti:sapphire laser is demonstrated. Numerical simulations show that scaling to sub-femtosecond precision is possible. Together with mode-locked fiber l...

  18. Pulse duration discriminator

    International Nuclear Information System (INIS)

    Kosakovskij, L.F.

    1980-01-01

    Basic circuits of a discriminator for discrimination of pulses with the duration greater than the preset one, and of a multifunctional discriminator allowing to discriminate pulses with the duration greater (tsub(p)>tsub(s)) and lesser (tsub(p) tsub(s) and with the duration tsub(p) [ru

  19. PULSE HEIGHT ANALYZER

    Science.gov (United States)

    Johnstone, C.W.

    1958-01-21

    An anticoincidence device is described for a pair of adjacent channels of a multi-channel pulse height analyzer for preventing the lower channel from generating a count pulse in response to an input pulse when the input pulse has sufficient magnitude to reach the upper level channel. The anticoincidence circuit comprises a window amplifier, upper and lower level discriminators, and a biased-off amplifier. The output of the window amplifier is coupled to the inputs of the discriminators, the output of the upper level discriminator is connected to the resistance end of a series R-C network, the output of the lower level discriminator is coupled to the capacitance end of the R-C network, and the grid of the biased-off amplifier is coupled to the junction of the R-C network. In operation each discriminator produces a negative pulse output when the input pulse traverses its voltage setting. As a result of the connections to the R-C network, a trigger pulse will be sent to the biased-off amplifier when the incoming pulse level is sufficient to trigger only the lower level discriminator.

  20. Sources of pulsed radiation

    International Nuclear Information System (INIS)

    Sauer, M.C. Jr.

    1981-01-01

    Characteristics of various sources of pulsed radiation are examined from the viewpoint of their importance to the radiation chemist, and some examples of uses of such sources are mentioned. A summary is given of the application of methods of physical dosimetry to pulsed sources, and the calibration of convenient chemical dosimeters by physical dosimetry is outlined. 7 figures, 1 table

  1. Pulsed neutron generator

    International Nuclear Information System (INIS)

    Bespalov, D.F.; Bykovskii, Yu.A.; Vergun, I.I.; Kozlovskii, K.I.; Kozyrev, Yu.P.; Leonov, R.K.; Simagin, B.I.; Tsybin, A.S.; Shikanov, A.Ie.

    1986-03-01

    The paper describes a new device for generating pulsed neutron fields, utilized in nuclear geophysics for carrying out pulsed neutron logging and activation analysis under field conditions. The invention employs a sealed-off neutron tube with a laser ion source which increases neutron yield to the level of 10 neutrons per second or higher. 2 refs., 1 fig

  2. Gas phase pulse radiolysis

    International Nuclear Information System (INIS)

    Jonah, C.D.; Andong Liu; Mulac, W.A.

    1987-01-01

    Gas phase pulse radiolysis, a technique which can be used to study many different phenomena in chemistry and physics, is discussed. As a source of small radicals, pulse radiolysis is important to the field of chemistry, particularly to combustion and atmospheric kinetics. The reactions of 1,3-butadiene, allene, ethylene and acetylene with OH are presented. 52 refs., 1 fig., 1 tab

  3. Broadband CPMG sequence with short composite refocusing pulses

    Science.gov (United States)

    Koroleva, Van D. M.; Mandal, Soumyajit; Song, Yi-Qiao; Hürlimann, Martin D.

    2013-05-01

    We demonstrate that CPMG sequences with phase-modulated refocusing pulses of the same duration as the standard 180° pulses can generate echo trains with significantly increased amplitudes compared to the standard CPMG sequence in the case when there is a large range of Larmor frequencies across the sample. The best performance is achieved with symmetric phase-alternating (SPA) composite refocusing pulses of the form α-yβ+yα-y. In comparison to standard 180° pulses, we show that with SPA refocusing pulses with α ≈ 27° and β ≈ 126°, it is possible to double the signal-to-noise ratio without increasing the total pulse duration or power consumption of the refocusing pulses. The increased bandwidth of these pulses more than compensates for the decrease in performance in the vicinity of resonance. To achieve the full benefit of the broadband nature of the SPA pulses in a CPMG sequence, it is necessary to combine these refocusing pulses with a broadband excitation pulse. When it is not possible to use a short, high amplitude excitation pulse, we show that phase-alternating (PA) excitation pulses are suitable for this purpose. We present a detailed analysis of the underlying spin dynamics of these new pulse sequences and confirm the simulations with experiments. We show that for samples with T1/T2 > 1, the new sequences in grossly inhomogeneous fields do not only generate echoes with an increased amplitude, but also with an increased decay time. Finally, we analyze the diffusion properties and show quantitatively that the broadband sequences have a substantially higher diffusion sensitivity compared with the standard CPMG sequence.

