Ultrashort X-ray pulse science

International Nuclear Information System (INIS)

Chin, A.H.; Lawrence Berkeley National Lab., CA

1998-01-01

A variety of phenomena involves atomic motion on the femtosecond time-scale. These phenomena have been studied using ultrashort optical pulses, which indirectly probe atomic positions through changes in optical properties. Because x-rays can more directly probe atomic positions, ultrashort x-ray pulses are better suited for the study of ultrafast structural dynamics. One approach towards generating ultrashort x-ray pulses is by 90 o Thomson scattering between terawatt laser pulses and relativistic electrons. Using this technique, the author generated ∼ 300 fs, 30 keV (0.4 (angstrom)) x-ray pulses. These x-ray pulses are absolutely synchronized with ultrashort laser pulses, allowing femtosecond optical pump/x-ray probe experiments to be performed. Using the right-angle Thomson scattering x-ray source, the author performed time-resolved x-ray diffraction studies of laser-perturbated InSb. These experiments revealed a delayed onset of lattice expansion. This delay is due to the energy relaxation from a dense electron-hole plasma to the lattice. The dense electron-hole plasma first undergoes Auger recombination, which reduces the carrier concentration while maintaining energy content. Longitudinal-optic (LO) phonon emission then couples energy to the lattice. LO phonon decay into acoustic phonons, and acoustic phonon propagation then causes the growth of a thermally expanded layer. Source characterization is instrumental in utilizing ultrashort x-ray pulses in time-resolved x-ray spectroscopies. By measurement of the electron beam diameter at the generation point, the pulse duration of the Thomson scattered x-rays is determined. Analysis of the Thomson scattered x-ray beam properties also provides a novel means of electron bunch characterization. Although the pulse duration is inferred for the Thomson scattering x-ray source, direct measurement is required for other x-ray pulse sources. A method based on the laser-assisted photoelectric effect (LAPE) has been

Optical and electrical properties of SnO2 thin films after ultra-short pulsed laser annealing

NARCIS (Netherlands)

Scorticati, D.; Illiberi, A.; Römer, G.R.B.E.; Bor, T.; Ogieglo, W.; Klein Gunnewiek, M.; Lenferink, A.; Otto, C.; Skolski, J.Z.P.; Grob, F.; Lange, D.F. de; Huis in 't Veld, A.J.

2013-01-01

Ultra-short pulsed laser sources, with pulse durations in the ps and fs regime, are commonly exploited for cold ablation. However, operating ultra-short pulsed laser sources at fluence levels well below the ablation threshold allows for fast and selective thermal processing. The latter is especially

International Conference on the Interaction of atoms, molecules and plasmas with intense ultrashort laser pulses. Book of abstracts

International Nuclear Information System (INIS)

2006-01-01

International Conference on the Interaction of atoms, molecules and plasmas with intense ultrashort laser pulses was held in Hungary in 2006. This conference which joined the ULTRA COST activity ('Laser-matter interactions with ultra-short pulses, high-frequency pulses and ultra-intense pulses. From attophysics to petawatt physics') and the XTRA ('Ultrashort XUV Pulses for Time-Resolved and Non-Linear Applications') Marie-Curie Research Training Network, intends to offer a possibility to the members of both of these activities to exchange ideas on recent theoretical and experimental results on the interaction of ultrashort laser pulses with matter giving a broad view from theoretical models to practical and technical applications. Ultrashort laser pulses reaching extra high intensities open new windows to obtain information about molecular and atomic processes. These pulses are even able to penetrate into atomic scalelengths not only by generating particles of ultrahigh energy but also inside the spatial and temporal atomic scalelengths. New regimes of laser-matter interaction were opened in the last decade with an increasing number of laboratories and researchers in these fields. (S.I.)

Thin film surface processing by UltraShort Laser Pulses (USLP)

NARCIS (Netherlands)

Scorticati, D.; Skolski, J.Z.P.; Römer, G.R.B.E.; Huis in 't Veld, A.J.; Workum, M.; Theelen, M.J.; Zeman, M.

2012-01-01

In this work, we studied the feasibility of surface texturing of thin molybdenum layers on a borosilicate glass substrate with Ultra-Short Laser Pulses (USLP). Large areas of regular diffraction gratings were produced consisting of Laserinduced periodic surface structures (LIPSS). A short pulsed

Control of the hyperbolic dispersion of dielectrics by an ultrashort laser pulse

Science.gov (United States)

Zhang, Xiaoqin; Wang, Feng; Zhang, Fengshou; Yao, Yugui

2018-01-01

An idea of controlling hyperbolic dispersion of dielectric materials by an ultrashort laser pulse is proposed. Taking the diamond as a concrete example and using time-dependent density functional theory calculations, we show that the permittivity tensor of the material can be effectively tuned by an ultrashort laser pulse, serving as a transient hyperbolic medium with wide working frequency window. With easily tunable laser parameters, the material can even be switched by reversal of both elliptic and hyperbolic for a particular light frequency. Our result points out a route toward transient hyperbolic materials, and it offers methods to achieve tunable hyperbolic dispersion with great potential for ultrafast device applications.

Selective laser melting of hypereutectic Al-Si40-powder using ultra-short laser pulses

Science.gov (United States)

Ullsperger, T.; Matthäus, G.; Kaden, L.; Engelhardt, H.; Rettenmayr, M.; Risse, S.; Tünnermann, A.; Nolte, S.

2017-12-01

We investigate the use of ultra-short laser pulses for the selective melting of Al-Si40-powder to fabricate complex light-weight structures with wall sizes below 100 μ {m} combined with higher tensile strength and lower thermal expansion coefficient in comparison to standard Al-Si alloys. During the cooling process using conventional techniques, large primary silicon particles are formed which impairs the mechanical and thermal properties. We demonstrate that these limitations can be overcome using ultra-short laser pulses enabling the rapid heating and cooling in a non-thermal equilibrium process. We analyze the morphology characteristics and micro-structures of single tracks and thin-walled structures depending on pulse energy, repetition rate and scanning velocity utilizing pulses with a duration of 500 {fs} at a wavelength of 1030 {nm}. The possibility to specifically change and optimize the microstructure is shown.

Optical and electrical properties of SnO2 thin films after ultra-short pulsed laser annealing

OpenAIRE

Scorticati, D.; Illiberi, A.; Römer, G.R.B.E.; Bor, T.; Ogieglo, W.; Klein Gunnewiek, M.; Lenferink, A.; Otto, C.; Skolski, J.Z.P.; Grob, F.; Lange, D.F. de; Huis in 't Veld, A.J.

2013-01-01

Ultra-short pulsed laser sources, with pulse durations in the ps and fs regime, are commonly exploited for cold ablation. However, operating ultra-short pulsed laser sources at fluence levels well below the ablation threshold allows for fast and selective thermal processing. The latter is especially advantageous for the processing of thin films. A precise control of the heat affected zone, as small as tens of nanometers, depending on the material and laser conditions, can be achieved. It enab...

Ultrashort-pulse laser excitation and damage of dielectric materials

DEFF Research Database (Denmark)

Haahr-Lillevang, Lasse; Balling, Peter

2015-01-01

Ultrashort-pulse laser excitation of dielectrics is an intricate problem due to the strong coupling between the rapidly changing material properties and the light. In the present paper, details of a model based on a multiple-rate-equation description of the conduction band are provided. The model...

Nonlinear propagation of ultrashort laser pulses in transparent media

International Nuclear Information System (INIS)

Vincotte, A.

2006-10-01

We present different aspects of the propagation of ultrashort laser pulses in transparent media. First, we derive the propagation equations starting from the Maxwell equations. We remind of the main physical phenomena undergone by ultrashort and powerful laser pulses. First self-focusing occurs, owing to the Kerr response of the medium. This self-focusing is stopped by plasma generation from the laser-induced ionization of the ambient atoms. The propagation of the wave generates a super-continuum through self-phase modulation. We recall the main results concerning the simple and multiple filamentation of an intense wave, induced by the beam inhomogeneities and which take place as soon as the beam power is above critical. In a second part, we investigate the influence of high-order nonlinearities on the propagation of the beam and especially on its filamentation pattern. To control the multi-filamentation process, we investigate in a third part the propagation of beams with special designs, namely; Gradient- and vortex-shaped beams. We justify the robustness of this latter kind of optical objects. Eventually, we investigate multi-filamentation patterns of femtosecond pulses in a fog tube and in cells of ethanol doped with coumarin, for different beam configurations. (author)

Plasma discreteness effects in the presence of an intense, ultrashort laser pulse

Energy Technology Data Exchange (ETDEWEB)

Savchenko, V.I.; Fisch, N.J.

1996-03-01

Discrete effects of the plasma irradiated by an ultrashort, intense laser pulse are investigated. Although, for most plasmas of interest, the damping of the laser pulse is due to collective plasma effects, in certain regimes the energy absorbed in the plasma microfields can be important. A scattering matrix is derived for an electron scattering off an ion in the presence of an intense laser field.

Plasma discreteness effects in the presence of an intense, ultrashort laser pulse

International Nuclear Information System (INIS)

Savchenko, V.I.; Fisch, N.J.

1996-03-01

Discrete effects of the plasma irradiated by an ultrashort, intense laser pulse are investigated. Although, for most plasmas of interest, the damping of the laser pulse is due to collective plasma effects, in certain regimes the energy absorbed in the plasma microfields can be important. A scattering matrix is derived for an electron scattering off an ion in the presence of an intense laser field

Ultrashort x-ray pulse generation by nonlinear Thomson scattering of a relativistic electron with an intense circularly polarized laser pulse

Directory of Open Access Journals (Sweden)

F. Liu

2012-07-01

Full Text Available The nonlinear Thomson scattering of a relativistic electron with an intense laser pulse is calculated numerically. The results show that an ultrashort x-ray pulse can be generated by an electron with an initial energy of 5 MeV propagating across a circularly polarized laser pulse with a duration of 8 femtosecond and an intensity of about 1.1×10^{21}  W/cm^{2}, when the detection direction is perpendicular to the propagation directions of both the electron and the laser beam. The optimal values of the carrier-envelop phase and the intensity of the laser pulse for the generation of a single ultrashort x-ray pulse are obtained and verified by our calculations of the radiation characteristics.

Printed organic smart devices characterized by ultra-short laser pulses

DEFF Research Database (Denmark)

Pastorelli, Francesco

Resume: In this study, we demonstrate that nonlinear optical microscopy is a promising technique to characterize organic printed electronics. Using ultrashort laser pulses we stimulate two-photon absorption in a roll coated polymer semiconductor and map the resulting two-photon induced...

Study of laser pulses propagation through an ultrashort pulse amplifying systems for the development of an Offner temporal stretcher

International Nuclear Information System (INIS)

Cordeiro, Thiago da Silva

2009-01-01

The study of laser pulses propagation through an ultrashort pulses amplifying system containing dispersive and spectral modifying media was performed. The study emphasis was the development of an ultrashort pulse stretcher to replace the one inside a hybrid Ti:Sapphire/Cr:LiSAF CPA system operating at the Center for Lasers and Applications at IPEN/CNEN-SP. A spherical aberration free Offner stretcher was theoretically studied, aiming to obtain a stretching ratio larger than the one available in our system. The influence of the phase components in the amplified pulse final duration was also studied, and the bandwidth limiting elements of the system in operation were mapped, with the purpose of determining the conditions under which a new stretcher should be implemented. Based on the actual measurements, computing routines were implemented in order to determine the consequences of an ultrashort pulse travelling through a bandwidth limiting component. (author)

Fragmentation dynamics of molecular hydrogen in strong ultrashort laser pulses

International Nuclear Information System (INIS)

Rudenko, A; Feuerstein, B; Zrost, K; Jesus, V L B de; Ergler, T; Dimopoulou, C; Schroeter, C D; Moshammer, R; Ullrich, J

2005-01-01

We present the results of a systematic experimental study of dissociation and Coulomb explosion of molecular hydrogen induced by intense ultrashort (7-25 fs) laser pulses. Using coincident recoil-ion momentum spectroscopy we can distinguish the contributions from dissociation and double ionization even if they result in the same kinetic energies of the fragments. The dynamics of all fragmentation channels drastically depends on the pulse duration, and for 7 fs pulses becomes extremely sensitive to the pulse shape

Ionization of molecular hydrogen in ultrashort intense laser pulses

Energy Technology Data Exchange (ETDEWEB)

Vanne, Yulian V.

2010-03-18

A novel ab initio numerical approach is developed and applied that solves the time-dependent Schroedinger equation describing two-electron diatomic molecules (e.g. molecular hydrogen) exposed to an intense ultrashort laser pulse. The method is based on the fixed-nuclei and the non-relativistic dipole approximations and aims to accurately describe both correlated electrons in full dimensionality. The method is applicable for a wide range of the laser pulse parameters and is able to describe both few-photon and many-photon single ionization processes, also in a non-perturbative regime. A key advantage of the method is its ability to treat the strong-field response of the molecules with arbitrary orientation of the molecular axis with respect to the linear-polarized laser field. Thus, this work reports on the first successful orientation-dependent analysis of the multiphoton ionization of H{sub 2} performed by means of a full-dimensional numerical treatment. Besides the investigation of few-photon regime, an extensive numerical study of the ionization by ultrashort frequency-doubled Ti:sapphire laser pulses (400 nm) is presented. Performing a series of calculations for different internuclear separations, the total ionization yields of H{sub 2} and D{sub 2} in their ground vibrational states are obtained for both parallel and perpendicular orientations. A series of calculations for 800 nm laser pulses are used to test a popular simple interference model. Besides the discussion of the ab initio numerical method, this work considers different aspects related to the application of the strong-field approximation (SFA) for investigation of a strong-field response of an atomic and molecular system. Thus, a deep analysis of the gauge problem of SFA is performed and the quasistatic limit of the velocity-gauge SFA ionization rates is derived. The applications of the length-gauge SFA are examined and a recently proposed generalized Keldysh theory is criticized. (orig.)

Ionization of molecular hydrogen in ultrashort intense laser pulses

International Nuclear Information System (INIS)

Vanne, Yulian V.

2010-01-01

A novel ab initio numerical approach is developed and applied that solves the time-dependent Schroedinger equation describing two-electron diatomic molecules (e.g. molecular hydrogen) exposed to an intense ultrashort laser pulse. The method is based on the fixed-nuclei and the non-relativistic dipole approximations and aims to accurately describe both correlated electrons in full dimensionality. The method is applicable for a wide range of the laser pulse parameters and is able to describe both few-photon and many-photon single ionization processes, also in a non-perturbative regime. A key advantage of the method is its ability to treat the strong-field response of the molecules with arbitrary orientation of the molecular axis with respect to the linear-polarized laser field. Thus, this work reports on the first successful orientation-dependent analysis of the multiphoton ionization of H 2 performed by means of a full-dimensional numerical treatment. Besides the investigation of few-photon regime, an extensive numerical study of the ionization by ultrashort frequency-doubled Ti:sapphire laser pulses (400 nm) is presented. Performing a series of calculations for different internuclear separations, the total ionization yields of H 2 and D 2 in their ground vibrational states are obtained for both parallel and perpendicular orientations. A series of calculations for 800 nm laser pulses are used to test a popular simple interference model. Besides the discussion of the ab initio numerical method, this work considers different aspects related to the application of the strong-field approximation (SFA) for investigation of a strong-field response of an atomic and molecular system. Thus, a deep analysis of the gauge problem of SFA is performed and the quasistatic limit of the velocity-gauge SFA ionization rates is derived. The applications of the length-gauge SFA are examined and a recently proposed generalized Keldysh theory is criticized. (orig.)

Heat wave propagation in a thin film irradiated by ultra-short laser pulses

International Nuclear Information System (INIS)

Yoo, Jae Gwon; Kim, Cheol Jung; Lim, C. H.

2004-01-01

A thermal wave solution of a hyperbolic heat conduction equation in a thin film is developed on the basis of the Green's function formalism. Numerical computations are carried out to investigate the temperature response and the propagation of the thermal wave inside a thin film due to a heat pulse generated by ultra-short laser pulses with various laser pulse durations and thickness of the film

Ultrashort pulse laser processing of hard tissue, dental restoration materials, and biocompatibles

Science.gov (United States)

Yousif, A.; Strassl, M.; Beer, F.; Verhagen, L.; Wittschier, M.; Wintner, E.

2007-07-01

During the last few years, ultra-short laser pulses have proven their potential for application in medical tissue treatment in many ways. In hard tissue ablation, their aptitude for material ablation with negligible collateral damage provides many advantages. Especially teeth representing an anatomically and physiologically very special region with less blood circulation and lower healing rates than other tissues require most careful treatment. Hence, overheating of the pulp and induction of microcracks are some of the most problematic issues in dental preparation. Up till now it was shown by many authors that the application of picosecond or femtosecond pulses allows to perform ablation with very low damaging potential also fitting to the physiological requirements indicated. Beside the short interaction time with the irradiated matter, scanning of the ultra-short pulse trains turned out to be crucial for ablating cavities of the required quality. One main reason for this can be seen in the fact that during scanning the time period between two subsequent pulses incident on the same spot is so much extended that no heat accumulation effects occur and each pulse can be treated as a first one with respect to its local impact. Extension of this advantageous technique to biocompatible materials, i.e. in this case dental restoration materials and titanium plasma-sprayed implants, is just a matter of consequence. Recently published results on composites fit well with earlier data on dental hard tissue. In case of plaque which has to be removed from implants, it turns out that removal of at least the calcified version is harder than tissue removal. Therefore, besides ultra-short lasers, also Diode and Neodymium lasers, in cw and pulsed modes, have been studied with respect to plaque removal and sterilization. The temperature increase during laser exposure has been experimentally evaluated in parallel.

Interaction of high power ultrashort laser pulses with plasmas

International Nuclear Information System (INIS)

Geissler, M.

2000-12-01

The invention of short laser-pulses has opened a vast application range from testing ultra high-speed semiconductor devices to precision material processing, from triggering and tracing chemical reactions to sophisticated surgical applications in opthalmology and neurosurgery. In physical science, ultrashort light pulses enable researchers to follow ultrafast relaxation processes in the microcosm on time scale never before accessible and study light-matter-interactions at unprecedented intensity levels. The aim of this thesis is to investigate the interaction of ultrashort high power laser pulses with plasmas for a broad intensity range. First the ionization of atoms with intense laser fields is investigated. For sufficient strong and low frequent laser pulses, electrons can be removed from the core by a tunnel process through a potential barrier formed by the electric field of the laser. This mechanism is described by a well-established theory, but the interaction of few-cycle laser pulses with atoms can lead to regimes where the tunnel theory loses its validity. This regime is investigated and a new description of the ionization is found. Although the ionization plays a major role in many high-energy laser processes, there exist no simple and complete model for the evolution of laser pulses in field-ionizing media. A new propagation equation and the polarization response for field-ionizing media are presented and the results are compared with experimental data. Further the interaction of high power laser radiation with atoms result in nonlinear response of the electrons. The spectrum of this induced nonlinear dipole moment reaches beyond visible wavelengths into the x-ray regime. This effect is known as high harmonic generation (HHG) and is a promising tool for the generation of coherent shot wavelength radiation, but the conversions are still not efficient enough for most practical applications. Phase matching schemes to overcome the limitation are discussed

Annealing of SnO2 thin films by ultra-short laser pulses

NARCIS (Netherlands)

Scorticati, D.; Illiberi, A.; Bor, T.; Eijt, S.W.H.; Schut, H.; Römer, G.R.B.E.; Lange, D.F. de; Huis In't Veld, A.J.

2014-01-01

Post-deposition annealing by ultra-short laser pulses can modify the optical properties of SnO2 thin films by means of thermal processing. Industrial grade SnO2 films exhibited improved optical properties after picosecond laser irradiation, at the expense of a slightly increased sheet resistance

Optical reprogramming with ultrashort femtosecond laser pulses

Science.gov (United States)

Uchugonova, Aisada; Breunig, Hans G.; Batista, Ana; König, Karsten

2015-03-01

The use of sub-15 femtosecond laser pulses in stem cell research is explored with particular emphasis on the optical reprogramming of somatic cells. The reprogramming of somatic cells into induced pluripotent stem (iPS) cells can be evoked through the ectopic expression of defined transcription factors. Conventional approaches utilize retro/lenti-viruses to deliver genes/transcription factors as well as to facilitate the integration of transcription factors into that of the host genome. However, the use of viruses may result in insertional mutations caused by the random integration of genes and as a result, this may limit the use within clinical applications due to the risk of the formation of cancer. In this study, a new approach is demonstrated in realizing non-viral reprogramming through the use of ultrashort laser pulses, to introduce transcription factors into the cell so as to generate iPS cells.

Modification of transparent materials with ultrashort laser pulses: What is energetically and mechanically meaningful?

Energy Technology Data Exchange (ETDEWEB)

Bulgakova, Nadezhda M., E-mail: nadezhda.bulgakova@hilase.cz [HiLASE Centre, Institute of Physics ASCR, Za Radnicí 828, 25241 Dolní Břežany (Czech Republic); Institute of Thermophysics SB RAS, 1 Lavrentyev Ave., 630090 Novosibirsk (Russian Federation); Zhukov, Vladimir P. [Institute of Computational Technologies SB RAS, 6 Lavrentyev Ave., 630090 Novosibirsk (Russian Federation); Novosibirsk State Technical University, 20 Karl Marx Ave., 630073, Novosibirsk (Russian Federation); Sonina, Svetlana V. [Novosibirsk State University, 1 Koptuga Ave., 630090 Novosibirsk (Russian Federation); Meshcheryakov, Yuri P. [Design and Technology Branch of Lavrentyev Institute of Hydrodynamics SB RAS, Tereshkovoi street 29, 630090 Novosibirsk (Russian Federation)

2015-12-21

A comprehensive analysis of laser-induced modification of bulk glass by single ultrashort laser pulses is presented which is based on combination of optical Maxwell-based modeling with thermoelastoplastic simulations of post-irradiation behavior of matter. A controversial question on free electron density generated inside bulk glass by ultrashort laser pulses in modification regimes is addressed on energy balance grounds. Spatiotemporal dynamics of laser beam propagation in fused silica have been elucidated for the regimes used for direct laser writing in bulk glass. 3D thermoelastoplastic modeling of material relocation dynamics under laser-induced stresses has been performed up to the microsecond timescale when all motions in the material decay. The final modification structure is found to be imprinted into material matrix already at sub-nanosecond timescale. Modeling results agree well with available experimental data on laser light transmission through the sample and the final modification structure.

Electron emission from insulator surfaces by ultra-short laser pulses

Energy Technology Data Exchange (ETDEWEB)

Acuna, M; Gravielle, M S, E-mail: mario@iafe.uba.a, E-mail: msilvia@iafe.uba.a [Institutes de AstronomIa y Fisica del Espacio, Casilla de Correo 67, Sucursal 28, 1428 Buenos Aires (Argentina)

2009-11-01

Photoelectron emission from insulator surfaces induced by ultra-short laser pulses is studied within a time-dependent distorted wave method. The proposed approach combines the Volkov phase, which takes into account the laser interaction, with a simple representation of the unperturbed surface states, given by the Tight-binding method. The model is applied to evaluate the photoelectron emission from a LiF(001) surface, finding effects of interference produced by the crystal lattice.