  4. Pulse Distortion in Saturated Fiber Optical Parametric Chirped Pulse Amplification

    DEFF Research Database (Denmark)

    Lali-Dastjerdi, Zohreh; Da Ros, Francesco; Rottwitt, Karsten

    2012-01-01

    Fiber optical parametric chirped pulse amplification is experimentally compared for different chirped pulses in the picosecond regime. The amplified chirped pulses show distortion appearing as pedestals after recompression when the amplifier is operated in saturation.......Fiber optical parametric chirped pulse amplification is experimentally compared for different chirped pulses in the picosecond regime. The amplified chirped pulses show distortion appearing as pedestals after recompression when the amplifier is operated in saturation....

  5. Power pulsing of the CMOS sensor Mimosa 26

    International Nuclear Information System (INIS)

    Kuprash, Oleg

    2013-01-01

    Mimosa 26 is a monolithic active pixel sensor developed by IPHC (Strasbourg) and IRFU (Saclay) as a prototype for the ILC vertex detector studies. The resolution requirements for the ILC tracking detector are very extreme, demanding very low material in the detector, thus only air cooling can be considered. Power consumption has to be reduced as far as possible. The beam structure of the ILC allows the possibility of power pulsing: only for about the 1 ms long bunch train full power is required, and during the 199 ms long pauses between the bunch trains the power can be reduced to a minimum. Not being adapted for the power pulsing, the sensor shows in laboratory tests a good performance under power pulsing. The power pulsing allows to significantly reduce the heating of the chip and divides power consumption approximately by a factor of 6. In this report a summary of power pulsing studies using the digital readout of Mimosa 26 is given. -- Highlights: • First power pulsing studies using digital readout of Mimosa 26 CMOS sensor were done. • Fake hit rates under power pulsing conditions and under normal conditions were compared. • The measurements demonstrate that there is so far no showstopper to operate CMOS pixel sensors in power pulsing mode

  6. Power pulsing of the CMOS sensor Mimosa 26

    Energy Technology Data Exchange (ETDEWEB)

    Kuprash, Oleg, E-mail: oleg.kuprash@desy.de

    2013-12-21

    Mimosa 26 is a monolithic active pixel sensor developed by IPHC (Strasbourg) and IRFU (Saclay) as a prototype for the ILC vertex detector studies. The resolution requirements for the ILC tracking detector are very extreme, demanding very low material in the detector, thus only air cooling can be considered. Power consumption has to be reduced as far as possible. The beam structure of the ILC allows the possibility of power pulsing: only for about the 1 ms long bunch train full power is required, and during the 199 ms long pauses between the bunch trains the power can be reduced to a minimum. Not being adapted for the power pulsing, the sensor shows in laboratory tests a good performance under power pulsing. The power pulsing allows to significantly reduce the heating of the chip and divides power consumption approximately by a factor of 6. In this report a summary of power pulsing studies using the digital readout of Mimosa 26 is given. -- Highlights: • First power pulsing studies using digital readout of Mimosa 26 CMOS sensor were done. • Fake hit rates under power pulsing conditions and under normal conditions were compared. • The measurements demonstrate that there is so far no showstopper to operate CMOS pixel sensors in power pulsing mode.

  7. Optical pulse compression

    International Nuclear Information System (INIS)

    Glass, A.J.