Dynamics of interaction of ultrashort laser pulses with solid targets

International Nuclear Information System (INIS)

Cang Yu; Wang Wei; Zhang Jie

2001-01-01

Using Saha equation, a simple model is proposed for the dynamics of interaction between ultrashort laser pulses and solid targets. An adiabatic expansion model is adopted to study the expansion phase after the heating phase. Temporal evolvement of the dynamics of the interaction is obtained, from which the electron temperature, density, ionization balances can be determined

Self-oscillations in cw solid-state ultrashort-pulse-generating lasers with mode locking by self-focusing

International Nuclear Information System (INIS)

Kalashnikov, V L; Krimer, D O; Mejid, F; Poloiko, I G; Mikhailov, V P

1999-01-01

Steady-state and transient regimes of ultrashort pulse generation are studied for cw solid-state lasers with mode locking by self-focusing. It is shown that the control parameter, which governs the nature of lasing, is the relationship between self-phase-modulation and the saturation intensity of an efficient shutter, induced by the Kerr self-focusing. Numerical modelling based on mapping the parameters of a quasi-soliton ultrashort pulse, considered in the aberration-free approximation, yields results in good agreement with experiments. (control of laser radiation parameters)

Electron Hole Plasma in Solids Induced by Ultrashort XUV Laser Pulses

International Nuclear Information System (INIS)

Rethfeld, B.; Medvedev, N.

2013-01-01

Irradiation of solids with ultrashort XUV laser pulses leads to an excitation of electrons from the valence band and deeper shells to the conduction band leading to a nonequilibrium highly energetic electron hole plasma. We investigate the transient electron dynamics in a solid semiconductor and metal (silicon and aluminum, respectively) under irradiation with a femtosecond VUV to XUV laser pulse as used in experiments with the Free Electron Laser FLASH at DESY in Hamburg, Germany. Applying the Asymptotical Trajectory Monte-Carlo technique, we obtain the transient energy distribution of the excited and ionized electrons within the solid. Photon absorption by electrons in different bands and secondary excitation and ionization processes are simulated event by event. The method was extended in order to take into account the electronic band structure and Pauli's principle for electrons in the conduction band. In this talk we review our results on the dynamics of the transient electron-hole plasma, in particular its transient density and energy distribution in dependence on laser and material parameters. For semiconductors we introduce the concept of an ''effective energy gap'' for collective electronic excitation, which can be applied to estimate the free electron density after high-intensity ultrashort XUV laser pulse irradiation. For aluminum we demonstrate that the electronic spectra depend on the relaxation kinetics of the excited electronic subsystem. Experimentally observed spectra of emitted photons from irradiated aluminum can be explained well with our results. (author)

On the surface topography of ultrashort laser pulse treated steel surfaces

NARCIS (Netherlands)

Obona, J. Vincenc; Ocelik, V.; Skolski, J. Z. P.; Mitko, V. S.; Romer, G. R. B. E.; in't Veld, A. J. Huis; De Hosson, J. Th M.; Römer, G.R.B.E.; Huis in’t Veld, A.J.

2011-01-01

This paper concentrates on observations of the surface topography by scanning electron microscopy (SEM) on alloyed and stainless steels samples treated by ultrashort laser pulses with duration of 210 fs and 6.7 ps. Globular-like and jet-like objects were found depending on the various levels of the

On the surface topography of ultrashort laser pulse treated steel surface

NARCIS (Netherlands)

Vincenc Obona, J.; Ocelik, V.; Skolski, J.Z.P.; Mitko, V.S.; Mitko, S.; Römer, Gerardus Richardus, Bernardus, Engelina; Huis in 't Veld, Bert; de Hosson, J.Th.M.

2011-01-01

This paper concentrates on observations of the surface topography by scanning electron microscopy (SEM) on alloyed and stainless steels samples treated by ultrashort laser pulses with duration of 210 fs and 6.7 ps. Globular-like and jet-like objects were found depending on the various levels of the

Ultrashort pulse energy distribution for propulsion in space

Science.gov (United States)

Bergstue, Grant Jared

This thesis effort focuses on the development of a novel, space-based ultrashort pulse transmission system for spacecraft. The goals of this research include: (1) ultrashort pulse transmission strategies for maximizing safety and efficiency; (2) optical transmission system requirements; (3) general system requirements including control techniques for stabilization; (4) optical system requirements for achieving effective ablative propulsion at the receiving spacecraft; and (5) ultrashort pulse transmission capabilities required for future missions in space. A key element of the research is the multiplexing device required for aligning the ultrashort pulses from multiple laser sources along a common optical axis for transmission. This strategy enables access to the higher average and peak powers required for useful missions in space.

Plasma lenses for ultrashort multi-petawatt laser pulses

Energy Technology Data Exchange (ETDEWEB)

Palastro, J. P.; Gordon, D.; Hafizi, B.; Johnson, L. A.; Peñano, J.; Hubbard, R. F.; Helle, M.; Kaganovich, D. [Naval Research Laboratory, Washington DC 20375-5346 (United States)

2015-12-15

An ideal plasma lens can provide the focusing power of a small f-number, solid-state focusing optic at a fraction of the diameter. An ideal plasma lens, however, relies on a steady-state, linear laser pulse-plasma interaction. Ultrashort multi-petawatt (MPW) pulses possess broad bandwidths and extreme intensities, and, as a result, their interaction with the plasma lens is neither steady state nor linear. Here, we examine nonlinear and time-dependent modifications to plasma lens focusing, and show that these result in chromatic and phase aberrations and amplitude distortion. We find that a plasma lens can provide enhanced focusing for 30 fs pulses with peak power up to ∼1 PW. The performance degrades through the MPW regime, until finally a focusing penalty is incurred at ∼10 PW.

On the surface topography of ultrashort laser pulse treated steel surfaces

International Nuclear Information System (INIS)

Vincenc Obona, J.; Ocelík, V.; Skolski, J.Z.P.; Mitko, V.S.; Römer, G.R.B.E.; Huis in’t Veld, A.J.; De Hosson, J.Th.M.

2011-01-01

This paper concentrates on observations of the surface topography by scanning electron microscopy (SEM) on alloyed and stainless steels samples treated by ultrashort laser pulses with duration of 210 fs and 6.7 ps. Globular-like and jet-like objects were found depending on the various levels of the fluence applied. It is shown that these features appear due to solid-liquid and liquid-gas transitions within surface layer irradiated by intense laser light. The observations are confronted to the theory of short-pulsed laser light-matter interactions, including interference, excitation of electrons, electron-phonon coupling as well as subsequent ablation. It is shown that the orientation of small ripples does not always depend on the direction of the polarization of laser light.

Multi-Chromatic Ultrashort Pulse Filamentation and Bulk Modification in Dielectrics

Science.gov (United States)

2016-05-05

AFRL-AFOSR-VA-TR-2016-0194 Multi- Chromatic Ultrashort Pulse Filamentation and Bulk Modification in Dielectrics Jeremy Gulley KENNESAW STATE...Jan 2016 4. TITLE AND SUBTITLE Multi- chromatic Ultrashort Pulse Filamentation and Bulk Modification in Dielectrics 5a. CONTRACT NUMBER 5b. GRANT...in, and modification of, dielectric solids by multi- chromatic ultrashort laser pulses. It was a theoretical effort to develop models of multi

Chromium carbide thin films deposited by ultra-short pulse laser deposition

International Nuclear Information System (INIS)

Teghil, R.; Santagata, A.; De Bonis, A.; Galasso, A.; Villani, P.

2009-01-01

Pulsed laser deposition performed by a laser with a pulse duration of 250 fs has been used to deposit films from a Cr 3 C 2 target. Due to the different processes involved in the laser ablation when it is performed by an ultra-short pulse source instead of a conventional short pulse one, it has been possible to obtain in vacuum films containing only one type of carbide, Cr 3 C 2 , as shown by X-ray photoelectron spectroscopy. On the other hand, Cr 3 C 2 is not the only component of the films, since a large amount of amorphous carbon is also present. The films, deposited at room temperature, are amorphous and seem to be formed by the coalescence of a large number of particles with nanometric size. The film composition can be explained in terms of thermal evaporation from particles ejected from the target.

Nonlinear Thomson scattering of a relativistically strong tightly focused ultrashort laser pulse

Energy Technology Data Exchange (ETDEWEB)

Vais, O. E.; Bochkarev, S. G., E-mail: bochkar@sci.lebedev.ru; Bychenkov, V. Yu. [Russian Academy of Sciences, Lebedev Physical Institute (Russian Federation)

2016-09-15

The problem of nonlinear Thomson scattering of a relativistically strong linearly polarized ultrashort laser pulse tightly focused into a spot with a diameter of D{sub F} ≳ λ (where λ is the laser wavelength) is solved. The energy, spectral, and angular distributions of radiation generated due to Thomson scattering from test electrons located in the focal region are found. The characteristics of scattered radiation are studied as functions of the tightness of laser focusing and the initial position of test particles relative to the center of the focal region for a given laser pulse energy. It is demonstrated that the ultratight focusing is not optimal for obtaining the brightest and hardest source of secondary electromagnetic radiation. The hardest and shortest radiation pulse is generated when the beam waist diameter is ≃10λ.

Spectral coherent combination of ultrashort pulses

International Nuclear Information System (INIS)

Ursescu, D.; Banici, R.; Ionel, L.; Rusen, L.; Sandel, S.; Blanaru, C.

2010-01-01

Complete text of publication follows. The coherent beam combination was chosen in several laser systems, including ELI, as a solution to increase the final attainable intensity. However, the coherent beam combination it is also a difficult technique while it has to combine coherently in space and in time several beams amplified in different laser chains. That means in particular that the beams should be in phase in every point of the amplified beam so the spatial beam profiling techniques have to be mastered with high accuracy for all the combined beams. Here it is proposed an alternative coherent beam combination than the use of identical ultrashort pulses. The idea is to spectrally combine laser pulses with complementary spectra. Collinear and non-collinear approaches have been modelled. Ongoing experimental development, including the demonstration of the rephasing for two spectrally complementary ultrashort pulses will be presented. Acknowledgements. The research leading to these results has received funding from the EC's Seventh Framework Programme (LASERLAB-EUROPE, grant agreement no. 228334).

Nonlinear scattering in hard tissue studied with ultrashort laser pulses

International Nuclear Information System (INIS)

Eichler, J.; Kim, B.M.

2002-01-01

The back-scattered spectrum of ultrashort laser pulses (800 nm, 0.2 ps) was studied in human dental and other hard tissues in vitro below the ablation threshold. Frequency doubled radiation (SHG), frequency tripled radiation and two-photon fluorescence were detected. The relative yield for these processes was measured for various pulse energies. The dependence of the SHG signal on probe thickness was determined in forward and back scattering geometry. SHG is sensitive to linear polarization of the incident laser radiation. SHG in human teeth was studied in vitro showing larger signals in dentin than in cementum and enamel. In carious areas no SHG signal could be detected. Possible applications of higher harmonic radiation for diagnostics and microscopy are discussed. (orig.)

Plasma luminescence feedback control system for precise ultrashort pulse laser tissue ablation

Science.gov (United States)

Kim, Beop-Min; Feit, Michael D.; Rubenchik, Alexander M.; Gold, David M.; Darrow, Christopher B.; Marion, John E., II; Da Silva, Luiz B.

1998-05-01

Plasma luminescence spectroscopy was used for precise ablation of bone tissue without damaging nearby soft tissue using an ultrashort pulse laser. Strong contrast of the luminescence spectra between bone marrow and spinal cord provided the real time feedback control so bone tissue is selectively ablated while preserving the spinal cord.

Laser mass spectrometry of chemical warfare agents using ultrashort laser pulses

International Nuclear Information System (INIS)

Weickhardt, C.; Grun, C.; Grotemeyer, J.

1998-01-01

Fast relaxation processes in excited molecules such as IC, ISC, and fragmentation are observed in many environmentally and technically relevant substances. They cause severe problems to resonance ionization mass spectrometry because they reduce the ionization yield and lead to mass spectra which do not allow the identification of the compound. By the use of ultrashort laser pulses these problems can be overcome and the advantages of REMPI over conventional ionization techniques in mass spectrometry can be regained. This is demonstrated using soil samples contaminated with a chemical warfare agent

Interaction of ultrashort laser pulses and silicon solar cells under short circuit conditions

Energy Technology Data Exchange (ETDEWEB)

Mundus, M., E-mail: markus.mundus@ise.fraunhofer.de; Giesecke, J. A.; Fischer, P.; Hohl-Ebinger, J.; Warta, W. [Fraunhofer Institute for Solar Energy Systems (ISE), Heidenhofstraße 2, 79110 Freiburg (Germany)

2015-02-28

Ultrashort pulse lasers are promising tools for numerous measurement purposes. Among other benefits their high peak powers allow for efficient generation of wavelengths in broad spectral ranges and at spectral powers that are orders of magnitude higher than in conventional light sources. Very recently this has been exploited for the establishment of sophisticated measurement facilities for electrical characterization of photovoltaic (PV) devices. As the high peak powers of ultrashort pulses promote nonlinear optical effects they might also give rise to nonlinear interactions with the devices under test that possibly manipulate the measurement outcome. In this paper, we present a comprehensive theoretical and experimental study of the nonlinearities affecting short circuit current (I{sub SC}) measurements of silicon (Si) solar cells. We derive a set of coupled differential equations describing the radiation-device interaction and discuss the nonlinearities incorporated in those. By a semi-analytical approach introducing a quasi-steady-state approximation and integrating a Green's function we solve the system of equations and obtain simulated I{sub SC} values. We validate the theoretical model by I{sub SC} ratios obtained from a double ring resonator setup capable for reproducible generation of various ultrashort pulse trains. Finally, we apply the model to conduct the most prominent comparison of I{sub SC} generated by ultrashort pulses versus continuous illumination. We conclude by the important finding that the nonlinearities induced by ultrashort pulses are negligible for the most common I{sub SC} measurements. However, we also find that more specialized measurements (e.g., of concentrating PV or Si-multijunction devices as well as highly localized electrical characterizations) will be biased by two-photon-absorption distorting the I{sub SC} measurement.

Influence of dispersion stretching of ultrashort UV laser pulse on the critical power for self-focusing

Science.gov (United States)

Ionin, A. A.; Mokrousova, D. V.; Piterimov, D. A.; Seleznev, L. V.; Sinitsyn, D. V.; Sunchugasheva, E. S.

2018-04-01

The critical power for self-focusing in air for ultrashort ultraviolet laser pulses, stretched due to dispersion from 90 to 730 fs, was experimentally measured. It was shown that the pulse duration enhancement due to its propagation in condensed media leads to an almost linear decrease in the critical power for self-focusing. It was also observed that when the pulse peak power exceeds the critical one, the maximum of linear plasma distribution along the ultraviolet laser filament does not shift in the direction opposite to the laser pulse propagation, as observed for infrared laser filaments, but remains at the geometrical focus.

Ultra-short laser pulse ablation using shear-force feedback: Femtosecond laser induced breakdown spectroscopy feasibility study

International Nuclear Information System (INIS)

Samek, Ota; Kurowski, Andre; Kittel, Silke; Kukhlevsky, Sergei; Hergenroeder, Roland

2005-01-01

This work reports on a feasibility study of proximity ablation using femtosecond pulses. Ultra-short pulses were launched to a bare tapered optical fiber and delivered to the sample. The tip-sample distance was controlled by means of shear-force feedback. Consequently, ablation craters with submicrometer dimensions were obtained. Potential analytical applications for Laser Induced Breakdown Spectroscopy (LIBS) technique, such as e.g. inclusions in steel or bio cells, are suggested

Axisymmetric modeling of ultrashort-pulse laser interactions with thin metal film

Directory of Open Access Journals (Sweden)

E. Majchrzak

2011-10-01

Full Text Available The hyperbolic two-temperature model is used in order to describe the heat propagation in metal film subjected to an ultrashort-pulse laser heating. An axisymmetric heat soureceewith Gaussian temporeal and spatial distributions has been taken into account. At the stage of numerical computations the finite difference method is used. In the final part of the paper the examples of computations are shown.

Ultra-short laser pulses: review of the 3. physics talks, September 17-18, 1998

International Nuclear Information System (INIS)

Lemoine, P.

1999-01-01

This book deals with the operation of lasers with ultra-short pulses and with the laser beam-matter interaction. The applications in concern are: the acceleration of particles, the production of X-ray or photon sources, the micro-machining, the fast ignition in thermonuclear fusion, the production of thin films and the surgery of cornea. (J.S.)

Fabrication of Nb/Pb structures through ultrashort pulsed laser deposition

Energy Technology Data Exchange (ETDEWEB)

Gontad, Francisco; Lorusso, Antonella, E-mail: antonella.lorusso@le.infn.it; Perrone, Alessio [Dipartimento di Matematica e Fisica “E. De Giorgi,” Università del Salento and Istituto Nazionale di Fisica Nucleare, 73100 Lecce (Italy); Klini, Argyro; Fotakis, Costas [Institute of Electronic Structure and Laser (IESL), Foundation for Research and Technology-Hellas (FORTH), 100 N. Plastira St., GR 70013 Heraklion, Crete (Greece); Broitman, Esteban [Thin Film Physics Division, IFM, Linköping University, 581-83 Linköping (Sweden)

2016-07-15

This work reports the fabrication of Nb/Pb structures with an application as photocathode devices. The use of relatively low energy densities for the ablation of Nb with ultrashort pulses favors the reduction of droplets during the growth of the film. However, the use of laser fluences in this ablation regime results in a consequent reduction in the average deposition rate. On the other hand, despite the low deposition rate, the films present a superior adherence to the substrate and an excellent coverage of the irregular substrate surface, avoiding the appearance of voids or discontinuities on the film surface. Moreover, the low energy densities used for the ablation favor the growth of nanocrystalline films with a similar crystalline structure to the bulk material. Therefore, the use of low ablation energy densities with ultrashort pulses for the deposition of the Nb thin films allows the growth of very adherent and nanocrystalline films with adequate properties for the fabrication of Nb/Pb structures to be included in superconducting radiofrequency cavities.

Yb3+:Sr3Y2(BO3)4: A potential ultrashort pulse laser crystal

International Nuclear Information System (INIS)

Sun, Shijia; Xu, Jinlong; Wei, Qi; Lou, Fei; Huang, Yisheng; Yuan, Feifei; Zhang, Lizhen; Lin, Zhoubin; He, Jingliang; Wang, Guofu

2015-01-01

Highlights: • A Yb 3+ :Sr 3 Y 2 (BO 3 ) 4 crystal was grown successfully by Czochralski method. • The crystal has wide absorption and emission bandwidth. • 3.47 W continuous wave laser output with a slope efficiency of 29% was obtained. • The results show that the crystal is a promising ultrashort pulse laser material. - Abstract: A Yb 3+ :Sr 3 Y 2 (BO 3 ) 4 crystal was grown successfully by the Czochralski method. The polarized spectral properties and continuous wave laser output of this crystal were investigated in detail. The crystal has larger absorption and emission cross sections compared with many mature Yb 3+ -doped borate crystals. The full width at half maximum of the emission bands around 1023 nm are 69 nm (E//a), 61 nm (E//b) and 65 nm (E//c). 3.47 W continuous wave laser output with a slope efficiency of 29% and an optical conversion efficiency of 24% was obtained. The results reveal that Yb 3+ :Sr 3 Y 2 (BO 3 ) 4 crystal is an excellent candidate for ultrashort pulse laser crystal

Interaction of ultra-short ultra-intense laser pulses with under-dense plasmas

International Nuclear Information System (INIS)

Solodov, A.

2000-12-01

Different aspects of interaction of ultra-short ultra-intense laser pulses with underdense plasmas are studied analytically and numerically. These studies can be interesting for laser-driven electron acceleration in plasma, X-ray lasers, high-order harmonic generation, initial confinement fusion with fast ignition. For numerical simulations a fully-relativistic particle code WAKE was used, developed earlier at Ecole Polytechnique. It was modified during the work on the thesis in the part of simulation of ion motion, test electron motion, diagnostics for the field and plasma. The studies in the thesis cover the problems of photon acceleration in the plasma wake of a short intense laser pulse, phase velocity of the plasma wave in the Self-Modulated Laser Wake-Field Accelerator (SM LWFA), relativistic channeling of laser pulses with duration of the order of a plasma period, ion dynamics in the wake of a short intense laser pulse, plasma wave breaking. Simulation of three experiments on the laser pulse propagation in plasma and electron acceleration were performed. Among the main results of the thesis, it was found that reduction of the plasma wave phase velocity in the SM LWFA is crucial for electron acceleration, only if a plasma channel is used for the laser pulse guiding. Self-similar structures describing relativistic guiding of short laser pulses in plasmas were found and relativistic channeling of initially Gaussian laser pulses of a few plasma periods in duration was demonstrated. It was shown that ponderomotive force of a plasma wake excited by a short laser pulse forms a channel in plasma and plasma wave breaking in the channel was analyzed in detail. Effectiveness of electron acceleration by the laser field and plasma wave was compared and frequency shift of probe laser pulses by the plasma waves was found in conditions relevant to the current experiments. (author)

Self-Guiding of Ultrashort Relativistically Intense Laser Pulses to the Limit of Nonlinear Pump Depletion

International Nuclear Information System (INIS)

Ralph, J. E.; Marsh, K. A.; Pak, A. E.; Lu, W.; Clayton, C. E.; Fang, F.; Joshi, C.; Tsung, F. S.; Mori, W. B.

2009-01-01

A study of self-guiding of ultra short, relativistically intense laser pulses is presented. Here, the laser pulse length is on the order of the nonlinear plasma wavelength and the normalized vector potential is greater than one. Self-guiding of ultrashort laser pulses over tens of Rayliegh lengths is possible when driving a highly nonlinear wake. In this case, self-guiding is limited by nonlinear pump depletion. Erosion of the pulse due to diffraction at the head of the laser pulse is minimized for spot sizes close to the blow-out radius. This is due to the slowing of the group velocity of the photons at the head of the laser pulse. Using an approximately 10 TW Ti:Sapphire laser with a pulse length of approximately 50 fs, experimental results are presented showing self-guiding over lengths exceeding 30 Rayliegh lengths in various length Helium gas jets. Fully explicit 3D PIC simulations supporting the experimental results are also presented.

Two-dimensional angular energy spectrum of electrons accelerated by the ultra-short relativistic laser pulse

Energy Technology Data Exchange (ETDEWEB)

Borovskiy, A. V. [Department of Computer Science and Cybernetics, Baikal State University of Economics and Law, 11 Lenin Street, Irkutsk 664003 (Russian Federation); Galkin, A. L. [Coherent and Nonlinear Optics Department, A.M. Prokhorov General Physics Institute of the RAS, 38 Vavilov Street, Moscow 119991 (Russian Federation); Department of Physics of MBF, Pirogov Russian National Research Medical University, 1 Ostrovitianov Street, Moscow 117997 (Russian Federation); Kalashnikov, M. P., E-mail: galkin@kapella.gpi.ru [Max-Born-Institute for Nonlinear Optics and Short-Time Spectroscopy, 2a Max-Born-Strasse, Berlin 12489 (Germany)

2015-04-15

The new method of calculating energy spectra of accelerated electrons, based on the parameterization by their initial coordinates, is proposed. The energy spectra of electrons accelerated by Gaussian ultra-short relativistic laser pulse at a selected angle to the axis of the optical system focusing the laser pulse in a low density gas are theoretically calculated. The two-peak structure of the electron energy spectrum is obtained. Discussed are the reasons for its appearance as well as an applicability of other models of the laser field.

X-ray emission as a potential hazard during ultrashort pulse laser material processing

Science.gov (United States)

Legall, Herbert; Schwanke, Christoph; Pentzien, Simone; Dittmar, Günter; Bonse, Jörn; Krüger, Jörg

2018-06-01

In laser machining with ultrashort laser pulses unwanted X-ray radiation in the keV range can be generated when a critical laser intensity is exceeded. Even if the emitted X-ray dose per pulse is low, high laser repetition rates can lead to an accumulation of X-ray doses beyond exposure safety limits. For 925 fs pulse duration at a center wavelength of 1030 nm, the X-ray emission was investigated up to an intensity of 2.6 × 1014 W/cm2. The experiments were performed in air with a thin disk laser at a repetition rate of 400 kHz. X-ray spectra and doses were measured for various planar target materials covering a wide range of the periodic table from aluminum to tungsten. Without radiation shielding, the measured radiation doses at this high repetition rate clearly exceed the regulatory limits. Estimations for an adequate radiation shielding are provided.

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.

Cubic phase control of ultrashort laser pulses

International Nuclear Information System (INIS)

Mecseki, K.; Erdelyi, M.; Kovacs, A.P.; Szabo, G.

2006-01-01

Complete test of publication follows. The temporal shape of an ultrashort laser pulse may change upon propagating through a linear dispersive medium having a phase shift ψω. The change can be characterized by the Taylor-coefficients of the phase shift which are calculated around the central frequency ω 0 of the pulse. Measurements and independent control of the group delay dispersion (GDD, ψ'(ω 0 )) and the third order dispersion (TOD, ψ'(ω 0 )) are important in several research fields, particularly in the generation of ultrashort laser pulses by chirped pulse amplification (CPA) and pulse shaping for molecular control. The GDD and the TOD of an ideal pulse compressor are equal to the negative of the corresponding dispersion coefficients of the medium. However, in the case of prism-pair and grating-pair compressor is different from the ratio of the coefficients of the medium to be compensated for. Therefore it is necessary to develop so-called cubic compressors that are able to control the TOD of the pulse, yet, do not affect the GDD. In this paper a new cubic compressor setup is investigated theoretically and experimentally, which resembles the set-up proposed by White, however, we control the GDD and the TOD by the position of a birefringent, semi-cylinder crystal place around the focal point of an achromatic lens. For the evaluation of the phase shift introduced by the proposed cubic compressor, a ray tracing program was written. The program allows optimizing the compressor parameters, such as the radius of the crystal, magnification of the lens etc. Calcite was applied because it is a strong birefringent material. Calculations showed that there is a trajectory, along which shifting the crystal the TOD can be tuned independently of the GDD. The value of the TOD changed in a relatively wide range between -3.15 x 10 5 fs 3 and -1.67 x 10 5 fs 3 . Although the defocus also affects the angular dispersion of the pulse leaving the compressor, if does not exceed

Ultrashort laser-pulse diagnostics for detection of ordering within an ion beam

International Nuclear Information System (INIS)

Calabrese, R.; Guidi, V.; Lenisa, P.; Mariotti, E.

1996-01-01

A novel diagnostic method to detect ordering within one-dimensional ion beams in a storage ring is presented. The ions are simultaneously excited by a ultrashort pulsed laser (≅1 ps) at two different locations along the beam and fluorescence is detected by a group of four photomultipliers. Correlation in fluorescence signals is a firm indication that the ion beam has an ordered structure. (orig.)

Effect of group velocity mismatch on acousto-optic interaction of ultrashort laser pulses

International Nuclear Information System (INIS)

Yushkov, K B; Molchanov, V Ya

2011-01-01

Equations describing acousto-optic diffraction of ultrashort laser pulses in an anisotropic medium are derived, taking into account the group velocity mismatch of optical eigenmodes. It is shown that the solution of the modified coupled-mode equations taking into account the group delay is characterised by an increase in the pulse duration, a decrease in diffraction efficiency, a change in the shape of the wave packet envelope, as well as by an increase in the width of the transmission function.

Multiphoton photoemission from a copper cathode illuminated by ultrashort laser pulses in an RF photoinjector.

Science.gov (United States)

Musumeci, P; Cultrera, L; Ferrario, M; Filippetto, D; Gatti, G; Gutierrez, M S; Moody, J T; Moore, N; Rosenzweig, J B; Scoby, C M; Travish, G; Vicario, C

2010-02-26

In this Letter we report on the use of ultrashort infrared laser pulses to generate a copious amount of electrons by a copper cathode in an rf photoinjector. The charge yield verifies the generalized Fowler-Dubridge theory for multiphoton photoemission. The emission is verified to be prompt using a two pulse autocorrelation technique. The thermal emittance associated with the excess kinetic energy from the emission process is comparable with the one measured using frequency tripled uv laser pulses. In the high field of the rf gun, up to 50 pC of charge can be extracted from the cathode using a 80 fs long, 2 microJ, 800 nm pulse focused to a 140 mum rms spot size. Taking into account the efficiency of harmonic conversion, illuminating a cathode directly with ir laser pulses can be the most efficient way to employ the available laser power.

Multiphoton Photoemission from a Copper Cathode Illuminated by Ultrashort Laser Pulses in an rf Photoinjector

International Nuclear Information System (INIS)

Musumeci, P.; Gutierrez, M. S.; Moody, J. T.; Moore, N.; Rosenzweig, J. B.; Scoby, C. M.; Travish, G.; Cultrera, L.; Ferrario, M.; Filippetto, D.; Gatti, G.; Vicario, C.

2010-01-01

In this Letter we report on the use of ultrashort infrared laser pulses to generate a copious amount of electrons by a copper cathode in an rf photoinjector. The charge yield verifies the generalized Fowler-Dubridge theory for multiphoton photoemission. The emission is verified to be prompt using a two pulse autocorrelation technique. The thermal emittance associated with the excess kinetic energy from the emission process is comparable with the one measured using frequency tripled uv laser pulses. In the high field of the rf gun, up to 50 pC of charge can be extracted from the cathode using a 80 fs long, 2 μJ, 800 nm pulse focused to a 140 μm rms spot size. Taking into account the efficiency of harmonic conversion, illuminating a cathode directly with ir laser pulses can be the most efficient way to employ the available laser power.

Bright ultrashort x-rays from intense subpicosecond laser-plasma interactions

International Nuclear Information System (INIS)

Umstadter, D.

1995-01-01

Short-pulse, high-intensity lasers interacting with solid targets make possible the study of a new class of laser-plasma interactions. They are unique because during the ultrashort laser pulse relatively little expansion occurs, and the density scale length remains much less than the laser wavelength. This makes possible the direct deposition of a significant amount of the laser energy at close to solid density. Steep plasma temperature and density gradients subsequently cause rapid cooling, resulting in highly non-equilibrium conditions and the concurrent emission of extremely bright ultrashort x-ray pulses. In this study, the latter are investigated experimentally with temporally and spectrally resolved soft x-ray diagnostics. The emitted x-ray spectra from solid targets with various atomic numbers are characterized for a laser pulse width τ l ∼ 400 fs. These ultrashort x rays may be used as (1) a diagnostic of solid-density plasma conditions, (2) a tool for the study of radiation hydrodynamics in a parameter regime that is otherwise inaccessible, and (3) a source for time-resolved diffraction, spectroscopy, or microscopy studies of transient chemical, biological or physical phenomena

Optical third-harmonic generation using ultrashort laser pulses

International Nuclear Information System (INIS)

Stoker, D.; Keto, J.W.; Becker, M.F.

2005-01-01

To better predict optical third-harmonic generation (THG) in transparent dielectrics, we model a typical ultrashort pulsed Gaussian beam, including both group velocity mismatch and phase mismatch of the fundamental and harmonic fields. We find that competition between the group velocity mismatch and phase mismatch leads to third-harmonic generation that is sensitive only to interfaces. In this case, the spatial resolution is determined by the group velocity walk-off length. THG of modern femtosecond lasers in optical solids is a bulk process, without a surface susceptibility, but bears the signature of a surface enhancement effect in z-scan measurements. We demonstrate the accuracy of the model, by showing the agreement between the predicted spectral intensity and the measured third-harmonic spectrum from a thin sapphire crystal

Optimization And Single-Shot Characterization Of Ultrashort Thz Pulses From A Laser Wakefield Accelerator

International Nuclear Information System (INIS)

Plateau, G.R.; Matlis, N.H.; van Tilborg, J.; Geddes, C.G.R.; Toth, Cs.; Schroeder, C.B.; Leemans, W.P.

2009-01-01

We present spatiotemporal characterization of μJ-class ultrashort THz pulses generated from a laser wakefield accelerator (LWFA). Accelerated electrons, resulting from the interaction of a high-intensity laser pulse with a plasma, emit high-intensity THz pulses as coherent transition radiation. Such high peak-power THz pulses, suitable for high-field (MV/cm) pump-probe experiments, also provide a non-invasive bunch-length diagnostic and thus feedback for the accelerator. The characterization of the THz pulses includes energy measurement using a Golay cell, 2D sign-resolved electro-optic measurement and single-shot spatiotemporal electric-field distribution retrieval using a new technique, coined temporal electric-field cross-Correlation (TEX). All three techniques corroborate THz pulses of ∼ 5 μJ, with peak fields of 100's of kV/cm and ∼ 0.4 ps rms duration.

A high-order corrected description of ultra-short and tightly focused laser pulses, and their electron acceleration in vacuum

International Nuclear Information System (INIS)

Zhang, J.T.; Wang, P.X.; Kong, Q.; Chen, Z.; Ho, Y.K.

2007-01-01

Field expressions are derived for ultra-short, tightly focused laser pulses up to the second-order temporal correction and seventh-order spatial correction. To evaluate the importance of these corrections, we simulate these fields and investigate the final energy of the accelerated electrons. We vary the order of the corrected expressions, the pulse duration, and the beam waist. We find that electron capture is still an important and generic phenomenon in ultra-short, tightly focused laser pulses. While small differences in the electron acceleration are obtained for various orders of the corrected field equations relative to the paraxial field equations, there is no qualitative difference in the behavior of the electron. Furthermore, the temporal and spatial corrections are found to be correlated

Triggering and guiding high-voltage large-scale leader discharges with sub-joule ultrashort laser pulses

International Nuclear Information System (INIS)

Pepin, H.; Comtois, D.; Vidal, F.; Chien, C.Y.; Desparois, A.; Johnston, T.W.; Kieffer, J.C.; La Fontaine, B.; Martin, F.; Rizk, F.A.M.; Potvin, C.; Couture, P.; Mercure, H.P.; Bondiou-Clergerie, A.; Lalande, P.; Gallimberti, I.

2001-01-01

The triggering and guiding of leader discharges using a plasma channel created by a sub-joule ultrashort laser pulse have been studied in a megavolt large-scale electrode configuration (3-7 m rod-plane air gap). By focusing the laser close to the positive rod electrode it has been possible, with a 400 mJ pulse, to trigger and guide leaders over distances of 3 m, to lower the leader inception voltage by 50%, and to increase the leader velocity by a factor of 10. The dynamics of the breakdown discharges with and without the laser pulse have been analyzed by means of a streak camera and of electric field and current probes. Numerical simulations have successfully reproduced many of the experimental results obtained with and without the presence of the laser plasma channel

The interaction of super-intense ultra-short laser pulse and micro-clusters with large atomic clusters

International Nuclear Information System (INIS)

Miao Jingwei; Yang Chaowen; An Zhu; Yuan Xuedong; Sun Weiguo; Luo Xiaobing; Wang Hu; Bai Lixing; Shi Miangong; Miao Lei; Zhen Zhijian; Gu Yuqin; Liu Hongjie; Zhu Zhouseng; Sun Liwei; Liao Xuehua

2007-01-01

The fusion mechanism of large deuterium clusters (100-1000 Atoms/per cluster) in super-intense ultra-short laser pulse field, Coulomb explosions of micro-cluster in solids, gases and Large-size clusters have been studied using the interaction of a high-intensity femtosecond laser pulses with large deuterium clusters, collision of high-quality beam of micro-cluster from 2.5 MV van de Graaff accelerator with solids, gases and large clusters. The experimental advance of the project is reported. (authors)

Optical reprogramming of human somatic cells using ultrashort Bessel-shaped near-infrared femtosecond laser pulses

Science.gov (United States)

Uchugonova, Aisada; Breunig, Hans Georg; Batista, Ana; König, Karsten

2015-11-01

We report a virus-free optical approach to human cell reprogramming into induced pluripotent stem cells with low-power nanoporation using ultrashort Bessel-shaped laser pulses. Picojoule near-infrared sub-20 fs laser pulses at a high 85 MHz repetition frequency are employed to generate transient nanopores in the membrane of dermal fibroblasts for the introduction of four transcription factors to induce the reprogramming process. In contrast to conventional approaches which utilize retro- or lentiviruses to deliver genes or transcription factors into the host genome, the laser method is virus-free; hence, the risk of virus-induced cancer generation limiting clinical application is avoided.

Water spray assisted ultrashort laser pulse ablation

International Nuclear Information System (INIS)

Silvennoinen, M.; Kaakkunen, J.J.J.; Paivasaari, K.; Vahimaa, P.

2013-01-01

Highlights: ► We show the novel method to use multibeam processing with ultrashort pulses efficiently. ► Sprayed thin water layer on ablation zone enhances ablation rate and quality. ► In some cases this method also enables ablation of the deeper and straighter holes compared to ones made without the water layer. ► Method also makes possible to directly write features without the self-organizing structures. - Abstract: We have studied femtosecond ablation under sprayed thin water film and its influence and benefits compared with ablation in the air atmosphere. These have been studied in case of the hole and the groove ablation using IR femtosecond laser. Water enhances the ablation rate and in some situations it makes possible to ablate the holes with a higher aspect ratio. While ablating the grooves, the water spray allows using the high fluences without the generation of the self-organized structures.

Ultrashort Generation Regimes in the All-Fiber Kerr Mode-Locked Erbium-Doped Fiber Ring Laser for Terahertz Pulsed Spectroscopy

Directory of Open Access Journals (Sweden)

V. S. Voropaev

2015-01-01

Full Text Available Many femtosecond engineering applications require for a stable generation of ultrashort pulses. Thus, in the terahertz pulsed spectroscopy a measurement error in the refractive index is strongly dependent on the pulse duration stability with allowable variation of few femtoseconds. The aim of this work is to study the ultrashort pulses (USP regimes stability in the all – fiber erbium doped ring laser with Kerr mode-locking. The study was conducted at several different values of the total resonator intra-cavity dispersion. Three laser schemes with the intra-cavity dispersion values from -1.232 ps2 to +0.008 ps2 have been studied. In the experiment there were two regimes of generation observed: the stretched pulse generation and ordinary soliton generation. Main attention is focused on the stability of regimes under study. The most stable regime was that of the stretched pulse generation with a spectrum form of sech2 , possible pulse duration of 490 fs at least, repetition rate of 2.9 MHz, and average output power of 17 mW. It is worth noting, that obtained regimes had characteristics suitable for the successful use in the terahertz pulsed spectroscopy. The results may be useful in the following areas of science and technology: a high-precision spectroscopy, optical frequency standards, super-continuum generation, and terahertz pulsed spectroscopy. The future system development is expected to stabilize duration and repetition rate of the obtained regime of ultra-short pulse generation.

Proceedings of the first JAERI-Kansai international workshop on ultrashort-pulse ultrahigh-power lasers and simulation for laser-plasma interactions

International Nuclear Information System (INIS)

1998-03-01

Records of the First JAERI-Kansai International Workshop, which focused on the subject of 'Ultrashort-Pulse Ultrahigh-Power Lasers and Simulation for Laser-Plasma Interactions', are contained in this issue. The First JAERI-Kansai International Workshop was held as Joint ICFA/JAERI-Kansai International Workshop '97 with International Committee for Future Accelerators (ICFA). This report consists of 24 contributed papers. (J.P.N.)

Proceedings of the first JAERI-Kansai international workshop on ultrashort-pulse ultrahigh-power lasers and simulation for laser-plasma interactions

Energy Technology Data Exchange (ETDEWEB)

NONE

1998-03-01

Records of the First JAERI-Kansai International Workshop, which focused on the subject of `Ultrashort-Pulse Ultrahigh-Power Lasers and Simulation for Laser-Plasma Interactions`, are contained in this issue. The First JAERI-Kansai International Workshop was held as Joint ICFA/JAERI-Kansai International Workshop `97 with International Committee for Future Accelerators (ICFA). This report consists of 24 contributed papers. (J.P.N.)

How to optimize ultrashort pulse laser interaction with glass surfaces in cutting regimes?

Energy Technology Data Exchange (ETDEWEB)

Bulgakova, Nadezhda M., E-mail: bulgakova@fzu.cz [HiLASE Centre, Institute of Physics ASCR, Za Radnicí 828, 25241 Dolní Břežany (Czech Republic); Institute of Thermophysics SB RAS, 1 Lavrentyev Ave., Novosibirsk 630090 (Russian Federation); Zhukov, Vladimir P. [Institute of Computational Technologies SB RAS, 6 Lavrentyev Ave., 630090 Novosibirsk (Russian Federation); Novosibirsk State Technical University, 20 Karl Marx Ave., 630073 Novosibirsk (Russian Federation); Collins, Adam R. [NCLA, NUI Galway, Galway (Ireland); Rostohar, Danijela; Derrien, Thibault J.-Y.; Mocek, Tomáš [HiLASE Centre, Institute of Physics ASCR, Za Radnicí 828, 25241 Dolní Břežany (Czech Republic)

2015-05-01

Highlights: • The factors influencing laser micromachining of transparent materials are analyzed. • Important role of ambient gas in laser processing is shown by numerical simulations. • The large potential of bi-wavelength laser processing is demonstrated. - Abstract: The interaction of short and ultrashort pulse laser radiation with glass materials is addressed. Particular attention is paid to regimes which are important in industrial applications such as laser cutting, drilling, functionalization of material surfaces, etc. Different factors influencing the ablation efficiency and quality are summarized and their importance is illustrated experimentally. The effects of ambient gas ionization in front of the irradiated target are also analyzed. A possibility to enhance laser coupling with transparent solids by bi-wavelength irradiation is discussed.

Modelling of the energy density deposition profiles of ultrashort laser pulses focused in optical media

International Nuclear Information System (INIS)

Vidal, F; Lavertu, P-L; Bigaouette, N; Moore, F; Brunette, I; Giguere, D; Kieffer, J-C; Olivie, G; Ozaki, T

2007-01-01

The propagation of ultrashort laser pulses in dense optical media is investigated theoretically by solving numerically the nonlinear Schroedinger equation. It is shown that the maximum energy density deposition as a function of the pulse energy presents a well-defined threshold that increases with the pulse duration. As a consequence of plasma defocusing, the maximum energy density deposition is generally smaller and the size of the energy deposition zone is generally larger for shorter pulses. Nevertheless, significant values of the energy density deposition can be obtained near threshold, i.e., at lower energy than for longer pulses

Surface Texturing of CVD Diamond Assisted by Ultrashort Laser Pulses

Directory of Open Access Journals (Sweden)

Daniele M. Trucchi

2017-11-01

Full Text Available Diamond is a wide bandgap semiconductor with excellent physical properties which allow it to operate under extreme conditions. However, the technological use of diamond was mostly conceived for the fabrication of ultraviolet, ionizing radiation and nuclear detectors, of electron emitters, and of power electronic devices. The use of nanosecond pulse excimer lasers enabled the microstructuring of diamond surfaces, and refined techniques such as controlled ablation through graphitization and etching by two-photon surface excitation are being exploited for the nanostructuring of diamond. On the other hand, ultrashort pulse lasers paved the way for a more accurate diamond microstructuring, due to reduced thermal effects, as well as an effective surface nanostructuring, based on the formation of periodic structures at the nanoscale. It resulted in drastic modifications of the optical and electronic properties of diamond, of which “black diamond” films are an example for future high-temperature solar cells as well as for advanced optoelectronic platforms. Although experiments on diamond nanostructuring started almost 20 years ago, real applications are only today under implementation.

Prospects for a novel ultrashort pulsed laser technology for pathogen inactivation

Directory of Open Access Journals (Sweden)

Tsen Shaw-Wei D

2012-07-01

Full Text Available Abstract The threat of emerging pathogens and microbial drug resistance has spurred tremendous efforts to develop new and more effective antimicrobial strategies. Recently, a novel ultrashort pulsed (USP laser technology has been developed that enables efficient and chemical-free inactivation of a wide spectrum of viral and bacterial pathogens. Such a technology circumvents the need to introduce potentially toxic chemicals and could permit safe and environmentally friendly pathogen reduction, with a multitude of possible applications including the sterilization of pharmaceuticals and blood products, and the generation of attenuated or inactivated vaccines.

Generation of ultra-short relativistic-electron-bunch by a laser wakefield

NARCIS (Netherlands)

Khachatryan, A.G.; Boller, Klaus J.; van Goor, F.A.

2003-01-01

The possibility of the generation of an ultra-short (about one micron long) relativistic (up to a few GeVs) electron-bunch in a moderately nonlinear laser wakefield excited in an underdense plasma by an intense laser pulse is investigated. The ultra-short bunch is formed by trapping, effective

Texturing in titanium grade 2 surface irradiate with ultrashort pulse laser

International Nuclear Information System (INIS)

Nogueira, Alessandro Francelino

2015-01-01

The texturing laser micromachining is an important alternative to improve the bonding adhesion between composites and titanium, which are applied to structural components in the aerospace industry. The texturing running on titanium plates is due to the fact that the preferred joining technique for many composite materials is the adhesive bonding. In this work, titanium plates were texturized using laser ultrashort pulses temporal widths of femtoseconds. This process resulted in minimal heat transfer to the material, avoiding deformation of the titanium plate surface as well as the formation of resolidified material in the ablated region. These drawbacks have occurred with the use of nanoseconds pulses. Were performed three types of texturing using laser with femtosecond pulses, with variations in the distances between the machined lines. The analysis of the obtained surfaces found that the wettability increases when there is the increased distance between the texturing lines. Advancing in the analysis by optical profilometry of textured surfaces was observed that there is substantial increase in the volume available for penetration of structural adhesive when the distances between the textured lines are diminished. In tensile tests conducted it was observed that there is an increase in shear strength of the adhesive joint by reducing the distance between the textured lines. (author)

Investigation of ultrashort-pulsed laser on dental hard tissue

Science.gov (United States)

Uchizono, Takeyuki; Awazu, Kunio; Igarashi, Akihiro; Kato, Junji; Hirai, Yoshito

2007-02-01

Ultrashort-pulsed laser (USPL) can ablate various materials with precious less thermal effect. In laser dentistry, to solve the problem that were the generation of crack and carbonized layer by irradiating with conventional laser such as Er:YAG and CO II laser, USPL has been studied to ablate dental hard tissues by several researchers. We investigated the effectiveness of ablation on dental hard tissues by USPL. In this study, Ti:sapphire laser as USPL was used. The laser parameter had the pulse duration of 130 fsec, 800nm wavelength, 1KHz of repetition rate and the average power density of 90~360W/cm2. Bovine root dentin plates and crown enamel plates were irradiated with USPL at 1mm/sec using moving stage. The irradiated samples were analyzed by SEM, EDX, FTIR and roughness meter. In all irradiated samples, the cavity margin and wall were sharp and steep, extremely. In irradiated dentin samples, the surface showed the opened dentin tubules and no smear layer. The Ca/P ratio by EDX measurement and the optical spectrum by FTIR measurement had no change on comparison irradiated samples and non-irradiated samples. These results confirmed that USPL could ablate dental hard tissue, precisely and non-thermally. In addition, the ablation depths of samples were 10μm, 20μm, and 60μm at 90 W/cm2, 180 W/cm2, and 360 W/cm2, approximately. Therefore, ablation depth by USPL depends on the average power density. USPL has the possibility that can control the precision and non-thermal ablation with depth direction by adjusting the irradiated average power density.

High-throughput machining using high average power ultrashort pulse lasers and ultrafast polygon scanner

Science.gov (United States)

Schille, Joerg; Schneider, Lutz; Streek, André; Kloetzer, Sascha; Loeschner, Udo

2016-03-01

In this paper, high-throughput ultrashort pulse laser machining is investigated on various industrial grade metals (Aluminium, Copper, Stainless steel) and Al2O3 ceramic at unprecedented processing speeds. This is achieved by using a high pulse repetition frequency picosecond laser with maximum average output power of 270 W in conjunction with a unique, in-house developed two-axis polygon scanner. Initially, different concepts of polygon scanners are engineered and tested to find out the optimal architecture for ultrafast and precision laser beam scanning. Remarkable 1,000 m/s scan speed is achieved on the substrate, and thanks to the resulting low pulse overlap, thermal accumulation and plasma absorption effects are avoided at up to 20 MHz pulse repetition frequencies. In order to identify optimum processing conditions for efficient high-average power laser machining, the depths of cavities produced under varied parameter settings are analyzed and, from the results obtained, the characteristic removal values are specified. The maximum removal rate is achieved as high as 27.8 mm3/min for Aluminium, 21.4 mm3/min for Copper, 15.3 mm3/min for Stainless steel and 129.1 mm3/min for Al2O3 when full available laser power is irradiated at optimum pulse repetition frequency.