    1975-01-01

    The interest in using large lasers to achieve a very short and intense pulse for generating fusion plasma has provided a strong impetus to reexamine the possibilities of optical pulse compression at high energy. Pulse compression allows one to generate pulses of long duration (minimizing damage problems) and subsequently compress optical pulses to achieve the short pulse duration required for specific applications. The ideal device for carrying out this program has not been developed. Of the two approaches considered, the Gires--Tournois approach is limited by the fact that the bandwidth and compression are intimately related, so that the group delay dispersion times the square of the bandwidth is about unity for all simple Gires--Tournois interferometers. The Treacy grating pair does not suffer from this limitation, but is inefficient because diffraction generally occurs in several orders and is limited by the problem of optical damage to the grating surfaces themselves. Nonlinear and parametric processes were explored. Some pulse compression was achieved by these techniques; however, they are generally difficult to control and are not very efficient. (U.S.)

  8. RF Pulsed Heating

    Energy Technology Data Exchange (ETDEWEB)

    Pritzkau, David P.

    2002-01-03

    RF pulsed heating is a process by which a metal is heated from magnetic fields on its surface due to high-power pulsed RF. When the thermal stresses induced are larger than the elastic limit, microcracks and surface roughening will occur due to cyclic fatigue. Pulsed heating limits the maximum magnetic field on the surface and through it the maximum achievable accelerating gradient in a normal conducting accelerator structure. An experiment using circularly cylindrical cavities operating in the TE{sub 011} mode at a resonant frequency of 11.424 GHz is designed to study pulsed heating on OFE copper, a material commonly used in normal conducting accelerator structures. The high-power pulsed RF is supplied by an X-band klystron capable of outputting 50 MW, 1.5 {micro}s pulses. The test pieces of the cavity are designed to be removable to allow testing of different materials with different surface preparations. A diagnostic tool is developed to measure the temperature rise in the cavity utilizing the dynamic Q change of the resonant mode due to heating. The diagnostic consists of simultaneously exciting a TE{sub 012} mode to steady-state in the cavity at 18 GHz and measuring the change in reflected power as the cavity is heated from high-power pulsed RF. Two experimental runs were completed. One run was executed at a calculated temperature rise of 120 K for 56 x 10{sup 6} pulses. The second run was executed at a calculated temperature rise of 82 K for 86 x 10{sup 6} pulses. Scanning electron microscope pictures show extensive damage occurring in the region of maximum temperature rise on the surface of the test pieces.

  9. Formation of ultrashort pulses from monochromatic XUV radiation via interaction with a medium of IR-dressed He atoms

    Science.gov (United States)

    Akhmedzhanov, Timur; Antonov, Vladimir; Kocharovskaya, Olga

    Trains of high intensity ultrashort XUV pulses could find a lot of applications. Recently, a mechanism of high efficiency formation of a train of XUV pulses from quasi-monochromatic XUV field was suggested. XUV field propagates through the medium of atoms, which are space-time modulated by IR field. The field scattered by modulated atoms contains sidebands of incident XUV field frequency and, for properly chosen parameters, train of ultrashort pulses is formed at the output of the medium. In this contribution, we study formation of ultrashort pulses in the medium of He atoms. Contrary to our recent work, IR field is chosen to be weak enough, so that pulses are formed due to modulation of excited atomic levels, rather than tunnel ionization. The suggested method allows to form train of pulses with high efficiency and can be scaled to He-like ions in order to get even shorter pulses.

  10. Pulse-width discriminators

    International Nuclear Information System (INIS)

    Budyashov, Yu.G.; Grebenyuk, V.M.; Zinov, V.G.

    1978-01-01

    A pulse duration discriminator is described which is intended for processing signals from multilayer scintillators. The basic elements of the scintillator are: an input gate, a current generator, an integrating capacitor, a Schmidt trigger and an anticoincidence circuit. The basic circuit of the discriminator and its time diagrams explaining its operating are given. The discriminator is based on microcircuits. Pulse duration discrimination threshold changes continuously from 20 to 100 ns, while its amplitude threshold changes within 20 to 100 mV. The temperature instability of discrimination thresholds (both in pulse width and in amplitude) is better than 0.1 per cent/deg C

  11. Radio frequency pulse compression

    International Nuclear Information System (INIS)

    Farkas, Z.D.