Photoionization of atoms and molecules by intense EUV-FEL pulses and FEL seeded by high-order harmonic of ultrashort laser pulses

International Nuclear Information System (INIS)

Iwasaki, Atsushi; Owada, Shigeki; Yamanouchi, Kaoru; Sato, Takahiro; Nagasono, Mitsuru; Yabashi, Makina; Ishikawa, Tetsuya; Togashi, Tadashi; Takahashi, Eiji J.; Midorikawa, Katsumi; Aoyama, Makoto; Yamakawa, Koichi; Kannari, Fumihiko; Yagishita, Akira

2012-01-01

The advantages of SPring-8 Compact SASE Source as a light source for spectroscopic measurements in the extreme ultraviolet (EUV) wavelength region are introduced by referring to our recent study of non-linear photoionization processes of He, in which the absolute two-photon ionization cross sections of He at four different wavelengths in the 54 - 62 nm region were determined using intense pulses of the free-election laser (FEL). In addition, our recent effort to generate intense full-coherent EUV light pulses are introduced, in which significant amplification of the 13th harmonic of ultrashort laser pulses at 800 nm was achieved by FEL seeded with the 13th harmonic. (author)

Study of 2ω and 3/2ω harmonics in ultrashort high-intensity laser ...

Indian Academy of Sciences (India)

Intense laser pulses from such laser systems may have many pre-pulses like picosecond ... ultrashort laser–matter interaction, as well as to control the source parameters. In situ monitoring of ultrashort ... central wavelength of 790 nm with a bandwidth of 16 ± 2 nm after the compressor. The picosecond intensity contrast ...

Atomistic simulations of ultra-short pulse laser ablation of aluminum: validity of the Lambert-Beer law

Science.gov (United States)

Eisfeld, Eugen; Roth, Johannes

2018-05-01

Based on hybrid molecular dynamics/two-temperature simulations, we study the validity of the application of Lambert-Beer's law, which is conveniently used in various modeling approaches of ultra-short pulse laser ablation of metals. The method is compared to a more rigorous treatment, which involves solving the Helmholtz wave equation for different pulse durations ranging from 100 fs to 5 ps and a wavelength of 800 nm. Our simulations show a growing agreement with increasing pulse durations, and we provide appropriate optical parameters for all investigated pulse durations.

Interaction of Rydberg atoms with two contrapropagating ultrashort laser pulses

International Nuclear Information System (INIS)

Lugovskoy, A. V.; Bray, I.

2006-01-01

In this paper we investigate how Rydberg atoms respond to perturbation by two contrapropagating ultrashort laser pulses. We consider the case where the durations of both pulses τ 1 and τ 2 are shorter than the inverse of the initial-state energy ε i -1 . When acting alone such a pulse passes through the atom without noticeable alteration in the atomic state. The situation is different if two such pulses interfere in the region of atom localization. In this case the atomic response is significantly enhanced. This is due to the nonzero momentum transferred to the electron by the interplay of the electric field of one pulse and the magnetic field of the other. The sudden perturbation approximation is used to evaluate the transition probabilities. They are shown to depend on the atom position with respect to the pulse interference region. This dependence is determined by the relationship between the atomic diameter d i and the interference-region size l=c(τ 1 +τ 2 ) (c is the speed of light). If d i i >>l the transition probabilities are sensitive to the electron density distribution along the propagation direction. The probabilities of the initial-state destruction and atom ionization drop as l/d i irrespective of the characteristics of the pulses

High power ultrashort pulse lasers

International Nuclear Information System (INIS)

Perry, M.D.

1994-01-01

Small scale terawatt and soon even petawatt (1000 terawatt) class laser systems are made possible by application of the chirped-pulse amplification technique to solid-state lasers combined with the availability of broad bandwidth materials. These lasers make possible a new class of high gradient accelerators based on the large electric fields associated with intense laser-plasma interactions or from the intense laser field directly. Here, we concentrate on the laser technology to produce these intense pulses. Application of the smallest of these systems to the production of high brightness electron sources is also introduced

Interaction of ultrashort pulses with molecules and solids: Physics ...

Indian Academy of Sciences (India)

2014-07-26

energy materials. Abstract. The interaction of ultrashort laser pulses with molecules and solids is an extremely complex area of science research encompassing the fields of physics, chemistry, and materials science. The physics ...

Interaction of intense ultrashort pulse lasers with clusters

International Nuclear Information System (INIS)

Petrov, G. M.; Davis, J.

2008-01-01

The dynamics of clusters composed of different material irradiated by a high-intensity ultrashort pulse laser was studied using a fully relativistic three-dimensional molecular dynamics model. Key parameters of the cluster evolution such as particle positions, energy absorption, and cluster explosion were simulated. By a direct comparison of these parameters for clusters of equal initial radius but made of different material (deuterium, neon, argon, and xenon), the main stages and attributes of cluster evolution were elucidated. The simulations showed that clusters made of different material act alike, especially those of heavy elements. Clusters made of heavy elements (neon, argon, and xenon) differentiate from clusters made of light elements (deuterium) by the magnitude of the absorbed energy per cluster and the final mean energy of exploding ions. What most distinguishes clusters composed of different material is the amount of emitted radiation and its spectral range

Fast Prototyping of Sensorized Cell Culture Chips and Microfluidic Systems with Ultrashort Laser Pulses

Directory of Open Access Journals (Sweden)

Sebastian M. Bonk

2015-03-01

Full Text Available We developed a confined microfluidic cell culture system with a bottom plate made of a microscopic slide with planar platinum sensors for the measurement of acidification, oxygen consumption, and cell adhesion. The slides were commercial slides with indium tin oxide (ITO plating or were prepared from platinum sputtering (100 nm onto a 10-nm titanium adhesion layer. Direct processing of the sensor structures (approximately three minutes per chip by an ultrashort pulse laser facilitated the production of the prototypes. pH-sensitive areas were produced by the sputtering of 60-nm Si3N4 through a simple mask made from a circuit board material. The system body and polydimethylsiloxane (PDMS molding forms for the microfluidic structures were manufactured by micromilling using a printed circuit board (PCB milling machine for circuit boards. The microfluidic structure was finally imprinted in PDMS. Our approach avoided the use of photolithographic techniques and enabled fast and cost-efficient prototyping of the systems. Alternatively, the direct production of metallic, ceramic or polymeric molding tools was tested. The use of ultrashort pulse lasers improved the precision of the structures and avoided any contact of the final structures with toxic chemicals and possible adverse effects for the cell culture in lab-on-a-chip systems.

Ultrashort hard x-ray pulses generated by 90 degrees Thomson scattering

International Nuclear Information System (INIS)

Chin, A.H.; Schoenlein, R.W.; Glover, T.E.

1997-01-01

Ultrashort x-ray pulses permit observation of fast structural dynamics in a variety of condensed matter systems. The authors have generated 300 femtosecond, 30 keV x-ray pulses by 90 degrees Thomson scattering between femtosecond laser pulses and relativistic electrons. The x-ray and laser pulses are synchronized on a femtosecond time scale, an important prerequisite for ultrafast pump-probe spectroscopy. Analysis of the x-ray beam properties also allows for electron bunch characterization on a femtosecond time scale

Analytical performances of laser-induced micro-plasma of Al samples with single and double ultrashort pulses in air and with Ar-jet: A comparative study

International Nuclear Information System (INIS)

Semerok, A.; Dutouquet, C.

2014-01-01

Ultrashort pulse laser microablation coupled with optical emission spectroscopy was under study to obtain several micro-LIBS analytical features (shot-to-shot reproducibility, spectral line intensity and lifetime, calibration curves, detection limits). Laser microablation of Al matrix samples with known Cu- and Mg-concentrations was performed by single and double pulses of 50 fs and 1 ps pulse duration in air and with Ar-jet. The micro-LIBS analytical features obtained under different experimental conditions were characterized and compared. The highest shot-to-shot reproducibility and gain in plasma spectral line intensity were obtained with double pulses with Ar-jet for both 50 fs and 1 ps pulse durations. The best calibration curves were obtained with 1 ps pulse duration with Ar-jet. Micro-LIBS with ultrashort double pulses may find its effective application for surface elemental microcartography. - Highlights: • Analytical performances of micro-LIBS with ultrashort double pulses were studied. • The maximal line intensity gain of 20 was obtained with double pulses and Ar-jet. • LIBS gain was obtained without additional ablation of a sample by the second pulse. • LIBS properties were almost the same for both 50 fs and 1 ps pulses. • The micro-LIBS detection limit was around 35 ppm

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.

Ultra-short laser processing of transparent material at the interface to liquid

International Nuclear Information System (INIS)

Boehme, R; Pissadakis, S; Ehrhardt, M; Ruthe, D; Zimmer, K

2006-01-01

Similarly to laser-induced backside wet etching (LIBWE) with nanosecond ultraviolet (ns UV) laser pulses, the irradiation of the solid/liquid interface of fused silica with sub-picosecond (sub-ps) UV and femtosecond near infrared (fs NIR) laser pulses results in etching of the fused silica surface and deposition of decomposition products from liquid. Furthermore, the etch threshold is reduced compared with both direct ablation with an fs laser in air and backside etching with UV ns pulses. Using 0.5 M pyrene/toluene as absorbing liquid, the thresholds were determined to be 70 mJ cm -2 (sub-ps UV) and 330 mJ cm -2 (fs NIR). Furthermore, an almost linear increase in the etch rate with increasing laser fluence was found. The roughness of surfaces backside etched with ultra-short pulses is higher in comparison with ns pulses but lower than that obtained using direct fs laser ablation. Hence a combination of processes involved in fs laser ablation and ns backside etching can be expected. The processes at the ultra-short pulse laser irradiated solid/liquid interface are discussed, considering the effects of ultra-fast heating, multi-photon absorption processes, as well as defect generation in the materials

ANALYSIS OF PERIODIC NANOSTRUCTURES FORMATION ON A GOLD SURFACE UNDER EXPOSURE TO ULTRASHORT LASER PULSES NEAR THE MELTING THRESHOLD

Directory of Open Access Journals (Sweden)

D. S. Ivanov

2015-11-01

Full Text Available Subject of Study. The mechanism of surface restructuring by ultrashort laser pulses involves a lot of fast, non-equilibrium, and interrelated processes while the solid is in a transient state. As a result, the analysis of the experimental data cannot cover all the mechanisms of nanostructuring. We present a direct comparison of a simulation and experimental results of surface nanomodification induced by a single laser pulse. Method. The experimental results were obtained by using a mask projection setup with a laser wavelength equal to 248 nm and a pulse length equal to 1.6 ps. This setup is used to produce an intensity grating on a gold surface with a sinusoidal shape and a period of 500 nm. The formed structures were analyzed by a scanning and transmission electron microscope, respectively. Then a hybrid atomistic-continuum model capable of capturing the essential mechanisms responsible for the nanostructuring process was used for modeling the interaction of the laser pulse with a thick gold target. Main Results. A good agreement between simulation and experimental data justifies the proposed approach as a powerful tool revealing the physics behind the nanostructuring process at a gold surface and providing a microscopic insight into the dynamics of the structuring processes of metals in general. The presented model, therefore, is an important step towards a new computational tool in predicting materials response to an ultrashort laser pulse on the atomic scale and properties of the modified surfaces. Practical Relevance. This detailed understanding of the dynamics of the process will pave the way towards pre-designed topologies for functionalized surfaces on the nano- and micro-scales.

Ultra-short pulse delivery at high average power with low-loss hollow core fibers coupled to TRUMPF's TruMicro laser platforms for industrial applications

Science.gov (United States)

Baumbach, S.; Pricking, S.; Overbuschmann, J.; Nutsch, S.; Kleinbauer, J.; Gebs, R.; Tan, C.; Scelle, R.; Kahmann, M.; Budnicki, A.; Sutter, D. H.; Killi, A.

2017-02-01

Multi-megawatt ultrafast laser systems at micrometer wavelength are commonly used for material processing applications, including ablation, cutting and drilling of various materials or cleaving of display glass with excellent quality. There is a need for flexible and efficient beam guidance, avoiding free space propagation of light between the laser head and the processing unit. Solid core step index fibers are only feasible for delivering laser pulses with peak powers in the kW-regime due to the optical damage threshold in bulk silica. In contrast, hollow core fibers are capable of guiding ultra-short laser pulses with orders of magnitude higher peak powers. This is possible since a micro-structured cladding confines the light within the hollow core and therefore minimizes the spatial overlap between silica and the electro-magnetic field. We report on recent results of single-mode ultra-short pulse delivery over several meters in a lowloss hollow core fiber packaged with industrial connectors. TRUMPF's ultrafast TruMicro laser platforms equipped with advanced temperature control and precisely engineered opto-mechanical components provide excellent position and pointing stability. They are thus perfectly suited for passive coupling of ultra-short laser pulses into hollow core fibers. Neither active beam launching components nor beam trackers are necessary for a reliable beam delivery in a space and cost saving packaging. Long term tests with weeks of stable operation, excellent beam quality and an overall transmission efficiency of above 85 percent even at high average power confirm the reliability for industrial applications.

Mimicking lizard-like surface structures upon ultrashort laser pulse irradiation of inorganic materials

Science.gov (United States)

Hermens, U.; Kirner, S. V.; Emonts, C.; Comanns, P.; Skoulas, E.; Mimidis, A.; Mescheder, H.; Winands, K.; Krüger, J.; Stratakis, E.; Bonse, J.

2017-10-01

Inorganic materials, such as steel, were functionalized by ultrashort laser pulse irradiation (fs- to ps-range) to modify the surface's wetting behavior. The laser processing was performed by scanning the laser beam across the surface of initially polished flat sample material. A systematic experimental study of the laser processing parameters (peak fluence, scan velocity, line overlap) allowed the identification of different regimes associated with characteristic surface morphologies (laser-induced periodic surface structures, grooves, spikes, etc.). Analyses of the surface using optical as well as scanning electron microscopy revealed morphologies providing the optimum similarity to the natural skin of lizards. For mimicking skin structures of moisture-harvesting lizards towards an optimization of the surface wetting behavior, additionally a two-step laser processing strategy was established for realizing hierarchical microstructures. In this approach, micrometer-scaled capillaries (step 1) were superimposed by a laser-generated regular array of small dimples (step 2). Optical focus variation imaging measurements finally disclosed the three dimensional topography of the laser processed surfaces derived from lizard skin structures. The functionality of these surfaces was analyzed in view of wetting properties.

Guiding of laser pulses in plasma waveguides created by linearly-polarized femtosecond laser pulses

OpenAIRE

Lemos, N.; Cardoso, L.; Geada, J.; Figueira, G.; Albert, F.; Dias, J. M.

2018-01-01

We experimentally demonstrate that plasma waveguides produced with ultra-short laser pulses (sub-picosecond) in gas jets are capable of guiding high intensity laser pulses. This scheme has the unique ability of guiding a high-intensity laser pulse in a plasma waveguide created by the same laser system in the very simple and stable experimental setup. A hot plasma column was created by a femtosecond class laser that expands into an on-axis parabolic low density profile suitable to act as a wav...

Graphics-processing-unit-accelerated finite-difference time-domain simulation of the interaction between ultrashort laser pulses and metal nanoparticles

Science.gov (United States)

Nikolskiy, V. P.; Stegailov, V. V.

2018-01-01

Metal nanoparticles (NPs) serve as important tools for many modern technologies. However, the proper microscopic models of the interaction between ultrashort laser pulses and metal NPs are currently not very well developed in many cases. One part of the problem is the description of the warm dense matter that is formed in NPs after intense irradiation. Another part of the problem is the description of the electromagnetic waves around NPs. Description of wave propagation requires the solution of Maxwell’s equations and the finite-difference time-domain (FDTD) method is the classic approach for solving them. There are many commercial and free implementations of FDTD, including the open source software that supports graphics processing unit (GPU) acceleration. In this report we present the results on the FDTD calculations for different cases of the interaction between ultrashort laser pulses and metal nanoparticles. Following our previous results, we analyze the efficiency of the GPU acceleration of the FDTD algorithm.

Excitation of hydrogen atom by ultrashort laser pulses in optically dense plasma

Energy Technology Data Exchange (ETDEWEB)

Calisti, A. [Aix Marseille Universite, CNRS, PIIM, Marseille (France); Astapenko, V.A. [Moscow Institute of Physics and Technology, Dolgoprudnyi (Russian Federation); Lisitsa, V.S. [Moscow Institute of Physics and Technology, Dolgoprudnyi (Russian Federation); Russian Research Center ' ' Kurchatov Institute' ' , Moscow (Russian Federation); National Research Nuclear University MEPhI, Moscow (Russian Federation)

2017-10-15

The features of excitation of a hydrogen atom by ultrashort laser pulses (USP) with a Gaussian envelope in optically dense plasma at a Lyman-beta transition are studied theoretically. The problem is of interest for diagnostics of optically dense media. USP have two doubtless advantages over conventional laser excitation: (a) the USP carrier frequency is shifted to the region of short wavelengths allowing exciting atoms from the ground state and (b) the wide spectrum of USP allows them to penetrate into optically dense media to much longer distances as compared with monochromatic radiation. As actual realistic cases, two examples are considered: hot rarefied plasma (the coronal limit) and dense cold plasma (the Boltzmann equilibrium). Universal expressions for the total probability of excitation of the transition under consideration are obtained in view of absorption of radiation in a medium. As initial data for the spectral form of a line, the results of calculations by methods of molecular dynamics are used. The probability of excitation of an atom is analysed for different values of problem parameters: the pulse duration, the optical thickness of a medium, and the detuning of the pulse carrier frequency from the eigenfrequency of an electron transition. (copyright 2017 WILEY-VCH Verlag GmbH and Co. KGaA, Weinheim)

Time-dependent H-like and He-like Al lines produced by ultra-short pulse laser

Energy Technology Data Exchange (ETDEWEB)

Kato, Takako; Kato, Masatoshi [National Inst. for Fusion Science, Nagoya (Japan); Shepherd, R; Young, B; More, R; Osterheld, Al

1998-03-01

We have performed numerical modeling of time-resolved x-ray spectra from thin foil targets heated by the LLNL Ultra-short pulse (USP) laser. The targets were aluminum foils of thickness ranging from 250 A to 1250 A, heated with 120 fsec pulses of 400 nm light from the USP laser. The laser energy was approximately 0.2 Joules, focused to a 3 micron spot size for a peak intensity near 2 x 10{sup 19} W/cm{sup 2}. Ly{alpha} and He{alpha} lines were recorded using a 900 fsec x-ray streak camera. We calculate the effective ionization, recombination and emission rate coefficients including density effects for H-like and He-like aluminum ions using a collisional radiative model. We calculate time-dependent ion abundances using these effective ionization and recombination rate coefficients. The time-dependent electron temperature and density used in the calculation are based on an analytical model for the hydrodynamic expansion of the target foils. During the laser pulse the target is ionized. After the laser heating stops, the plasma begins to recombine. Using the calculated time dependent ion abundances and the effective emission rate coefficients, we calculate the time dependent Ly{alpha} and He{alpha} lines. The calculations reproduce the main qualitative features of the experimental spectra. (author)

Prepulse suppression using a self-induced, ultrashort pulse plasma mirror

International Nuclear Information System (INIS)

Gold, D.M.; Nathel, H.; Bolton, P.R.; White, W.E.; Van Woerkom, L.D.

1991-01-01

The plasma mirror is a self-induced, plasm-based optical element which can be inserted into existing experiments to reduce repulse energy without significant degradation of ultrashort pulse laser light. The authors have characteristics of the reflected pulse. The initial measurements indicate that the incident pulse reflects specularly from a high density, highly reflective plasma. The reflected pulse has a smoothed spatial profile and reduced pulsewidth. This paper outlines future work to characterize both the plasm mirror technique of repulse suppression and its reflected pulse

On-the-fly depth profiling during ablation with ultrashort laser pulses: A tool for accurate micromachining and laser surgery

International Nuclear Information System (INIS)

Lausten, Rune; Balling, Peter

2001-01-01

A method for accurate depth profiling of a region subjected to ablation with ultrashort laser pulses is demonstrated. Time-gated imaging of the backscattered radiation from the ablation region is performed in a geometry, which allows the depth along a chosen axis on the sample to be determined with a single measurement. The profiling system has a spatial resolution of a few micrometers and applications are promoted by the fact that the measurement is performed with the same pulse that undertakes ablation. This also indicates that the method is inherently suited for in situ on-the-fly measurements. Copyright 2001 American Institute of Physics

High-throughput machining using a high-average power ultrashort pulse laser and high-speed polygon scanner

Science.gov (United States)

Schille, Joerg; Schneider, Lutz; Streek, André; Kloetzer, Sascha; Loeschner, Udo

2016-09-01

High-throughput ultrashort pulse laser machining is investigated on various industrial grade metals (aluminum, copper, and stainless steel) and Al2O3 ceramic at unprecedented processing speeds. This is achieved by using a high-average power picosecond laser in conjunction with a unique, in-house developed polygon mirror-based biaxial scanning system. Therefore, different concepts of polygon scanners are engineered and tested to find the best architecture for high-speed and precision laser beam scanning. In order to identify the optimum conditions for efficient processing when using high-average laser powers, the depths of cavities made in the samples by varying the processing parameter settings are analyzed and, from the results obtained, the characteristic removal values are specified. For overlapping pulses of optimum fluence, the removal rate is as high as 27.8 mm3/min for aluminum, 21.4 mm3/min for copper, 15.3 mm3/min for stainless steel, and 129.1 mm3/min for Al2O3, when a laser beam of 187 W average laser powers irradiates. On stainless steel, it is demonstrated that the removal rate increases to 23.3 mm3/min when the laser beam is very fast moving. This is thanks to the low pulse overlap as achieved with 800 m/s beam deflection speed; thus, laser beam shielding can be avoided even when irradiating high-repetitive 20-MHz pulses.

Dynamics of the spectral behaviour of an ultrashort laser pulse in an argon-gas-filled capillary discharge-preformed plasma channel

Directory of Open Access Journals (Sweden)

Sakai S.

2013-11-01

Full Text Available We have reported the argon plasma waveguide produced in an alumina (Al2O3 capillary discharge and used to guide ultrashort laser pulses at intensities of the order of 1016  W/cm2. A one-dimensional magnetohydrodynamic (MHD code was used to evaluate the average degree of ionization of Ar in the preformed plasma channel. The spectrum of the propagated laser pulse in the Ar plasma waveguide was not modified and was well reproduced by a particle-in-cell (PIC simulation under initial ion charge state of Ar3+ in the preformed plasma waveguide. The optimum timing for the laser pulse injection was around 150 ns after initiation of a discharge with a peak current of 200 A.

Investigation of Temperature Change under Influence of Ultrashort Laser Pulses Taking into Account Relaxation Properties of Materials

Science.gov (United States)

Eremin, A. V.; Kudinov, V. A.; Stefanyuk, E. V.; Kudinov, I. V.

2018-03-01

By using the modified Fourier law’s formula considering the relaxation of heat flow and temperature gradient, a mathematical model of the local non-equilibrium process of plate heating with ultrashort laser pulses was developed. The research showed that consideration of non-locality results in the delayed plate heat up irrespective of the laser radiation flow intensity. It was also shown that in consideration of the relaxation phenomena, the boundary conditions may not be fulfilled immediately – they may be set only within a definite range of the initial time.

Single-pass, efficient type-I phase-matched frequency doubling of high-power ultrashort-pulse Yb-fiber laser using LiB_3O_5

Science.gov (United States)

Shukla, Mukesh Kumar; Kumar, Samir; Das, Ritwick

2016-05-01

We report 48 % efficient single-pass second harmonic generation of high-power ultrashort-pulse ({≈ }250 fs) Yb-fiber laser by utilizing type-I phase matching in LiB_3O_5 (LBO) crystal. The choice of LBO among other borate crystals for high-power frequency doubling is essentially motivated by large thermal conductivity, low birefringence and weak group velocity dispersion. By optimally focussing the beam in a 4-mm-long LBO crystal, we have generated about 2.3 W of average power at 532 nm using 4.8 W of available pump power at 1064 nm. The ultrashort green pulses were found out to be near-transform limited sech^2 pulses with a pulse width of Δ τ ≈ 150 fs and being delivered at 78 MHz repetition rate. Due to appreciably low spatial walk-off angle for LBO ({≈ }0.4°), we obtain M^2beam which signifies marginal distortion in comparison with the pump beam (M^2<1.15). We also discuss the impact of third-order optical nonlinearity of the LBO crystal on the generated ultrashort SH pulses.

Ultra-Short Laser Absorption In Solid Targets

International Nuclear Information System (INIS)

Harfouche, A.; Bendib, A.

2008-01-01

With the rapid development and continuously improving technology of subpicosecond laser pulse generation, new interesting physical problems are now investigated. Among them the laser light absorption in solid targets. During the interaction with solid targets, high intensity laser pulses are absorbed by electrons in optical skin depths, leading to rapid ionization before that significant ablation of solid material takes place. The ultra-short laser is absorbed in the overdense plasma through the electron-ion collisions (normal skin effect) or collisionless mechanisms (anomalous skin effect or sheath inverse bremsstrahlung). These two regimes depend on the laser intensity, the plasma temperature and the ionization state Z. In this work we solve numerically the Fokker-Planck equation to compute the electron distribution function in the skin layer. In the second step we compute the surface impedance and we deduce the absorption coefficient.

Ultrashort pulse shaping by optical parametric chirped amplification

International Nuclear Information System (INIS)

Nelet, Ambre

2007-01-01

The aim of this work is to propose new laser architectures based on optical parametric chirped pulse amplification (OPCPA). Common goals of OPCPA pre-amplifiers are to reach high energy level while maintaining the spectrum width and to adapt geometry of the amplified beam to the high power laser chain optics. We consider OPCPA as a way to control and to sculpt ultrashort pulses. Our first set-up aims at thwarting possible time recovery default between pump and signal pulses, which lower the energy extraction. A regenerative OPCPA, idler resonant, is a way to produce a high-intensity and high-repetition rate train of amplified signal replicas. Our second laser system pre-compensates the spectral gain narrowing by sculpting pulses directly within the OPCPA section, where a temporal shaping of the pump beam permits a spectro-spectral shaping of the amplified signal. Finally, we propose an OPCPA based on spatial coding and uniform amplification of spectral signal components by using a fan-out periodically poled crystal and a zero dispersion line. (author) [fr

High-power ultrashort fiber laser for solar cells micromachining

Science.gov (United States)

Lecourt, J.-B.; Duterte, C.; Liegeois, F.; Lekime, D.; Hernandez, Y.; Giannone, D.

2012-02-01

We report on a high-power ultra-short fiber laser for thin film solar cells micromachining. The laser is based on Chirped Pulse Amplification (CPA) scheme. The pulses are stretched to hundreds of picoseconds prior to amplification and can be compressed down to picosecond at high energy. The repetition rate is adjustable from 100 kHz to 1 MHz and the optical average output power is close to 13 W (before compression). The whole setup is fully fibred, except the compressor achieved with bulk gratings, resulting on a compact and reliable solution for cold ablation.

Polarized spectral properties of Yb3+ : Li2Gd4(MoO4)7 crystal: a candidate for tunable and ultrashort pulse lasers

International Nuclear Information System (INIS)

Zhu Haomiao; Chen Yujin; Lin Yanfu; Gong Xinghong; Liao Jinsheng; Chen Xueyuan; Luo Zundu; Huang Yidong

2007-01-01

Detailed polarized spectral properties of a 3.2 at.% Yb 3+ : Li 2 Gd 4 (MoO 4 ) 7 crystal, including absorption cross-section, emission cross-section, up-conversion spectrum and intrinsic fluorescence lifetime, were investigated. The laser potentiality was also evaluated and the results show that this crystal is a good candidate for tunable and ultrashort pulse lasers

Coherent Control of Multiphoton Transitions in the Gas and Condensed Phases with Shaped Ultrashort Pulses

International Nuclear Information System (INIS)

Dantus, Marcos

2008-01-01

Controlling laser-molecule interactions has become an integral part of developing devices and applications in spectroscopy, microscopy, optical switching, micromachining and photochemistry. Coherent control of multiphoton transitions could bring a significant improvement of these methods. In microscopy, multi-photon transitions are used to activate different contrast agents and suppress background fluorescence; coherent control could generate selective probe excitation. In photochemistry, different dissociative states are accessed through two, three, or more photon transitions; coherent control could be used to select the reaction pathway and therefore the yield-specific products. For micromachining and processing a wide variety of materials, femtosecond lasers are now used routinely. Understanding the interactions between the intense femtosecond pulse and the material could lead to technologically important advances. Pulse shaping could then be used to optimize the desired outcome. The scope of our research program is to develop robust and efficient strategies to control nonlinear laser-matter interactions using ultrashort shaped pulses in gas and condensed phases. Our systematic research has led to significant developments in a number of areas relevant to the AMO Physics group at DOE, among them: generation of ultrashort phase shaped pulses, coherent control and manipulation of quantum mechanical states in gas and condensed phases, behavior of isolated molecules under intense laser fields, behavior of condensed phase matter under intense laser field and implications on micromachining with ultrashort pulses, coherent control of nanoparticles their surface plasmon waves and their nonlinear optical behavior, and observation of coherent Coulomb explosion processes at 10 16 W/cm 2 . In all, the research has resulted in 36 publications (five journal covers) and nine invention disclosures, five of which have continued on to patenting

Characterization of ultrashort laser pulses employing self-phase modulation dispersion-scan technique

Science.gov (United States)

Sharba, A. B.; Chekhlov, O.; Wyatt, A. S.; Pattathil, R.; Borghesi, M.; Sarri, G.

2018-03-01

We present a new phase characterization technique for ultrashort laser pulses that employs self-phase modulation (SPM) in the dispersion scan approach. The method can be implemented by recording a set of nonlinearly modulated spectra generated with a set of known chirp values. The unknown phase of the pulse is retrieved by linking the recorded spectra to the initial spectrum of the pulse via a phase function guessed by a function minimization iterative algorithm. This technique has many advantages over the dispersion scan techniques that use frequency conversion processes. Mainly, the use of SPM cancels out the phase and group velocity mismatch errors and dramatically widens the spectral acceptance of the nonlinear medium and the range of working wavelength. The robustness of the technique is demonstrated with smooth and complex phase retrievals using numerical examples. The method is shown to be not affected by the spatial distribution of the beam or the presence of nonlinear absorption process. In addition, we present an efficient method for phase representation based on a summation of a set of Gaussian functions. The independence of the functions from each other prevents phase coupling of any kind and facilitates a flexible phase representation.

Laser wakefield electron acceleration. A novel approach employing supersonic microjets and few-cycle laser pulses

International Nuclear Information System (INIS)

Schmid, Karl

2011-01-01

This thesis covers the few-cycle laser-driven acceleration of electrons in a laser-generated plasma. This process, known as laser wakefield acceleration (LWFA), relies on strongly driven plasma waves for the generation of accelerating gradients in the vicinity of several 100 GV/m, a value four orders of magnitude larger than that attainable by conventional accelerators. This thesis demonstrates that laser pulses with an ultrashort duration of 8 fs and a peak power of 6 TW allow the production of electron energies up to 50 MeV via LWFA. The special properties of laser accelerated electron pulses, namely the ultrashort pulse duration, the high brilliance, and the high charge density, open up new possibilities in many applications of these electron beams. (orig.)

Multifunctional gold nanorods for selective plasmonic photothermal therapy in pancreatic cancer cells using ultra-short pulse near-infrared laser irradiation.

Science.gov (United States)

Patino, Tania; Mahajan, Ujjwal; Palankar, Raghavendra; Medvedev, Nikolay; Walowski, Jakob; Münzenberg, Markus; Mayerle, Julia; Delcea, Mihaela

2015-03-12

Gold nanorods (AuNRs) have attracted considerable attention in plasmonic photothermal therapy for cancer treatment by exploiting their selective and localized heating effect due to their unique photophysical properties. Here we describe a strategy to design a novel multifunctional platform based on AuNRs to: (i) specifically target the adenocarcinoma MUC-1 marker through the use of the EPPT-1 peptide, (ii) enhance cellular uptake through a myristoylated polyarginine peptide (MPAP) and (iii) selectively induce cell death by ultra-short near infrared laser pulses. We used a biotin-avidin based approach to conjugate EPPT-1 and MPAP to AuNRs. Dual-peptide (EPPT-1+MPAP) labelled AuNRs showed a significantly higher uptake by pancreatic ductal adenocarcinoma cells when compared to their single peptide or avidin conjugated counterparts. In addition, we selectively induced cell death by ultra-short near infrared laser pulses in small target volumes (∼1 μm3), through the creation of plasmonic nanobubbles that lead to the destruction of a local cell environment. Our approach opens new avenues for conjugation of multiple ligands on AuNRs targeting cancer cells and tumors and it is relevant for plasmonic photothermal therapy.

Non-destructive testing of ceramic materials using mid-infrared ultrashort-pulse laser

Science.gov (United States)

Sun, S. C.; Qi, Hong; An, X. Y.; Ren, Y. T.; Qiao, Y. B.; Ruan, Liming M.

2018-04-01

The non-destructive testing (NDT) of ceramic materials using mid-infrared ultrashort-pulse laser is investigated in this study. The discrete ordinate method is applied to solve the transient radiative transfer equation in 2D semitransparent medium and the emerging radiative intensity on boundary serves as input for the inverse analysis. The sequential quadratic programming algorithm is employed as the inverse technique to optimize objective function, in which the gradient of objective function with respect to reconstruction parameters is calculated using the adjoint model. Two reticulated porous ceramics including partially stabilized zirconia and oxide-bonded silicon carbide are tested. The retrieval results show that the main characteristics of defects such as optical properties, geometric shapes and positions can be accurately reconstructed by the present model. The proposed technique is effective and robust in NDT of ceramics even with measurement errors.

Nonresonant interaction of ultrashort electromagnetic pulses with multilevel quantum systems

Science.gov (United States)

Belenov, E.; Isakov, V.; Nazarkin, A.

1994-01-01

Some features of the excitation of multilevel quantum systems under the action of electromagnetic pulses which are shorter than the inverse frequency of interlevel transitions are considered. It is shown that the interaction is characterized by a specific type of selectivity which is not connected with the resonant absorption of radiation. The simplest three-level model displays the inverse population of upper levels. The effect of an ultrashort laser pulse on a multilevel molecule was regarded as an instant reception of the oscillation velocity by the oscillator and this approach showed an effective excitation and dissociation of the molecule. The estimations testify to the fact that these effects can be observed using modern femtosecond lasers.

Birefringence profile adjustment by spatial overlap of nanogratings induced by ultra-short laser pulses inside fused silica

Science.gov (United States)

Arabanian, Atoosa Sadat; Najafi, Somayeh; Ajami, Aliasghar; Husinsky, Wolfgang; Massudi, Reza

2018-02-01

We have succeeded in realizing a method to control the spatial distribution of optical retardation as a result of nanogratings in bulk-fused silica induced by ultrashort laser pulses. A colorimetry-based retardation measurement (CBRM) based on the Michel-Levy interference color chart using a polarization microscope is used to determine the profiles of the optical retardation. Effects of the spatial overlap of written regions as well as the energy and polarization of the writing pulses on the induced retardations are studied. It has been found that the spatial overlap of lines written by pulse trains with different energies and polarizations can result in an adjustment of the induced birefringence in the overlap region. This approach offers the possibility of designing polarization-sensitive components with a desired birefringence profile.

Ultrashort megaelectronvolt positron beam generation based on laser-accelerated electrons

Science.gov (United States)

Xu, Tongjun; Shen, Baifei; Xu, Jiancai; Li, Shun; Yu, Yong; Li, Jinfeng; Lu, Xiaoming; Wang, Cheng; Wang, Xinliang; Liang, Xiaoyan; Leng, Yuxin; Li, Ruxin; Xu, Zhizhan

2016-03-01

Experimental generation of ultrashort MeV positron beams with high intensity and high density using a compact laser-driven setup is reported. A high-density gas jet is employed experimentally to generate MeV electrons with high charge; thus, a charge-neutralized MeV positron beam with high density is obtained during laser-accelerated electrons irradiating high-Z solid targets. It is a novel electron-positron source for the study of laboratory astrophysics. Meanwhile, the MeV positron beam is pulsed with an ultrashort duration of tens of femtoseconds and has a high peak intensity of 7.8 × 1021 s-1, thus allows specific studies of fast kinetics in millimeter-thick materials with a high time resolution and exhibits potential for applications in positron annihilation spectroscopy.

Interaction of ultra-short ultra-intense laser pulses with under-dense plasmas; Interaction d'impulsions laser ultra-courtes et ultra-intenses avec des plasmas sous denses

Energy Technology Data Exchange (ETDEWEB)

Solodov, A

2000-12-15

Different aspects of interaction of ultra-short ultra-intense laser pulses with underdense plasmas are studied analytically and numerically. These studies can be interesting for laser-driven electron acceleration in plasma, X-ray lasers, high-order harmonic generation, initial confinement fusion with fast ignition. For numerical simulations a fully-relativistic particle code WAKE was used, developed earlier at Ecole Polytechnique. It was modified during the work on the thesis in the part of simulation of ion motion, test electron motion, diagnostics for the field and plasma. The studies in the thesis cover the problems of photon acceleration in the plasma wake of a short intense laser pulse, phase velocity of the plasma wave in the Self-Modulated Laser Wake-Field Accelerator (SM LWFA), relativistic channeling of laser pulses with duration of the order of a plasma period, ion dynamics in the wake of a short intense laser pulse, plasma wave breaking. Simulation of three experiments on the laser pulse propagation in plasma and electron acceleration were performed. Among the main results of the thesis, it was found that reduction of the plasma wave phase velocity in the SM LWFA is crucial for electron acceleration, only if a plasma channel is used for the laser pulse guiding. Self-similar structures describing relativistic guiding of short laser pulses in plasmas were found and relativistic channeling of initially Gaussian laser pulses of a few plasma periods in duration was demonstrated. It was shown that ponderomotive force of a plasma wake excited by a short laser pulse forms a channel in plasma and plasma wave breaking in the channel was analyzed in detail. Effectiveness of electron acceleration by the laser field and plasma wave was compared and frequency shift of probe laser pulses by the plasma waves was found in conditions relevant to the current experiments. (author)

The time resolved measurement of ultrashort terahertz-band electric fields without an ultrashort probe

International Nuclear Information System (INIS)

Walsh, D. A.; Snedden, E. W.; Jamison, S. P.

2015-01-01

The time-resolved detection of ultrashort pulsed THz-band electric field temporal profiles without an ultrashort laser probe is demonstrated. A non-linear interaction between a narrow-bandwidth optical probe and the THz pulse transposes the THz spectral intensity and phase information to the optical region, thereby generating an optical pulse whose temporal electric field envelope replicates the temporal profile of the real THz electric field. This optical envelope is characterised via an autocorrelation based FROG (frequency resolved optical gating) measurement, hence revealing the THz temporal profile. The combination of a narrow-bandwidth, long duration, optical probe, and self-referenced FROG makes the technique inherently immune to timing jitter between the optical probe and THz pulse and may find particular application where the THz field is not initially generated via ultrashort laser methods, such as the measurement of longitudinal electron bunch profiles in particle accelerators

Using a fast dual-wavelength imaging ellipsometric system to measure the flow thickness profile of an oil thin film

Science.gov (United States)

Kuo, Chih-Wei; Han, Chien-Yuan; Jhou, Jhe-Yi; Peng, Zeng-Yi

2017-11-01

Dual-wavelength light sources with stroboscopic illumination technique were applied in a process of photoelastic modulated ellipsometry to retrieve two-dimensional ellipsometric parameters of thin films on a silicon substrate. Two laser diodes were alternately switched on and modulated by a programmable pulse generator to generate four short pulses at specific temporal phase angles in a modulation cycle, and short pulses were used to freeze the intensity variation of the PEM modulated signal that allows ellipsometric images to be captured by a charge-coupled device. Although the phase retardation of a photoelastic modulator is related to the light wavelength, we employed an equivalent phase retardation technique to avoid any setting from the photoelastic modulator. As a result, the ellipsometric parameters of different wavelengths may be rapidly obtained using this dual-wavelength ellipsometric system every 4 s. Both static and dynamic experiments are demonstrated in this work.

Theoretical analysis of supercontinuum and coloured conical emission produced during ultrashort laser pulse interaction with gases

International Nuclear Information System (INIS)

Semak, V V; Shneider, M N

2014-01-01

We use a conceptually new approach to theoretical modelling of self-focusing in which we integrated diffractive and geometrical optics in order to explain and predict emission of white light and coloured rings observed in ultrashort laser pulse interaction. In our approach, laser beam propagation is described by blending the solution of the linear Maxwell's equation and a correction term that represents nonlinear field perturbation expressed in terms of paraxial ray-optics (eikonal) equation. No attempt is made to create an appearance of exhaustive treatment via use of complex mathematical models. Rather, emphasis is placed on elegance of the formulations leading to fundamental understanding of the underlying physics and, eventually, to an accurate practical numerical model capable of simulating white light generation and conical emission of coloured rings produced around the filament. (paper)

Fields of an ultrashort tightly focused radially polarized laser pulse in a linear response plasma

Science.gov (United States)

Salamin, Yousef I.

2017-10-01

Analytical expressions for the fields of a radially polarized, ultrashort, and tightly focused laser pulse propagating in a linear-response plasma are derived and discussed. The fields are obtained from solving the inhomogeneous wave equations for the vector and scalar potentials, linked by the Lorenz gauge, in a plasma background. First, the scalar potential is eliminated using the gauge condition, then the vector potential is synthesized from Fourier components of an initial uniform distribution of wavenumbers, and the inverse Fourier transformation is carried out term-by-term in a truncated series (finite sum). The zeroth-order term in, for example, the axial electric field component is shown to model a pulse much better than its widely used paraxial approximation counterpart. Some of the propagation characteristics of the fields are discussed and all fields are shown to have manifested the expected limits for propagation in a vacuum.

Signatures of collective electron dynamics in the angular distributions of electrons ejected during ultrashort laser pulse interactions with C+

International Nuclear Information System (INIS)

Lysaght, M A; Hutchinson, S; Van der Hart, H W

2009-01-01

We use the time-dependent R-matrix approach to investigate an ultrashort pump-probe scheme to observe collective electron dynamics in C + driven by the repulsion of two equivalent p electrons. By studying the two-dimensional momentum distributions of the ejected electron as a function of the time-delay between an ultrashort pump pulse and an ionizing ultrashort probe pulse it is possible to track the collective dynamics inside the C + ion in the time domain.

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.

Innovation: study of 'ultra-short' time reactions

International Nuclear Information System (INIS)

Anon.

2001-01-01

This short article presents the new Elyse facility of Orsay-Paris 11 university for the study of ultra-short chemical and biochemical phenomena. Elyse uses the 'pump-probe' technique which consists in two perfectly synchronized electron and photon pulses. It comprises a 3 to 9 MeV electron accelerator with a HF gun photo-triggered with a laser. Elyse can initiate reactions using ultra-short electron pulses (radiolysis) or ultra-short photon pulses (photolysis). (J.S.)

Radiobiological response to ultra-short pulsed megavoltage electron beams of ultra-high pulse dose rate.

Science.gov (United States)

Beyreuther, Elke; Karsch, Leonhard; Laschinsky, Lydia; Leßmann, Elisabeth; Naumburger, Doreen; Oppelt, Melanie; Richter, Christian; Schürer, Michael; Woithe, Julia; Pawelke, Jörg

2015-08-01

In line with the long-term aim of establishing the laser-based particle acceleration for future medical application, the radiobiological consequences of the typical ultra-short pulses and ultra-high pulse dose rate can be investigated with electron delivery. The radiation source ELBE (Electron Linac for beams with high Brilliance and low Emittance) was used to mimic the quasi-continuous electron beam of a clinical linear accelerator (LINAC) for comparison with electron pulses at the ultra-high pulse dose rate of 10(10) Gy min(-1) either at the low frequency of a laser accelerator or at 13 MHz avoiding effects of prolonged dose delivery. The impact of pulse structure was analyzed by clonogenic survival assay and by the number of residual DNA double-strand breaks remaining 24 h after irradiation of two human squamous cell carcinoma lines of differing radiosensitivity. The radiation response of both cell lines was found to be independent from electron pulse structure for the two endpoints under investigation. The results reveal, that ultra-high pulse dose rates of 10(10) Gy min(-1) and the low repetition rate of laser accelerated electrons have no statistically significant influence (within the 95% confidence intervals) on the radiobiological effectiveness of megavoltage electrons.

Ultrashort pulsed laser technology development program

Science.gov (United States)

Manke, Gerald C.

2014-10-01

The Department of Navy has been pursuing a technology development program for advanced, all-fiber, Ultra Short Pulsed Laser (USPL) systems via Small Business Innovative Research (SBIR) programs. Multiple topics have been published to promote and fund research that encompasses every critical component of a standard USPL system and enable the demonstration of mJ/pulse class systems with an all fiber architecture. This presentation will summarize published topics and funded programs.

Comparison of soft and hard tissue ablation with sub-ps and ns pulse lasers

Energy Technology Data Exchange (ETDEWEB)

Da Silva, L.B.; Stuart, B.C.; Celliers, P.M.; Feit, M.D.; Glinsky, M.E.; Heredia, N.J.; Herman, S.; Lane, S.M.; London, R.A.; Matthews, D.L.; Perry, M.D.; Rubenchik, A.M. [Lawrence Livermore National Lab., CA (United States); Chang, T.D. [Veterans Administration Hospital, Martinez, CA (United States); Neev, J. [Beckman Laser Inst. and Medical Clinic, Irvine, CA (United States)

1996-05-01

Tissue ablation with ultrashort laser pulses offers several unique advantages. The nonlinear energy deposition is insensitive to tissue type, allowing this tool to be used for soft and hard tissue ablation. The localized energy deposition lead to precise ablation depth and minimal collateral damage. This paper reports on efforts to study and demonstrate tissue ablation using an ultrashort pulse laser. Ablation efficiency and extent of collateral damage for 0.3 ps and 1000 ps duration laser pulses are compared. Temperature measurements of the rear surface of a tooth section is also presented.

Selective ablation of a titanium nitride film on tungsten carbide substrate using ultrashort laser pulses

International Nuclear Information System (INIS)

Oliveira, Eduardo Spinelli

2017-01-01

Surface coatings are applied to many cutting tools in the metallurgical industry in order to improve cutting efficiency and extend its useful life. In this work, tests were performed to remove the coating of titanium aluminum nitride (TiAlN) on tungsten carbide (WC-Co) pellets, using an ultrashort laser pulses beam. After determination of the damage thresholds of the film and the substrate, were ablated on the surface of the coating lines using two ablation conditions, it was initially operated on the low fluence regime for the film, and later on the low fluence regime of the substrate, far below the threshold of the film, applying high overlapping pulses. A laser induced breakdown spectroscopy (LIBS) system was set up to monitor the materials present in the plasma generated by the laser, but the system did not present sufficient sensitivity to read the low intensity of the plasma generated in the process and was not used. After the analysis of the traces by electron microscopy, optical profilometer and X-ray fluorescence spectroscopy, it was not possible to determine a safe process to carry out the selective removal of the film in question, however, due to the data obtained and observations of the results in some traces, new possibilities were raised, opening the discussion for future work. (author)

Heat generation caused by ablation of dental hard tissues with an ultrashort pulse laser (USPL) system.