    1988-12-01

    High gradients require peak powers. One possible way to generate high peak powers is to generate a relatively long pulse at a relatively low power and compress it into a shorter pulse with higher peak power. It is possible to compress before dc to rf conversion as is done for the relativistic klystron or after dc to rf conversion as is done with SLED. In this note only radio frequency pulse compression (RFPC) is considered. Three methods of RFPC will be discussed: SLED, BEC, and REC. 3 refs., 8 figs., 1 tab

  12. High performance pulse generator

    Science.gov (United States)

    Grothaus, Michael G.; Moran, Stuart L.; Hardesty, Leonard W.

    1992-06-01

    The device is a compact Marx-type generator capable of producing a high-voltage burst of pulses having risetimes less than 10 nanoseconds at repetition rates up to 10 kHz. High-pressure hydrogen switches are used as the switching elements to achieve high rep-rate. A small coaxial design provides low inductance and a fast risetime. The device may be used as a high-rep-rate high-voltage trigger generator, or as a high-voltage pulse source capable of producing up to 1 MV pulses at high repetition rates.

  13. DogPulse

    DEFF Research Database (Denmark)

    Skovgaard, Christoffer; Thomsen, Josephine Raun; Verdezoto, Nervo

    2015-01-01

    This paper presents DogPulse, an ambient awareness system to support the coordination of dog walking among family members at home. DogPulse augments a dog collar and leash set to activate an ambient shape-changing lamp and visualize the last time the dog was taken for a walk. The lamp gradually...... changes its form and pulsates its lights in order to keep the family members aware of the dog walking activity. We report the iterative prototyping of DogPulse, its implementation and its preliminary evaluation. Based on our initial findings, we present the limitations and lessons learned as well...

  14. Pulse joining cartridges

    Energy Technology Data Exchange (ETDEWEB)

    Golovashchenko, Sergey Fedorovich; Bonnen, John Joseph Francis

    2017-09-26

    A pulsed joining tool includes a tool body that defines a cavity that receives an inner tubular member and an outer tubular member and a pulse joining cartridge. The tubular members are nested together with the cartridge being disposed around the outer tubular member. The cartridge includes a conductor, such as a wire or foil, that extends around the outer tubular member and is insulated to separate a supply segment from a return segment. A source of stored electrical energy is discharged through the conductor to join the tubular members with an electromagnetic force pulse.

  15. Pulsed energy storage antennas for ionospheric modification

    Directory of Open Access Journals (Sweden)

    R. F. Wuerker

    2005-01-01

    Full Text Available Interesting, "new", very high peak-power pulsed radio frequency (RF antennas have been assembled at the HIPAS Observatory (Alaska, USA and also at the University of California at Los Angeles (UCLA, USA; namely, a pair of quarter wavelength (λ/4 long cylindrical conductors separated by a high voltage spark gap. Such a combination can radiate multi-megawatt RF pulses whenever the spark gap fires. The antenna at HIPAS is 53m long (λ/2 with a central pressurized SF6 spark gap. It is mounted 5 meters (λ/21 above a ground plane. It radiates at 2.85MHz. The two antenna halves are charged to ± high voltages by a Tesla coil. Spark gap voltages of 0.4 MV (at the instant of spark gap closure give peak RF currents of ~1200A which correspond to ~14 MW peak total radiated power, or ~56 MW of Effective Radiated Power (ERP. The RF pulse train is initially square, decaying exponentially in time with Qs of ~50. Two similar but smaller 80-MHz antennas were assembled at UCLA to demonstrate their synchronization with a pulsed laser which fired the spark gaps in the two antennas simultanoeously. These experiments show that one can anticipate a pulsed array of laser synchronized antennas having a coherent Effective Radiated Power (ERP>10GW. One can even reconsider a pulse array radiating at 1.43MHz which corresponds to the electron gyrofrequency in the Earth's magnetic field at ~200km altitude. These "new" pulsed high power antennas are hauntingly similar to the ones used originally by Hertz (1857-1894 during his (1886-1889 seminal verifications of Maxwell's (1864 theory of electrodynamics.