Science.gov (United States)

Braun, Andreas; Krillke, Raphael Franz; Frentzen, Matthias; Bourauel, Christoph; Stark, Helmut; Schelle, Florian

2015-02-01

Heat generation during the removal of dental hard tissues may lead to a temperature increase and cause painful sensations or damage dental tissues. The aim of this study was to assess heat generation in dental hard tissues following laser ablation using an ultrashort pulse laser (USPL) system. A total of 85 specimens of dental hard tissues were used, comprising 45 specimens of human dentine evaluating a thickness of 1, 2, and 3 mm (15 samples each) and 40 specimens of human enamel with a thickness of 1 and 2 mm (20 samples each). Ablation was performed with an Nd:YVO4 laser at 1,064 nm, a pulse duration of 9 ps, and a repetition rate of 500 kHz with an average output power of 6 W. Specimens were irradiated for 0.8 s. Employing a scanner system, rectangular cavities of 1-mm edge length were generated. A temperature sensor was placed at the back of the specimens, recording the temperature during the ablation process. All measurements were made employing a heat-conductive paste without any additional cooling or spray. Heat generation during laser ablation depended on the dental hard tissue (enamel or dentine) and the thickness of the respective tissue (p dental hard tissues, heat generation has to be considered. Especially during laser ablation next to pulpal tissues, painful sensations and potential thermal injury of pulp tissue might occur.

Ionization of a multilevel atom by ultrashort laser pulses

International Nuclear Information System (INIS)

Andreev, A. V.; Stremoukhov, S. Yu.; Shutova, O. A.

2010-01-01

Specific features of ionization of single atoms by laser fields of a near-atomic strength are investigated. Calculations are performed for silver atoms interacting with femtosecond laser pulses with wavelengths λ = 800 nm (Ti:Sapphire) and λ = 1.064 μm (Nd:YAG). The dependences of the probability of ionization and of the form of the photoelectron energy spectra on the field of laser pulses for various values of their duration are considered. It is shown that the behavior of the probability of ionization in the range of subatomic laser pulse fields is in good agreement with the Keldysh formula. However, when the field strength attains values close to the atomic field strength, the discrepancies in these dependences manifested in a decrease in the ionization rate (ionization stabilization effect) or in its increase (accelerated ionization) are observed. These discrepancies are associated with the dependence of the population dynamics of excited discrete energy levels of the atom on the laser pulse field amplitude.

Hydrodynamic model for ultra-short pulse ablation of hard dental tissue

Energy Technology Data Exchange (ETDEWEB)

London, R.A.; Bailey, D.S.; Young, D.A.; Alley, W.E.; Feit, M.D.; Rubenchik, A.M. [Lawrence Livermore National Lab., CA (United States); Neev, J. [Beckman Laser Inst., Irvine, CA (United States)

1996-02-29

A computational model for the ablation of tooth enamel by ultra-short laser pulses is presented. The role of simulations using this model in designing and understanding laser drilling systems is discussed. Pulses of duration 300 fsec and intensity greater than 10{sup 12} W/cm{sup 2} are considered. Laser absorption proceeds via multi-photon initiated plasma mechanism. The hydrodynamic response is calculated with a finite difference method, using an equation of state constructed from thermodynamic functions including electronic, ion motion, and chemical binding terms. Results for the ablation efficiency are presented. An analytic model describing the ablation threshold and ablation depth is presented. Thermal coupling to the remaining tissue and long-time thermal conduction are calculated. Simulation results are compared to experimental measurements of the ablation efficiency. Desired improvements in the model are presented.

Applications of ultrashort shaped pulses in microscopy and for controlling chemical reactions

International Nuclear Information System (INIS)

Lozovoy, Vadim V.; Andegeko, Yair; Zhu Xin; Dantus, Marcos

2008-01-01

This article presents a new perspective on laser control based on insights into the effect of spectral phase on nonlinear optical processes. Gaining this understanding requires the systematic evaluation of the molecular response as a function of a series of pre-defined accurately shaped laser pulses. The effort required is rewarded with robust, highly reproducible, results. This approach is illustrated by results on selective two-photon excitation microscopy of biological samples, where higher signal and less photobleaching damage are achieved by accurate phase measurement and elimination of high-order phase distortions from the ultrashort laser pulses. A similar systematic approach applied to laser control of gas phase chemical reactions reveals surprising general trends. Molecular fragmentation pattern is found to be dependent on phase shaping. Differently shaped pulses with similar pulse duration have been found to produce similar fragmentation patterns. This implies that any single parameter that is proportional to the pulse duration, such as second harmonic generation intensity, allows us to predict the molecular fragmentation pattern within the experimental noise. This finding, is illustrated here for a series of isomers. Bond selectivity, coherent photochemistry and their applications are discussed in light of results from these systematic studies

Propagation of femtosecond laser pulses through water in the linear absorption regime.

Science.gov (United States)

Naveira, Lucas M; Strycker, Benjamin D; Wang, Jieyu; Ariunbold, Gombojav O; Sokolov, Alexei V; Kattawar, George W

2009-04-01

We investigate the controversy regarding violations of the Bouguer-Lambert-Beer (BLB) law for ultrashort laser pulses propagating through water. By working at sufficiently low incident laser intensities, we make sure that any nonlinear component in the response of the medium is negligible. We measure the transmitted power and spectrum as functions of water cell length in an effort to confirm or disprove alleged deviations from the BLB law. We perform experiments at two different laser pulse repetition rates and explore the dependence of transmission on pulse duration. Specifically, we vary the laser pulse duration either by cutting its spectrum while keeping the pulse shape near transform-limited or by adjusting the pulses chirp while keeping the spectral intensities fixed. Over a wide range of parameters, we find no deviations from the BLB law and conclude that recent claims of BLB law violations are inconsistent with our experimental data. We present a simple linear theory (based on the BLB law) for propagation of ultrashort laser pulses through an absorbing medium and find our experimental results to be in excellent agreement with this theory.

Pulsed laser ablation and deposition of niobium carbide

International Nuclear Information System (INIS)

Sansone, M.; De Bonis, A.; Santagata, A.; Rau, J.V.; Galasso, A.; Teghil, R.

2016-01-01

Highlights: • We have deposited in vacuum niobium carbide films by fs and ns PLD. • We have compared PLD performed by ultra-short and short laser pulses. • The films deposited by fs PLD of NbC are formed by nanoparticles. • The structure of the films produced by fs PLD at 500 °C corresponds to NbC. - Abstract: NbC crystalline films have been deposited in vacuum by ultra-short pulsed laser deposition technique. The films have been characterized by transmission and scanning electron microscopies and by X-ray diffraction. To clarify the ablation–deposition mechanism, the plasma produced by the ablation process has been characterized by optical emission spectroscopy and fast imaging. A comparison of the results with those obtained by ns pulsed deposition of the same target has been carried out.

Electron in the ultrashort laser pulse

Czech Academy of Sciences Publication Activity Database

Pardy, Miroslav

2003-01-01

Roč. 42, č. 1 (2003), s. 99-110 ISSN 0020-7748 R&D Projects: GA MŠk LN00A100 Institutional research plan: CEZ:AV0Z2043910 Keywords : laser pulse, Volkov solution, compton effect Subject RIV: BE - The oretical Physics Impact factor: 0.476, year: 2003

Scattering of Femtosecond Laser Pulses on the Negative Hydrogen Ion

Science.gov (United States)

Astapenko, V. A.; Moroz, N. N.

2018-05-01

Elastic scattering of ultrashort laser pulses (USLPs) on the negative hydrogen ion is considered. Results of calculations of the USLP scattering probability are presented and analyzed for pulses of two types: the corrected Gaussian pulse and wavelet pulse without carrier frequency depending on the problem parameters.

Half-period optical pulse generation using a free-electron laser

International Nuclear Information System (INIS)

Jaroszynski, D.A.; Chaix, P.; Piovella, N.

1995-01-01

Recently there has been growth, in interest in non-equilibrium interaction of half-period long optical pulses with matter. To date the optical pulses have been produced by chopping out a half-period long segment from a longer pulse using a semiconductor switch driven by a femtosecond laser. In this paper we present new methods for producing tunable ultra-short optical pulses as short as half an optical period using a free-electron laser driven by electron bunches with a duration a fraction of an optical period. Two different methods relying on the production of coherent spontaneous emission will be described. In the first method we show that when a train of ultra-short optical pulses as short as one half period. We present calculations which show that the small signal gain is unimportant in the early stages of radiation build up in the cavity when the startup process is dominated by coherent spontaneous emission. To support our proposed method we present encouraging experimental results from the FELIX experiment in the Netherlands which show that interference effects between the coherent spontaneous optical pulses at start-up are very important. The second proposed method relies on the fact that coherent spontaneous emission mimics the undulations of electrons as they pass through the undulator. We show that ultra-short optical pulses are produced by coherent spontaneous emission when ultra-short electron bunches pass through an ultra-short undulator. We discuss the interesting case of such undulator radiation in the presence of an optical cavity and show that the optical pulse can be open-quotes tayloredclose quotes by simply adjusting the optical cavity desynchronism. The proposed methods may be realisable using existing rf driven FELs in the far-infrared

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.

Texturing in titanium grade 2 surface irradiate with ultrashort pulse laser; Texturizacao em superficies de titanio grau 2 irradiadas com laser com pulsos ultracurtos

Energy Technology Data Exchange (ETDEWEB)

Nogueira, Alessandro Francelino

2015-07-01

The texturing laser micromachining is an important alternative to improve the bonding adhesion between composites and titanium, which are applied to structural components in the aerospace industry. The texturing running on titanium plates is due to the fact that the preferred joining technique for many composite materials is the adhesive bonding. In this work, titanium plates were texturized using laser ultrashort pulses temporal widths of femtoseconds. This process resulted in minimal heat transfer to the material, avoiding deformation of the titanium plate surface as well as the formation of resolidified material in the ablated region. These drawbacks have occurred with the use of nanoseconds pulses. Were performed three types of texturing using laser with femtosecond pulses, with variations in the distances between the machined lines. The analysis of the obtained surfaces found that the wettability increases when there is the increased distance between the texturing lines. Advancing in the analysis by optical profilometry of textured surfaces was observed that there is substantial increase in the volume available for penetration of structural adhesive when the distances between the textured lines are diminished. In tensile tests conducted it was observed that there is an increase in shear strength of the adhesive joint by reducing the distance between the textured lines. (author)

Ultrashort pulse laser deposition of thin films

Science.gov (United States)

Perry, Michael D.; Banks, Paul S.; Stuart, Brent C.

2002-01-01

Short pulse PLD is a viable technique of producing high quality films with properties very close to that of crystalline diamond. The plasma generated using femtosecond lasers is composed of single atom ions with no clusters producing films with high Sp.sup.3 /Sp.sup.2 ratios. Using a high average power femtosecond laser system, the present invention dramatically increases deposition rates to up to 25 .mu.m/hr (which exceeds many CVD processes) while growing particulate-free films. In the present invention, deposition rates is a function of laser wavelength, laser fluence, laser spot size, and target/substrate separation. The relevant laser parameters are shown to ensure particulate-free growth, and characterizations of the films grown are made using several diagnostic techniques including electron energy loss spectroscopy (EELS) and Raman spectroscopy.

Generalized bipolariton model. propagation of a ultrashort laser pulse through a thin semiconductor film in the conditions of two-photon generation of biexcitons

International Nuclear Information System (INIS)

Igor Beloussov

2013-01-01

A generalized bipolariton model is proposed. Bipolaritons is formed from virtual excitons of four kinds. There exists both attractive and repulsive interaction between these excitons, though only excitons of a specific type can interact with light. A substantial difference between conventional and our models is shown for the case of nonlinear transmission/reflection of ultrashort laser pulses by a thin semiconductor film under two-photon generation of biexcitons. (author)

Mid-infrared beam splitter for ultrashort pulses.

Science.gov (United States)

Somma, Carmine; Reimann, Klaus; Woerner, Michael; Kiel, Thomas; Busch, Kurt; Braun, Andreas; Matalla, Mathias; Ickert, Karina; Krüger, Olaf

2017-08-01

A design is presented for a beam splitter suitable for ultrashort pulses in the mid-infrared and terahertz spectral range consisting of a structured metal layer on a diamond substrate. Both the theory and experiment show that this beam splitter does not distort the temporal pulse shape.

Improved ultrashort pulse-retrieval algorithm for frequency-resolved optical gating

International Nuclear Information System (INIS)

DeLong, K.W.; Trebino, R.

1994-01-01

We report on significant improvements in the pulse-retrieval algorithm used to reconstruct the amplitude and the phase of ultrashort optical pulses from the experimental frequency-resolved optical gating trace data in the polarization-gate geometry. These improvements involve the use of an intensity constraint, an overcorrection technique, and a multidimensional minimization scheme. While the previously published, basic algorithm converged for most common ultrashort pulses, it failed to retrieve pulses with significant intensity substructure. The improved composite algorithm successfully converges for such pulses. It can now retrieve essentially all pulses of practical interest. We present examples of complex waveforms that were retrieved by the improved algorithm

Strong-field QED processes in short laser pulses. One- and two-photon Compton scattering

Energy Technology Data Exchange (ETDEWEB)

Seipt, Daniel

2012-12-20

The purpose of this thesis is to advance the understanding of strong-field QED processes in short laser pulses. The processes of non-linear one-photon and two-photon Compton scattering are studied, that is the scattering of photons in the interaction of relativistic electrons with ultra-short high-intensity laser pulses. These investigations are done in view of the present and next generation of ultra-high intensity optical lasers which are supposed to achieve unprecedented intensities of the order of 10{sup 24} W/cm{sup 2} and beyond, with pulse lengths in the order of some femtoseconds. The ultra-high laser intensity requires a non-perturbative description of the interaction of charged particles with the laser field to allow for multi-photon interactions, which is beyond the usual perturbative expansion of QED organized in powers of the fine structure constant. This is achieved in strong-field QED by employing the Furry picture and non-perturbative solutions of the Dirac equation in the presence of a background laser field as initial and final state wave functions, as well as the laser dressed Dirac-Volkov propagator. The primary objective is a realistic description of scattering processes with regard to the finite laser pulse duration beyond the common approximation of infinite plane waves, which is made necessary by the ultra-short pulse length of modern high-intensity lasers. Non-linear finite size effects are identified, which are a result of the interplay between the ultra-high intensity and the ultra-short pulse length. In particular, the frequency spectra and azimuthal photon emission spectra are studied emphasizing the differences between pulsed and infinite laser fields. The proper description of the finite temporal duration of the laser pulse leads to a regularization of unphysical infinities (due to the infinite plane-wave description) of the laser-dressed Dirac-Volkov propagator and in the second-order strong-field process of two-photon Compton

Emission and electron transitions in an atom interacting with an ultrashort electromagnetic pulse

International Nuclear Information System (INIS)

Matveev, V.I.

2003-01-01

Electron transitions and emission of an atom interacting with a spatially inhomogeneous ultrashort electromagnetic pulse are considered. The excitation and ionization probabilities are obtained as well as the spectra and cross sections of the reemission of such a pulse by atoms. By way of an example, one- and two-electron inelastic processes accompanying the interaction of ultrashort pulses with hydrogen- and helium-like atoms are considered. The developed technique makes it possible to take into account exactly the spatial nonuniformity of the ultrashort pulse field and photon momenta in the course of reemission

Variational analysis of self-focusing of intense ultrashort pulses in gases

International Nuclear Information System (INIS)

Arevalo, E.; Becker, A.

2005-01-01

By using perturbation theory we derive an expression for the electrical field of a Gaussian laser beam propagating in a gas medium. This expression is used as a trial solution in a variational method to get quasianalytical solutions for the width, intensity, and self-focusing distance. The approximation gives a better agreement with results of numerical simulations for a broad range of values of the input power than previous analytical results available in the literature. The results apply in the case of ultrashort pulses too

Application of the ultrashort pulses in bovine dental enamel

International Nuclear Information System (INIS)

Todescan, Carla de Rago

2003-01-01

The interaction of lasers with the hard structures of the teeth, has found the excess of heat as a problem for its utilization. This study analyzes, in vitro, the interaction of the ultrashort pulse laser of Ti:safire (830 nm) with the bovine dental enamel. The system consisted in one main oscillator integrated with an amplifier (CPA). The pulses extracted before the temporal compression inside the amplifier had 30 ps, 1000 Hz and ∼1 mJ. The pulses extracted after the compression had 60 fs, 1000 Hz and ∼0,7 mJ. The M 2 was 1,3, the focal lens 2,5 cm, the focal distance 29,7 and a computerized translation stage x,y,z. We evaluated the amount of tissue removed per pulse,the resulting cavities and the surrounding tissues not irradiated, under OM and SEM. The fluency was the major factor for differentiating the two regimens studied, therefore, the intensity was not so important as we expected in this process. We found: one ablation region in 'cat tongue', one ablation length, one fluency ∼0,7 J/cm 2 for 30 ps and ∼0,5 J/cm 2 for 60 fs (50% of high speed burr), smooth edge for 30 ps and high precision of the sharp edge cut of submicrometric order for 60 fs. (author)

Modeling short-pulse laser excitation of dielectric materials

DEFF Research Database (Denmark)

Wædegaard, Kristian Juncher; Sandkamm, Ditte Både; Haahr-Lillevang, Lasse

2014-01-01

A theoretical description of ultrashort-pulse laser excitation of dielectric materials based on strong-field excitation in the Keldysh picture combined with a multiple-rateequation model for the electronic excitation including collisional processes is presented. The model includes light attenuation...

Numerical analysis of laser ablation and damage in glass with multiple picosecond laser pulses.

Science.gov (United States)

Sun, Mingying; Eppelt, Urs; Russ, Simone; Hartmann, Claudia; Siebert, Christof; Zhu, Jianqiang; Schulz, Wolfgang

2013-04-08

This study presents a novel numerical model for laser ablation and laser damage in glass including beam propagation and nonlinear absorption of multiple incident ultrashort laser pulses. The laser ablation and damage in the glass cutting process with a picosecond pulsed laser was studied. The numerical results were in good agreement with our experimental observations, thereby revealing the damage mechanism induced by laser ablation. Beam propagation effects such as interference, diffraction and refraction, play a major role in the evolution of the crater structure and the damage region. There are three different damage regions, a thin layer and two different kinds of spikes. Moreover, the electronic damage mechanism was verified and distinguished from heat modification using the experimental results with different pulse spatial overlaps.

Synchronization of sub-picosecond electron and laser pulses

International Nuclear Information System (INIS)

Rosenzweig, J.B.; Le Sage, G.P.

1999-01-01

Sub-picosecond laser-electron synchronization is required to take full advantage of the experimental possibilities arising from the marriage of modern high intensity lasers and high brightness electron beams in the same laboratory. Two particular scenarios stand out in this regard, injection of ultra-short electron pulses in short wavelength laser-driven plasma accelerators, and Compton scattering of laser photons from short electron pulses. Both of these applications demand synchronization, which is sub-picosecond, with tens of femtosecond synchronization implied for next generation experiments. The design of a microwave timing modulator system is now being investigated in more detail. (AIP) copyright 1999 American Institute of Physics

The chirped-pulse inverse free-electron laser: A high-gradient vacuum laser accelerator

International Nuclear Information System (INIS)

Hartemann, F.V.; Landahl, E.C.; Troha, A.L.; Van Meter, J.R.; Baldis, H.A.; Freeman, R.R.; Luhmann, N.C. Jr.; Song, L.; Kerman, A.K.; Yu, D.U.

1999-01-01

The inverse free-electron laser (IFEL) interaction is studied theoretically and computationally in the case where the drive laser intensity approaches the relativistic regime, and the pulse duration is only a few optical cycles long. The IFEL concept has been demonstrated as a viable vacuum laser acceleration process; it is shown here that by using an ultrashort, ultrahigh-intensity drive laser pulse, the IFEL interaction bandwidth and accelerating gradient are increased considerably, thus yielding large energy gains. Using a chirped pulse and negative dispersion focusing optics allows one to take further advantage of the laser optical bandwidth and produce a chromatic line focus maximizing the gradient. The combination of these novel ideas results in a compact vacuum laser accelerator capable of accelerating picosecond electron bunches with a high gradient (GeV/m) and very low energy spread. copyright 1999 American Institute of Physics

Linear and non-linear carrier-envelope phase difference effects in interactions of ultra-short laser pulses with a metal nano-layer

International Nuclear Information System (INIS)

Varro, S.

2006-01-01

Complete test of publication follows. On the basis of classical electrodynamics the reflection and transmission of an ultra-short laser pulse impinging on a metal nano-layer have been analysed. The thickness of the layer was assumed to be of the order of 2-10 nm, and the metallic electrons were represented by a surface current density at the plane boundary of a dielectric substrate. It has been shown that in the scattered fields a non-oscillatory wake-field appears following the main pulse with an exponential decay and with a definite sign of the electric and magnetic fields. The characteristic time of these wake-fields is inversely proportional to the square of the plasma frequency and to the thickness of the metal nano-layer, and can be of order or larger then the original pulse duration. The magnitude of these wake-fields is proportional with the incoming field strength - so this is a linear effect - and the definite sign of them is governed by the cosine of the carrier-envelope phase difference of the incoming ultrashort laser pulse. As a consequence, when we let such a wake-field excite the electrons of a secondary target - say a plasma, a metal surface or a gas - we obtain 100 percent modulation depth in the electron signal in a given direction. This scheme can perhaps serve as a basis for the construction of a robust linear carrier-envelope phase difference mater. At relativistic laser intensities the target becomes a plasma layer generated, e.g. by the rising part of the incoming laser pulse. An approximate analytic solution has been given for the system of the coupled Maxwell-Lorentz equations describing the dynamics of the surface current (representing the plasma electrons) and the composite radiation field. With the help of these solutions the Fourier components of the reflected and transmitted radiation have been calculated. The nonlinearities stemming from the relativistic kinematics lead to the appearance of higher-order harmonics in the scattered

Generation of high harmonics and attosecond pulses with ultrashort ...

Indian Academy of Sciences (India)

2014-07-11

Jul 11, 2014 ... Two aspects of ultrashort pulse filaments are specifically discussed: (i) numerical simulation results on pulse self-compression by filamentation in a gas cell filled with noble gas. Measurements of high harmonics generated by the pulse extracted from the filament allows for the detection of intensity spikes ...

Asymmetry of light absorption upon propagation of focused femtosecond laser pulses with spatiotemporal coupling through glass materials

Science.gov (United States)

Zhukov, Vladimir P.; Bulgakova, Nadezhda M.

2017-05-01

Ultrashort laser pulses are usually described in terms of temporal and spatial dependences of their electric field, assuming that the spatial dependence is separable from time dependence. However, in most situations this assumption is incorrect as generation of ultrashort pulses and their manipulation lead to couplings between spatial and temporal coordinates resulting in various effects such as pulse front tilt and spatial chirp. One of the most intriguing spatiotemporal coupling effects is the so-called "lighthouse effect", the phase front rotation with the beam propagation distance [Akturk et al., Opt. Express 13, 8642 (2005)]. The interaction of spatiotemporally coupled laser pulses with transparent materials have interesting peculiarities, such as the effect of nonreciprocal writing, which can be used to facilitate microfabrication of photonic structures inside optical glasses. In this work, we make an attempt to numerically investigate the influence of the pulse front tilt and the lighthouse effect on the absorption of laser energy inside fused silica glass. The model, which is based on nonlinear Maxwell's equations supplemented by the hydrodynamic equations for free electron plasma, is applied. As three-dimensional solution of such a problem would require huge computational resources, a simplified two-dimensional model has been proposed. It has enabled to gain a qualitative insight into the features of propagation of ultrashort laser pulses with the tilted front in the regimes of volumetric laser modification of transparent materials, including directional asymmetry upon direct laser writing in glass materials.

Superintense fields from multiple ultrashort laser pulses retroreflected in circular geometry

Science.gov (United States)

Ooi, C. H. Raymond

2010-02-01

Laser field with superintensity beyond 1029 W/cm2 can be generated by coherent superposition of multiple 100 fs laser pulses in circular geometry setup upon retroreflection by a ring mirror. We have found the criteria for attaining such intensities using broadband ring mirror within the practical damage threshold and paraxial focusing regime. Simple expressions for the intensity enhancement factor are obtained, providing insight for achieving unlimited laser intensity. Higher intensities can be achieved by using few-cycle laser pulses.

Prepulse effect on intense femtosecond laser pulse propagation in gas

International Nuclear Information System (INIS)

Giulietti, Antonio; Tomassini, Paolo; Galimberti, Marco; Giulietti, Danilo; Gizzi, Leonida A.; Koester, Petra; Labate, Luca; Ceccotti, Tiberio; D'Oliveira, Pascal; Auguste, Thierry; Monot, Pascal; Martin, Philippe

2006-01-01

The propagation of an ultrashort laser pulse can be affected by the light reaching the medium before the pulse. This can cause a serious drawback to possible applications. The propagation in He of an intense 60-fs pulse delivered by a Ti:sapphire laser in the chirped pulse amplification (CPA) mode has been investigated in conditions of interest for laser-plasma acceleration of electrons. The effects of both nanosecond amplified spontaneous emission and picosecond pedestals have been clearly identified. There is evidence that such effects are basically of refractive nature and that they are not detrimental for the propagation of a CPA pulse focused to moderately relativistic intensity. The observations are fully consistent with numerical simulations and can contribute to the search of a stable regime for laser acceleration

New techniques of time-resolved infrared and Raman spectroscopy using ultrashort laser pulses

International Nuclear Information System (INIS)

Laubereau, A.

1986-01-01

Considerable progress has been made in recent years in the field of spectroscopic applications of ultrashort laser pulses. This paper examines two approaches toward studying ultrafast relaxation processes in condensed matter: an IR technique which complements coherent Raman scattering; and a Fourier Raman method with high frequency resolution. The time domain IR spectroscopy technique has been applied to various vibration-rotation transitions of pure HCl gas and in mixtures with Ar buffer gas. The advantage of the time domain measurements instead of frequency spectroscopy is readily visualized when one recalls that a frequency resolution of 10 -3 cm -1 corresponds to time observations over 10 -8 , which are readily feasible. As a first demonstration of the FT-Raman technique the author presents experimental data on the Q-branch of the v 1 -vibrational mode of methane. An example for the experimental data obtained approximately 2 mm behind the nozzle is presented; the coherent anti-Stokes Raman signal is plotted versus delay time. A complicated beating structure and the decay of the signal envelope are readily seen. The desired spectroscopic information is obtained by numerical Fourier transformation of the experimental points presented

K-shell spectra from hot dense aluminum layers buried in carbon and heated by ultrashort laser pulses

International Nuclear Information System (INIS)

Eidmann, K.; Andiel, U.; Pisani, F.; Hakel, P.; Mancini, R.C.; Junkel-Vives, G.C.; Abdallah, J.; Witte, K.

2003-01-01

Ultrashort laser pulses allow for the generation of hot plasmas near solid state densities. For this purpose a Ti:Sapphire laser was used, which delivers after frequency doubling, pulses of high contrast with an energy of about 60 mJ and a duration of 150 fs at 395 nm. The typical intensity on the target was a few 10 17 W/cm 2 . To achieve a high degree of uniformity we used targets consisting of a 25 nm thin Al tracer layer buried at different depths up to 400 nm in solid carbon. Time-integrated Al K-shell spectra are presented. Characteristic features of the spectra are significant high-order satellite line emission, strong line broadening and a center-of-mass line shift to the red, which was observed in transitions from principal quantum number n=2 or 3 to 1. Accurate measurement of the shift was made possible by using the cold Si K α line as an absolute wavelength calibration. In addition to time-integrated measurements, we used an ultrafast X-ray streak camera to obtain time and spectrally resolved spectra. Typical durations of the Ly α and He α lines are in the range 2-4 ps. The experimental results are compared with a time-dependent model, which combines hydrodynamic simulations, time-dependent atomic kinetics, detailed spectral line shapes including line shifts, and radiation transport

Double ionization of molecule H2 in intense ultrashort laser fields

International Nuclear Information System (INIS)

Le, Thu-Thuy; Nguyen, Ngoc-Ty

2015-01-01

By solving numerically the time-dependent Schrödinger equation (TDSE), we have calculated the double ionization probability when a vibrating hydrogen molecule interacts with intense ultrashort laser pulses. The results show that in the case of vibrating nuclei the double ionization probability is higher than that of the fixed nuclei. Additionally, the double ionization probability is larger if the molecule is vibrating in a higher level. This is due to the decreasing of ionization potential when the inter-nuclei separation increases. (paper)

Theoretical models for ultrashort electromagnetic pulse propagation in nonlinear metamaterials

International Nuclear Information System (INIS)

Wen, Shuangchun; Xiang, Yuanjiang; Dai, Xiaoyu; Tang, Zhixiang; Su, Wenhua; Fan, Dianyuan

2007-01-01

A metamaterial (MM) differs from an ordinary optical material mainly in that it has a dispersive magnetic permeability and offers greatly enhanced design freedom to alter the linear and nonlinear properties. This makes it possible for us to control the propagation of ultrashort electromagnetic pulses at will. Here we report on generic features of ultrashort electromagnetic pulse propagation and demonstrate the controllability of both the linear and nonlinear parameters of models for pulse propagation in MMs. First, we derive a generalized system of coupled three-dimensional nonlinear Schroedinger equations (NLSEs) suitable for few-cycle pulse propagation in a MM with both nonlinear electric polarization and nonlinear magnetization. The coupled equations recover previous models for pulse propagation in both ordinary material and a MM under the same conditions. Second, by using the coupled NLSEs in the Drude dispersive model as an example, we identify the respective roles of the dispersive electric permittivity and magnetic permeability in ultrashort pulse propagation and disclose some additional features of pulse propagation in MMs. It is shown that, for linear propagation, the sign and magnitude of space-time focusing can be controlled through adjusting the linear dispersive permittivity and permeability. For nonlinear propagation, the linear dispersive permittivity and permeability are incorporated into the nonlinear magnetization and nonlinear polarization, respectively, resulting in controllable magnetic and electric self-steepening effects and higher-order dispersively nonlinear terms in the propagation models

Ultra-short pulse, ultra-high intensity laser improvement techniques for laser-driven quantum beam science

International Nuclear Information System (INIS)

Kiriyama, Hiromitsu; Kando, Masaki

2014-01-01

Recent development activities of the Quantum Beam Research Team in JAEA are reported. The downsized, petawatt and femtosecond pulse laser is described at first. The process of the system development and utilization effort of so-called J-KAREN is explained with its time and space control system. For high contrast, OPCPA (Optical Parametric Chirped Pulse Amplification) preamplifier is adopted by using the titanium-sapphire laser system in which only the seed light pulses can be amplified. In addition, high contrast is obtained by adopting the high energy seed light to the amplifier. The system configuration of J-KAREN laser is illustrated. Typical spectra with and without OPCPA, as well as the spectra with OPCPA adjustment and without one are shown. The result of the recompressed pulses is shown in which the pulse width of 29.5 femtoseconds is close to the theoretical limit. Considering the throughput of the pulse compressor is 64 percent it is possible to generate high power laser beam of about 600 terawatts. In the supplementary budget of 2012, it has been approved to cope with the aging or obsoleteness of the system and at the same time to further sophisticate the laser using system. The upgraded laser system is named as J-KAREN-P in which the repetition rate is improved and another booster amplifier is added to increase the power. The system configuration of J-KAREN-P after the upgrading is illustrated. (S. Funahashi)

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.

Picosecond laser pulse-driven crystallization behavior of SiSb phase change memory thin films

International Nuclear Information System (INIS)

Huang Huan; Li Simian; Zhai Fengxiao; Wang Yang; Lai Tianshu; Wu Yiqun; Gan Fuxi

2011-01-01

Highlights: → We reported crystallization dynamics of a novel SiSb phase change material. → We measured optical constants of as-deposited and irradiated SiSb areas. → Optical properties of as-deposited and irradiated SiSb thin film were compared. → Crystallization of irradiated SiSb was confirmed by using AFM and micro-Raman spectra. → The heat conduction effect of lower metal layer of multi-layer films was studied. - Abstract: Transient phase change crystallization process of SiSb phase change thin films under the irradiation of picosecond (ps) laser pulse was studied using time-resolved reflectivity measurements. The ps laser pulse-crystallized domains were characterized by atomic force microscope, Raman spectra and ellipsometrical spectra measurements. A reflectivity contrast of about 15% can be achieved by ps laser pulse-induced crystallization. A minimum crystallization time of 11 ns was achieved by a low-fluence single ps laser pulse after pre-irradiation. SiSb was shown to be very promising for fast phase change memory applications.

Photoelectron emission from metal surfaces by ultrashort laser pulses

International Nuclear Information System (INIS)

Faraggi, M. N.; Gravielle, M. S.; Silkin, V. M.

2006-01-01

Electron emission from metal surfaces produced by short laser pulses is studied within the framework of the distorted-wave formulation. The proposed approach, named surface-Volkov (SV) approximation, makes use of the band-structure based (BSB) model and the Volkov phase to describe the interaction of the emitted electron with the surface and the external electric field, respectively. The BSB model provides a realistic representation of the surface, based on a model potential that includes the main features of the surface band structure. The SV method is applied to evaluate the photoelectron emission from the valence band of Al(111). Angular and energy distributions are investigated for different parameters of the laser pulse, keeping in all cases the carrier frequency larger than the plasmon one

Magnetic Field Effect on Ultrashort Two-dimensional Optical Pulse Propagation in Silicon Nanotubes

Science.gov (United States)

Konobeeva, N. N.; Evdokimov, R. A.; Belonenko, M. B.

2018-05-01

The paper deals with the magnetic field effect which provides a stable propagation of ultrashort pulses in silicon nanotubes from the viewpoint of their waveform. The equation is derived for the electromagnetic field observed in silicon nanotubes with a glance to the magnetic field for two-dimensional optical pulses. The analysis is given to the dependence between the waveform of ultrashort optical pulses and the magnetic flux passing through the cross-sectional area of the nanotube.

Nonlinear shaping of a two-dimensional ultrashort ionizing pulse

International Nuclear Information System (INIS)

Sergeev, A.; Vanin, E.; Stenflo, L.; Anderson, D.; Lisak, M.; Quiroga-Teixeiro, M.L.

1992-01-01

A theoretical description of ultrashort ionizing wave pulses is presented by means of two different models where the ionization rate increases or decreases, respectively, as a function of the electric field amplitude. We show that the pulse evolves either into a horse-shoe or a horn-type structure in the time-space domain. In some parameter regions the intensity of the pulse can also increase. (au)

Long Wavelength Electromagnetic Light Bullets Generated by a 10.6 micron CO2 Ultrashort Pulsed Source

Science.gov (United States)

2016-11-29

AFRL-AFOSR-VA-TR-2016-0365 Long Wavelength Electromagnetic Light Bullets Generated by a 10.6 micron CO2 Ultrashort Pulsed Source Jerome Moloney...SUBTITLE "Long Wavelength Electromagnetic Light Bullets Generated by a 10.6 micron CO2 Ultrashort Pulsed Source 5a. CONTRACT NUMBER FA9550-15-1-0272 5b...Wavelength Electromagnetic Light Bullets Generated by a 10 µm CO2 Ultrashort Pulsed Source Grant/Contract Number AFOSR assigned control number. It must

Modeling ultrashort electromagnetic pulses with a generalized Kadomtsev-Petviashvili equation

Science.gov (United States)

Hofstrand, A.; Moloney, J. V.

2018-03-01

In this paper we derive a properly scaled model for the nonlinear propagation of intense, ultrashort, mid-infrared electromagnetic pulses (10-100 femtoseconds) through an arbitrary dispersive medium. The derivation results in a generalized Kadomtsev-Petviashvili (gKP) equation. In contrast to envelope-based models such as the Nonlinear Schrödinger (NLS) equation, the gKP equation describes the dynamics of the field's actual carrier wave. It is important to resolve these dynamics when modeling ultrashort pulses. We proceed by giving an original proof of sufficient conditions on the initial pulse for a singularity to form in the field after a finite propagation distance. The model is then numerically simulated in 2D using a spectral-solver with initial data and physical parameters highlighting our theoretical results.

Ultrashort pulsed laser ablation for decollation of solid state lithium-ion batteries

Science.gov (United States)

Hördemann, C.; Anand, H.; Gillner, A.

2017-08-01

Rechargeable lithium-ion batteries with liquid electrolytes are the main energy source for many electronic devices that we use in our everyday lives. However, one of the main drawbacks of this energy storage technology is the use of liquid electrolyte, which can be hazardous to the user as well as the environment. Moreover, lithium-ion batteries are limited in voltage, energy density and operating temperature range. One of the most novel and promising battery technologies available to overcome the above-mentioned drawbacks is the Solid-State Lithium-Ion Battery (SSLB). This battery type can be produced without limitations to the geometry and is also bendable, which is not possible with conventional batteries1 . Additionally, SSLBs are characterized by high volumetric and gravimetric energy density and are intrinsically safe since no liquid electrolyte is used2-4. Nevertheless, the manufacturing costs of these batteries are still high. The existing production-technologies are comparable to the processes used in the semiconductor industry and single cells are produced in batches with masked-deposition at low deposition rates. In order to decrease manufacturing costs and to move towards continuous production, Roll2Roll production methods are being proposed5, 6. These methods offer the possibility of producing large quantities of substrates with deposited SSLB-layers. From this coated substrate, single cells can be cut out. For the flexible decollation of SSLB-cells from the substrate, new manufacturing technologies have to be developed since blade-cutting, punching or conventional laser-cutting processes lead to short circuiting between the layers. Here, ultra-short pulsed laser ablation and cutting allows the flexible decollation of SSLBs. Through selective ablation of individual layers, an area for the cutting kerf is prepared to ensure a shortcut-free decollation.

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.

Ultra-short laser interactions with nanoparticles in different media: from electromagnetic to thermal and electrostatic effects

Science.gov (United States)

Itina, Tatiana E.

2017-02-01

Key issues of the controlled synthesis of nanoparticles and nanostructures, as well as laser-particle interactions are considered in the context of the latest applications appearing in many fields such as photonics, medicine, 3D printing, etc. The results of a multi-physics numerical study of laser interaction with nanoparticles will be presented in the presence of several environments. In particular, attention will be paid to the numerical study of laser interactions with heterogeneous materials (eg. colloidal liquids and/or nanoparticles in a dielectric medium) and the aggregation/sintering/fragmentation processes induced by ultra-short laser pulses.

Pulse-shaping strategies in short-pulse fiber amplifiers

Energy Technology Data Exchange (ETDEWEB)

Schimpf, Damian Nikolaus

2010-02-09

Ultrashort pulse lasers are an important tool in scientific and industrial applications. However, many applications are demanding higher average powers from these ultrashort pulse sources. This can be achieved by combining direct diode pumping with novel gain media designs. In particular, ultrashort pulse fiber lasers are now delivering average powers in the kW range. However, the design of fiber lasers, producing pulses with high peak-powers, is challenging due to the impact of nonlinear effects. To significantly reduce these detrimental effects in ultrashort pulse fiber amplifers, the combination of chirped pulse amplification (CPA) and large mode area fibers is employed. Using these methods, the pulse energy of fiber lasers has been steadily increasing for the past few years. Recently, a fiber-based CPA-system has been demonstrated which produces pulse energies of around 1 mJ. However, both the stretching and the enlargement of the mode area are limited, and therefore, the impact of nonlinearity is still noticed in systems employing such devices. The aim of this thesis is the analysis of CPA-systems operated beyond the conventional nonlinear limit, which corresponds to accumulated nonlinear phase-shifts around 1 rad. This includes a detailed discussion of the influence of the nonlinear effect self-phase modulation on the output pulse of CPA-systems. An analytical model is presented. Emphasis is placed on the design of novel concepts to control the impact of self-phase modulation. Pulse-shaping is regarded as a powerful tool to accomplish this goal. Novel methods to control the impact of SPM are experimentally demonstrated. The design of these concepts is based on the theoretical findings. Both amplitude- and phase-shaping are studied. Model-based phase-shaping is implemented in a state-of-the-art fiber CPA-system. The influence of the polarization state is also highlighted. Additionally, existing techniques and recent advances are put into context. (orig.)

Pulse-shaping strategies in short-pulse fiber amplifiers

International Nuclear Information System (INIS)

Schimpf, Damian Nikolaus

2010-01-01

Ultrashort pulse lasers are an important tool in scientific and industrial applications. However, many applications are demanding higher average powers from these ultrashort pulse sources. This can be achieved by combining direct diode pumping with novel gain media designs. In particular, ultrashort pulse fiber lasers are now delivering average powers in the kW range. However, the design of fiber lasers, producing pulses with high peak-powers, is challenging due to the impact of nonlinear effects. To significantly reduce these detrimental effects in ultrashort pulse fiber amplifers, the combination of chirped pulse amplification (CPA) and large mode area fibers is employed. Using these methods, the pulse energy of fiber lasers has been steadily increasing for the past few years. Recently, a fiber-based CPA-system has been demonstrated which produces pulse energies of around 1 mJ. However, both the stretching and the enlargement of the mode area are limited, and therefore, the impact of nonlinearity is still noticed in systems employing such devices. The aim of this thesis is the analysis of CPA-systems operated beyond the conventional nonlinear limit, which corresponds to accumulated nonlinear phase-shifts around 1 rad. This includes a detailed discussion of the influence of the nonlinear effect self-phase modulation on the output pulse of CPA-systems. An analytical model is presented. Emphasis is placed on the design of novel concepts to control the impact of self-phase modulation. Pulse-shaping is regarded as a powerful tool to accomplish this goal. Novel methods to control the impact of SPM are experimentally demonstrated. The design of these concepts is based on the theoretical findings. Both amplitude- and phase-shaping are studied. Model-based phase-shaping is implemented in a state-of-the-art fiber CPA-system. The influence of the polarization state is also highlighted. Additionally, existing techniques and recent advances are put into context. (orig.)

Two-temperature hydrodynamic expansion and coupling of strong elastic shock with supersonic melting front produced by ultrashort laser pulse

International Nuclear Information System (INIS)

Inogamov, Nail A; Khokhlov, Viktor A; Zhakhovsky, Vasily V; Khishchenko, Konstantin V; Demaske, Brian J; Oleynik, Ivan I

2014-01-01

Ultrafast processes, including nonmonotonic expansion of material into vacuum, supersonic melting and generation of super-elastic shock wave, in a surface layer of metal irradiated by an ultrashort laser pulse are discussed. In addition to the well-established two-temperature (2T) evolution of heated layer a new effect of electron pressure gradient on early stage of material expansion is studied. It is shown that the expanding material experiences an unexpected jump in flow velocity in a place where stress exceeds the effective tensile strength provided by used EoS of material. Another 2T effect is that supersonic propagation of homogeneous melting front results in distortion of spatial profile of ion temperature, which later imprints on ion pressure profile transforming in a super-elastic shock wave with time.

High-energy-throughput pulse compression by off-axis group-delay compensation in a laser-induced filament

International Nuclear Information System (INIS)

Voronin, A. A.; Alisauskas, S.; Muecke, O. D.; Pugzlys, A.; Baltuska, A.; Zheltikov, A. M.

2011-01-01

Off-axial beam dynamics of ultrashort laser pulses in a filament enable a radical energy-throughput improvement for filamentation-assisted pulse compression. We identify regimes where a weakly diverging wave, produced on the trailing edge of the pulse, catches up with a strongly diverging component, arising in the central part of the pulse, allowing sub-100-fs millijoule infrared laser pulses to be compressed to 20-25-fs pulse widths with energy throughputs in excess of 70%. Theoretical predictions have been verified by experimental results on filamentation-assisted compression of 70-fs, 1.5-μm laser pulses in high-pressure argon.

Inelastic processes in interaction of an atom with ultrashort pulse of an electromagnetic field

International Nuclear Information System (INIS)

Matveev, V.I.; Gusarevich, E.S.; Pashev, I.N.

2005-01-01

Electron transitions occurring when a heavy relativistic atom interacts with a spatially inhomogeneous ultrashort electromagnetic pulse are considered. Transition probabilities are expressed in terms of the known inelastic atomic form factors. By way of example, the inelastic processes accompanying the interaction of ultrashort pulses with hydrogen-like atoms are considered. The probabilities of ionization and production of a bound-free electron-positron pair on a bare nucleus, which are accompanied by the formation of a hydrogen-like atom in the final state and a positron in the continuum, are calculated. The developed technique makes it possible to take into exact account magnetic interaction besides spatial inhomogeneity of an ultrashort electromagnetic pulse [ru

Measurement of Ultra-Short Solitary Electromagnetic Pulses

Directory of Open Access Journals (Sweden)

Eva Gescheidtova

2004-01-01

Full Text Available In connection with the events of the last few years and with the increased number of terrorist activities, the problem of identification and measurement of electromagnetic weapons or other systems impact occurred. Among these are also microwave sources, which can reach extensive peak power of up to Pmax = 100 MW. Solitary, in some cases several times repeated, impulses lasting from tp E <1, 60>ns, cause the destruction of semiconductor junctions. These days we can find scarcely no human activity, where semiconductor structures are not used. The problem of security support of the air traffic, transportation, computer nets, banks, national strategic data canter’s, and other applications crops up. Several types of system protection from the ultra-short electromagnetic pulses present itself, passive and active protection. The analysis of the possible measuring methods, convenient for the identification and measurement of the ultra-short solitary electromagnetic pulses in presented in this paper; some of the methods were chosen and used for practical measurement. This work is part of Research object MSM262200022 "Research of microelectronic systems".

Simulation of condensed matter dynamics in strong femtosecond laser pulses

International Nuclear Information System (INIS)

Wachter, G.

2014-01-01

Ultrashort custom-tailored laser pulses can be employed to observe and control the motion of electrons in atoms and small molecules on the (sub-) femtosecond time scale. Very recently, efforts are underway to extend these concepts to solid matter. This monograph theoretically explores first applications of electron control by ultrashort laser pulses in three paradigmatic systems of solid-state density: a metal nano-structure (nanometric metal tip), a bulk dielectric (quartz glass), and the buckminsterfullerene molecule (C60) as arguably the smallest possible nano-particle. The electron motion is resolved on the atomic length and time scale by ab-initio simulations based on time-dependent density functional theory. Our quantum simulations are complemented by classical and semi-classical models elucidating the underlying mechanisms. We compare our results to experiments where already available and find good agreement. With increasing laser intensity, we find a transition from vertical photoexcitation to tunneling-like excitation. For nanostructures, that leads to temporally confined electron photoemission and thereby to quantum interferences in the energy spectra of emitted electrons. Similarly, tunneling can be induced between neighboring atoms inside an insulator. This provides a mechanism for ultrafast light-field controlled currents and modification of the optical properties of the solid, promising to eventually realize light-field electronic devices operating on the femtosecond time scale and nanometer length scale. Electron-electron interaction leads to near field enhancement and spatial localization of the non-linear response and is investigated both classically by solving the Maxwell equations near a nanostructure as well as quantum mechanically for the fullerene molecule. For the latter, we discuss scrutiny of the molecular near-field by the attosecond streaking technique. Our results demonstrate that ultrashort laser pulses can be employed to steer the

Controlling the porosity of collagen, gelatin and elastin biomaterials by ultrashort laser pulses

International Nuclear Information System (INIS)

Daskalova, A.; Nathala, Chandra S.R.; Bliznakova, I.; Stoyanova, E.; Zhelyazkova, A.; Ganz, T.; Lueftenegger, S.; Husinsky, W.