  16. Pulsed energy storage antennas for ionospheric modification

    Directory of Open Access Journals (Sweden)

    R. F. Wuerker

    2005-01-01

    Full Text Available Interesting, "new", very high peak-power pulsed radio frequency (RF antennas have been assembled at the HIPAS Observatory (Alaska, USA and also at the University of California at Los Angeles (UCLA, USA; namely, a pair of quarter wavelength (λ/4 long cylindrical conductors separated by a high voltage spark gap. Such a combination can radiate multi-megawatt RF pulses whenever the spark gap fires. The antenna at HIPAS is 53m long (λ/2 with a central pressurized SF6 spark gap. It is mounted 5 meters (λ/21 above a ground plane. It radiates at 2.85MHz. The two antenna halves are charged to ± high voltages by a Tesla coil. Spark gap voltages of 0.4 MV (at the instant of spark gap closure give peak RF currents of ~1200A which correspond to ~14 MW peak total radiated power, or ~56 MW of Effective Radiated Power (ERP. The RF pulse train is initially square, decaying exponentially in time with Qs of ~50. Two similar but smaller 80-MHz antennas were assembled at UCLA to demonstrate their synchronization with a pulsed laser which fired the spark gaps in the two antennas simultanoeously. These experiments show that one can anticipate a pulsed array of laser synchronized antennas having a coherent Effective Radiated Power (ERP>10GW. One can even reconsider a pulse array radiating at 1.43MHz which corresponds to the electron gyrofrequency in the Earth's magnetic field at ~200km altitude. These "new" pulsed high power antennas are hauntingly similar to the ones used originally by Hertz (1857-1894 during his (1886-1889 seminal verifications of Maxwell's (1864 theory of electrodynamics.

  17. Pulse holographic measurement techniques

    International Nuclear Information System (INIS)

    Kim, Cheol Jung; Baik, Seong Hoon; Hong, Seok Kyung; Kim, Jeong Moog; Kim, Duk Hyun

    1992-01-01

    With the development of laser, remote inspection techniques using laser have been growing on. The inspection and measurement techniques by pulse holography are well-established technique for precise measurement, and widely used in various fields of industry now. In nuclear industry, this technology is practically used because holographic inspection is remote, noncontact, and precise measurement technique. In relation to remote inspection technology in nuclear industry, state-of-the art of pulse HNDT (Holographic non-destructive testing) and holographic measurement techniques are examined. First of all, the fundamental principles as well as practical problems for applications are briefly described. The fields of pulse holography have been divided into the HNDT, flow visualization and distribution study, and other application techniques. Additionally holographic particle study, bubble chamber holography, and applications to other visualization techniques are described. Lastly, the current status for the researches and applications of pulse holography to nuclear industry which are carried out actively in Europe and USA, is described. (Author)

  18. IAE pulsed electrostatic accelerator

    International Nuclear Information System (INIS)

    Afanas'ev, V.P.; Ganzhelyuk, M.L.; Kozlov, L.D.; Koltypin, E.A.; Molchanov, Yu.D.; Otroshchenko, G.A.; Yan'kov, G.B.

    1976-01-01

    The modernized pulse electrostatic accelerator using the klystron ion grouping and the beam interruption system prior to acceleration is described. The accelerator is modernized in order to improve parameters of a current pulse and to decrease the background in the measurement room. The ion beam of needed dimensions is obtained with the help of a high-frequency source and a beam grouping and deflection system. The general view of the beam grouping and deflection system is shown. The ion beam forming process is considered in detail. The modernized electrostatic accelerator permits to obtain a pulse current with a pulse length of 1.5 ns and an amplitude of 1.5 - 2 μA. With the repetition frequency of 2 MHz, the average target current is about 6 μA

  19. Pulsed Lorentz Accelerator

    Data.gov (United States)

    National Aeronautics and Space Administration — The Pulsed Lorentz Accelerator (PLA) is proposed to fill the propulsion gap for 6U and smaller satellites. The primary objective is to demonstrate the basic...

  20. Online measurement method for pulse amplitude in pulsed extraction columns

    International Nuclear Information System (INIS)

    Wang Xinghai; Li Shichang; Chen Jing

    2009-01-01

    Online measurement of pulse amplitude by air purge was studied. The pulse amplitude in a pulsed extraction column was calculated online by measurement of characteristic parameters of the signal's curve. The method can be used for calculation of different pulsed extraction columns. (authors)