2014-01-01

We report on the structural investigation of self-organized micropores generated in thin gelatin, collagen, and collagen–elastin films after single and multishot irradiation with pulse durations ranging from 30–100 fs at 800 nm. We systematically studied the effect of laser parameters: laser energy, number of pulses, and pulse duration on the development of the micropores. This work showed that applying laser pulses at different rates significantly modified the thin film surface. The results clearly revealed that femtosecond laser treatment of thin films of biomaterials: gelatin, collagen and collagen–elastin, results in creation of micro/nanopores with different size of cavity formations. Experimentally, it is demonstrated that it is possible to influence the dimensions of the pore sizes, ranging from 100 nm to 2 μm by tuning the laser parameters. We are currently further exploring the possibility of structuring these biomaterials by applying a time delay between separate pulses. First results from cell culture experiments on laser created surface foam of collagen–elastin were successfully obtained, showing the potential of the method to cultivate cells on superficial porous substrates and the preferable selectivity of the cells to proliferate on the laser modified parts of the biopolymer substrate.

Controlling the porosity of collagen, gelatin and elastin biomaterials by ultrashort laser pulses

Energy Technology Data Exchange (ETDEWEB)

Daskalova, A., E-mail: a_daskalova@code.bg [Institute of Electronics, Bulgarian Academy of Sciences, 72, Tsarigradsko Chaussee blvd., 1784 Sofia (Bulgaria); Nathala, Chandra S.R. [IAP, Vienna University of Technology, Wiedner Hauptstrasse 8-10, 1040 Vienna (Austria); Femtolasers Productions GmbH, Fernkorngasse10, 1100 Vienna (Austria); Bliznakova, I. [Institute of Electronics, Bulgarian Academy of Sciences, 72, Tsarigradsko Chaussee blvd., 1784 Sofia (Bulgaria); Stoyanova, E. [IBIR, Department of Molecular Immunology, Bulgarian Academy of Sciences, 73, Tzarigradsko Chaussee blvd., 1113 Sofia (Bulgaria); Zhelyazkova, A. [Institute of Electronics, Bulgarian Academy of Sciences, 72, Tsarigradsko Chaussee blvd., 1784 Sofia (Bulgaria); Ganz, T. [Femtolasers Productions GmbH, Fernkorngasse10, 1100 Vienna (Austria); Lueftenegger, S.; Husinsky, W. [IAP, Vienna University of Technology, Wiedner Hauptstrasse 8-10, 1040 Vienna (Austria)

2014-02-15

We report on the structural investigation of self-organized micropores generated in thin gelatin, collagen, and collagen–elastin films after single and multishot irradiation with pulse durations ranging from 30–100 fs at 800 nm. We systematically studied the effect of laser parameters: laser energy, number of pulses, and pulse duration on the development of the micropores. This work showed that applying laser pulses at different rates significantly modified the thin film surface. The results clearly revealed that femtosecond laser treatment of thin films of biomaterials: gelatin, collagen and collagen–elastin, results in creation of micro/nanopores with different size of cavity formations. Experimentally, it is demonstrated that it is possible to influence the dimensions of the pore sizes, ranging from 100 nm to 2 μm by tuning the laser parameters. We are currently further exploring the possibility of structuring these biomaterials by applying a time delay between separate pulses. First results from cell culture experiments on laser created surface foam of collagen–elastin were successfully obtained, showing the potential of the method to cultivate cells on superficial porous substrates and the preferable selectivity of the cells to proliferate on the laser modified parts of the biopolymer substrate.

Fibre amplifier based on an ytterbium-doped active tapered fibre for the generation of megawatt peak power ultrashort optical pulses

Energy Technology Data Exchange (ETDEWEB)

Koptev, M Yu; Anashkina, E A; Lipatov, D S; Andrianov, A V; Muravyev, S V; Kim, A V [Lobachevsky State University of Nizhny Novgorod, Nizhny Novgorod (Russian Federation); Bobkov, K K; Likhachev, M E; Levchenko, A E; Aleshkina, S S; Semjonov, S L; Denisov, A N; Bubnov, M M [Fiber Optics Research Center, Russian Academy of Sciences, Moscow (Russian Federation); Laptev, A Yu; Gur' yanov, A N [G.G.Devyatykh Institute of Chemistry of High-Purity Substances, Russian Academy of Sciences, Nizhnii Novgorod (Russian Federation)

2015-05-31

We report a new ytterbium-doped active tapered fibre used in the output amplifier stage of a fibre laser system for the generation of megawatt peak power ultrashort pulses in the microjoule energy range. The tapered fibre is single-mode at its input end (core and cladding diameters of 10 and 80 μm) and multimode at its output end (diameters of 45 and 430 μm), but ultrashort pulses are amplified in a quasi-single-mode regime. Using a hybrid Er/Yb fibre system comprising an erbium master oscillator and amplifier at a wavelength near 1.5 μm, a nonlinear wavelength converter to the 1 μm range and a three-stage ytterbium-doped fibre amplifier, we obtained pulses of 1 μJ energy and 7 ps duration, which were then compressed by a grating-pair dispersion compressor with 60% efficiency to a 130 fs duration, approaching the transform-limited pulse duration. The present experimental data agree well with numerical simulation results for pulse amplification in the threestage amplifier. (extreme light fields and their applications)

Self-cleaning effect in high quality percussion ablating of cooling hole by picosecond ultra-short pulse laser

Science.gov (United States)

Zhao, Wanqin; Yu, Zhishui

2018-06-01

Comparing with the trepanning technology, cooling hole could be processed based on the percussion drilling with higher processing efficiency. However, it is widely believed that the ablating precision of hole is lower for percussion drilling than for trepanning, wherein, the melting spatter materials around the hole surface and the recast layer inside the hole are the two main issues for reducing the ablating precision of hole, especially for the recast layer, it can't be eliminated completely even through the trepanning technology. In this paper, the self-cleaning effect which is a particular property just for percussion ablating of holes has been presented in detail. In addition, the reasons inducing the self-cleaning effect have been discussed. At last, based on the self-cleaning effect of percussion drilling, high quality cooling hole without the melting spatter materials around the hole surface and recast layer inside the hole could be ablated in nickel-based superalloy by picosecond ultra-short pulse laser.

Scattering of ultrashort electromagnetic pulses on metal clusters

International Nuclear Information System (INIS)

Astapenko, V. A.; Sakhno, S. V.

2016-01-01

We have calculated and analyzed the probability of ultrashort electromagnetic pulse (USP) scattering on small metal clusters in the frequency range of plasmon resonances during the field action. The main attention is devoted to dependence of the probability of scattering on the pulse duration for various detunings of the USP carrier frequency from the plasmon resonance frequency. Peculiarities of the USP scattering from plasmon resonances with various figures of merit are revealed.

Scattering of ultrashort electromagnetic pulses on metal clusters

Energy Technology Data Exchange (ETDEWEB)

Astapenko, V. A., E-mail: astval@mail.ru; Sakhno, S. V. [Moscow Institute of Physics and Technology (State University) (Russian Federation)

2016-12-15

We have calculated and analyzed the probability of ultrashort electromagnetic pulse (USP) scattering on small metal clusters in the frequency range of plasmon resonances during the field action. The main attention is devoted to dependence of the probability of scattering on the pulse duration for various detunings of the USP carrier frequency from the plasmon resonance frequency. Peculiarities of the USP scattering from plasmon resonances with various figures of merit are revealed.

Ultrashort pulse laser machining of metals and alloys

Science.gov (United States)

Perry, Michael D.; Stuart, Brent C.

2003-09-16

The invention consists of a method for high precision machining (cutting, drilling, sculpting) of metals and alloys. By using pulses of a duration in the range of 10 femtoseconds to 100 picoseconds, extremely precise machining can be achieved with essentially no heat or shock affected zone. Because the pulses are so short, there is negligible thermal conduction beyond the region removed resulting in negligible thermal stress or shock to the material beyond approximately 0.1-1 micron (dependent upon the particular material) from the laser machined surface. Due to the short duration, the high intensity (>10.sup.12 W/cm.sup.2) associated with the interaction converts the material directly from the solid-state into an ionized plasma. Hydrodynamic expansion of the plasma eliminates the need for any ancillary techniques to remove material and produces extremely high quality machined surfaces with negligible redeposition either within the kerf or on the surface. Since there is negligible heating beyond the depth of material removed, the composition of the remaining material is unaffected by the laser machining process. This enables high precision machining of alloys and even pure metals with no change in grain structure.

Supercomputations and big-data analysis in strong-field ultrafast optical physics: filamentation of high-peak-power ultrashort laser pulses

Science.gov (United States)

Voronin, A. A.; Panchenko, V. Ya; Zheltikov, A. M.

2016-06-01

High-intensity ultrashort laser pulses propagating in gas media or in condensed matter undergo complex nonlinear spatiotemporal evolution where temporal transformations of optical field waveforms are strongly coupled to an intricate beam dynamics and ultrafast field-induced ionization processes. At the level of laser peak powers orders of magnitude above the critical power of self-focusing, the beam exhibits modulation instabilities, producing random field hot spots and breaking up into multiple noise-seeded filaments. This problem is described by a (3  +  1)-dimensional nonlinear field evolution equation, which needs to be solved jointly with the equation for ultrafast ionization of a medium. Analysis of this problem, which is equivalent to solving a billion-dimensional evolution problem, is only possible by means of supercomputer simulations augmented with coordinated big-data processing of large volumes of information acquired through theory-guiding experiments and supercomputations. Here, we review the main challenges of supercomputations and big-data processing encountered in strong-field ultrafast optical physics and discuss strategies to confront these challenges.

Scattering of an ultrashort electromagnetic pulse in a plasma

International Nuclear Information System (INIS)

Astapenko, V. A.

2011-01-01

An analytic approach is developed to describing how ultrashort electromagnetic pulses with a duration of one period or less at the carrier frequency are scattered in a plasma. Formulas are derived to calculate and analyze the angular and spectral probabilities of radiation scattering via two possible mechanisms-Compton and transition radiation channels-throughout the entire pulse. Numerical simulations were carried out for a Gaussian pulse. The effect of the phase of the carrier frequency relative to the pulse envelope on the scattering parameters is investigated.

Inelastic Processes in the Interaction of an Atom with an Ultrashort Electromagnetic Pulse

International Nuclear Information System (INIS)

Matveev, V.I.; Gusarevich, E.S.; Pashev, I.N.

2005-01-01

Electron transitions occurring during the interaction of a heavy relativistic atom with a spatially inhomogeneous ultrashort electromagnetic pulse are considered by solving the Dirac equation. The corresponding transition probabilities are expressed in terms of known inelastic atomic form factors, which are widely used in the theory of relativistic collisions between charged particles and atoms. By way of example, the inelastic processes accompanying the interaction of ultrashort pulses with hydrogen-like atoms are considered. The probabilities of ionization and production of a bound-free electron-positron pair on a bare nucleus, which are accompanied by the formation of a hydrogen-like atom in the final state and a positron in the continuum, are calculated. The developed technique makes it possible to take into account exactly not only the spatial inhomogeneity of an ultrashort electromagnetic pulse, but also the magnetic interaction

Zero photon dissociation of CS2+ in intense ultrashort laser pulses

Science.gov (United States)

Severt, Travis; Betsch, K. J.; Zohrabi, M.; Ablikim, U.; Jochim, Bethany; Carnes, K. D.; Esry, B. D.; Ben-Itzhak, I.

2013-05-01

We measured the dissociation of a CS2+ molecular ion beam in intense laser pulses ( C+ + S+. We speculate that a pump-dump process occurs whereby the vibrational wavepacket in the electronic ground state of CS2+ is pumped into the electronic first excited state's continuum by a single photon during the laser pulse. Once this continuum vibrational wavepacket passes the potential barrier in the ground electronic potential, the emission of a second photon is stimulated by the same laser pulse, most likely when the wavepacket moves through the internuclear distance where the two electronic states are in resonance with the driving field. A comparison is made to ZPD and ATD in the isovalent CO2+ species. Curiously, ATD is the favored mechanism in CO2+. The underlying molecular structure and dynamics determining this preference will be discussed. Supported by Chemical Sciences, Geosciences, and Biosciences Division, Office of Basic Energy Sciences, Office of Science, U.S. Department of Energy.

Propagation and spatiotemporal coupling characteristics of ultra-short Gaussian vortex pulse

Science.gov (United States)

Nie, Jianye; Liu, Guodong; Zhang, Rongzhu

2018-05-01

Based on Collins diffraction integral formula, the propagation equation of ultra-short Gaussian vortex pulse beam has been derived. Using the equation, the intensity distribution variations of vortex pulse in the propagation process are calculated. Specially, the spatiotemporal coupling characteristics of ultra-short vortex beams are discussed in detail. The results show that some key parameters, such as transverse distance, transmission distance, pulse width and topological charge number will influence the spatiotemporal coupling characteristics significantly. With the increasing of transverse distance, the waveforms of the pulses distort obviously. And when transmission distance is far than 50 mm, the distribution curve of transverse intensity gradually changes into a Gaussian type. In addition, initial pulse width will affect the distribution of light field, however, when initial pulse width is larger than 3 fs, the spatiotemporal coupling effect will be insignificant. Topological charge number does not affect the time delay characteristics, since with the increasing of topological charge number, the waveform of the pulse distorts gradually but the time delay does not occur.

Retinal response of Macaca mulatta to picosecond laser pulses of varying energy and spot size.

Science.gov (United States)

Roach, William P; Cain, Clarence P; Narayan, Drew G; Noojin, Gary D; Boppart, Stephen A; Birngruber, Reginald; Fujimoto, James G; Toth, Cynthia A

2004-01-01

We investigate the relationship between the laser beam at the retina (spot size) and the extent of retinal injury from single ultrashort laser pulses. From previous studies it is believed that the retinal effect of single 3-ps laser pulses should vary in extent and location, depending on the occurrence of laser-induced breakdown (LIB) at the site of laser delivery. Single 3-ps pulses of 580-nm laser energy are delivered over a range of spot sizes to the retina of Macaca mulatta. The retinal response is captured sequentially with optical coherence tomography (OCT). The in vivo OCT images and the extent of pathology on final microscopic sections of the laser site are compared. With delivery of a laser pulse with peak irradiance greater than that required for LIB, OCT and light micrographs demonstrate inner retinal injury with many intraretinal and/or vitreous hemorrhages. In contrast, broad outer retinal injury with minimal to no choriocapillaris effect is seen after delivery of laser pulses to a larger retinal area (60 to 300 microm diam) when peak irradiance is less than that required for LIB. The broader lesions extend into the inner retina when higher energy delivery produces intraretinal injury. Microscopic examination of stained fixed tissues provide better resolution of retinal morphology than OCT. OCT provides less resolution but could be guided over an in vivo, visible retinal lesion for repeated sampling over time during the evolution of the lesion formation. For 3-ps visible wavelength laser pulses, varying the spot size and laser energy directly affects the extent of retinal injury. This again is believed to be partly due to the onset of LIB, as seen in previous studies. Spot-size dependence should be considered when comparing studies of retinal effects or when pursuing a specific retinal effect from ultrashort laser pulses. Copyright 2004 Society of Photo-Optical Instrumentation Engineers.

Self-guiding of high-intensity laser pulses for laser wake field acceleration

International Nuclear Information System (INIS)

Umstader, D.; Liu, X.

1992-01-01

A means of self-guiding an ultrashort and high-intensity laser pulse is demonstrated both experimentally and numerically. Its relevance to the laser wake field accelerator concept is discussed. Self-focusing and multiple foci formation are observed when a high peak power (P>100 GW), 1 μm, subpicosecond laser is focused onto various gases (air or hydrogen). It appears to result from the combined effects of self-focusing by the gas, and de-focusing both by diffraction and the plasma formed in the central high-intensity region. Quasi-stationary computer simulations show the same multiple foci behavior as the experiments. The results suggest much larger nonlinear electronic susceptibilities of a gas near or undergoing ionization in the high field of the laser pulse. Although self-guiding of a laser beam by this mechanism appears to significantly extend its high-intensity focal region, small-scale self-focusing due to beam non-uniformity is currently a limitation

Attosecond time-energy structure of X-ray free-electron laser pulses

Science.gov (United States)

Hartmann, N.; Hartmann, G.; Heider, R.; Wagner, M. S.; Ilchen, M.; Buck, J.; Lindahl, A. O.; Benko, C.; Grünert, J.; Krzywinski, J.; Liu, J.; Lutman, A. A.; Marinelli, A.; Maxwell, T.; Miahnahri, A. A.; Moeller, S. P.; Planas, M.; Robinson, J.; Kazansky, A. K.; Kabachnik, N. M.; Viefhaus, J.; Feurer, T.; Kienberger, R.; Coffee, R. N.; Helml, W.

2018-04-01

The time-energy information of ultrashort X-ray free-electron laser pulses generated by the Linac Coherent Light Source is measured with attosecond resolution via angular streaking of neon 1s photoelectrons. The X-ray pulses promote electrons from the neon core level into an ionization continuum, where they are dressed with the electric field of a circularly polarized infrared laser. This induces characteristic modulations of the resulting photoelectron energy and angular distribution. From these modulations we recover the single-shot attosecond intensity structure and chirp of arbitrary X-ray pulses based on self-amplified spontaneous emission, which have eluded direct measurement so far. We characterize individual attosecond pulses, including their instantaneous frequency, and identify double pulses with well-defined delays and spectral properties, thus paving the way for X-ray pump/X-ray probe attosecond free-electron laser science.

Comparative study of the dissociative ionization of 1,1,1-trichloroethane using nanosecond and femtosecond laser pulses

CSIR Research Space (South Africa)

Du Plessis, A

2010-03-01

Full Text Available , but different fragmentation patterns. A general trend is that when using femtosecond laser pulses for ionization, the parent molecular ion is observed but not for nanosecond laser ionization. There is also a fundamental interest in laser...-molecule interactions at the high intensities available from femtosecond lasers [12,13]. These papers describe the multiphoton ionization mechanisms termed ladder climbing and ladder switching, which explain the presence of parent molecular ion in ultrashort pulse...

Laser and Plasma Parameters for Laser Pulse Amplification by Stimulated Brillouin Backscattering in the Strong Coupling Regime

Science.gov (United States)

Gangolf, Thomas; Blecher, Marius; Bolanos, Simon; Lancia, Livia; Marques, Jean-Raphael; Cerchez, Mirela; Prasad, Rajendra; Aurand, Bastian; Loiseau, Pascal; Fuchs, Julien; Willi, Oswald

2017-10-01

In the ongoing quest for novel techniques to obtain ever higher laser powers, plasma amplification has drawn much attention, benefiting from the fact that a plasma can sustain much higher energy densities than a solid state amplifier. As a plasma process, Stimulated Brillouin Backscattering in the strong coupling regime (sc-SBS) can be used to transfer energy from one laser pulse (pump) to another (seed), by a nonlinear ion oscillation forced by the pump laser. Here, we report on experimental results on amplification by sc-SBS using the ARCTURUS Ti:Sapphire multi-beam laser system at the University of Duesseldorf, Germany. Counter-propagating in a supersonic Hydrogen gas jet target, an ultrashort seed pulse with a pulse duration between 30 and 160 fs and an energy between 1 and 12 mJ was amplified by a high-energy pump pulse (1.7 ps, 700 mJ). For some of the measurements, the gas was pre-ionized with a separate laser pulse (780 fs, 460 mJ). Preliminary analysis shows that the amplification was larger for the longer seed pulses, consistent with theoretical predictions.

Controlled modification of biomolecules by ultrashort laser pulses in polar liquids

DEFF Research Database (Denmark)

Gruzdev, Vitaly; Korkin, Dmitry; Mooney, Brian P.

2017-01-01

Targeted chemical modification of peptides and proteins by laser pulses in a biologically relevant environment, i.e. aqueous solvent at room temperature, allows for accurate control of biological processes. However, the traditional laser methods of control of chemical reactions are applicable onl...

Analytic description of Raman-induced frequency shift in the case of non-soliton ultrashort pulses

Energy Technology Data Exchange (ETDEWEB)

Bugay, Aleksandr N., E-mail: bugay_aleksandr@mail.ru [Joint Institute for Nuclear Research, Joliot-Curie 6, 141980, Dubna, Moscow Region (Russian Federation); Khalyapin, Vyacheslav A., E-mail: slavasxi@gmail.com [Immanuel Kant Baltic Federal University, Kaliningrad, 236041 (Russian Federation); Kaliningrad State Technical University, Kaliningrad, 236000 (Russian Federation)

2017-01-30

Raman-induced frequency shift of ultrashort pulses have been studied extensively for the soliton propagation regime. Here we derive explicit analytic expressions for the evolution of Raman-induced frequency shift in much less studied case of non-soliton ultrashort pulses. Pulse spectra may belong to any region of group velocity dispersion including zero group dispersion point. The analysis is based on the moment method. Obtained expressions fit well to the numerical solution of the nonlinear wave equation. - Highlights: • Explicit analytic formulas for the evolution of Raman-induced frequency shift are derived in the case of non-soliton pulses. • Dynamics of non-soliton ultrashort pulses in the cases of positive and zero group dispersion is considered. • The deceleration and the saturation of Raman-induced frequency shift are analyzed. • The calculation relies on the moment method and fit well to the numerical solution of the nonlinear wave equation.

Analytic description of Raman-induced frequency shift in the case of non-soliton ultrashort pulses

International Nuclear Information System (INIS)

Bugay, Aleksandr N.; Khalyapin, Vyacheslav A.

2017-01-01

Raman-induced frequency shift of ultrashort pulses have been studied extensively for the soliton propagation regime. Here we derive explicit analytic expressions for the evolution of Raman-induced frequency shift in much less studied case of non-soliton ultrashort pulses. Pulse spectra may belong to any region of group velocity dispersion including zero group dispersion point. The analysis is based on the moment method. Obtained expressions fit well to the numerical solution of the nonlinear wave equation. - Highlights: • Explicit analytic formulas for the evolution of Raman-induced frequency shift are derived in the case of non-soliton pulses. • Dynamics of non-soliton ultrashort pulses in the cases of positive and zero group dispersion is considered. • The deceleration and the saturation of Raman-induced frequency shift are analyzed. • The calculation relies on the moment method and fit well to the numerical solution of the nonlinear wave equation.

Molecular photoelectron holography with circularly polarized laser pulses.

Science.gov (United States)

Yang, Weifeng; Sheng, Zhihao; Feng, Xingpan; Wu, Miaoli; Chen, Zhangjin; Song, Xiaohong

2014-02-10

We investigate the photoelectron momentum distribution of molecular-ion H2+driven by ultrashort intense circularly polarized laser pulses. Both numerical solutions of the time-dependent Schrödinger equation (TDSE) and a quasiclassical model indicate that the photoelectron holography (PH) with circularly polarized pulses can occur in molecule. It is demonstrated that the interference between the direct electron wave and rescattered electron wave from one core to its neighboring core induces the PH. Moreover, the results of the TDSE predict that there is a tilt angle between the interference pattern of the PH and the direction perpendicular to the molecular axis. Furthermore, the tilt angle is sensitively dependent on the wavelength of the driven circularly polarized pulse, which is confirmed by the quasiclassical calculations. The PH induced by circularly polarized laser pulses provides a tool to resolve the electron dynamics and explore the spatial information of molecular structures.

Unidirectional, dual-comb lasing under multiple pulse formation mechanisms in a passively mode-locked fiber ring laser

OpenAIRE

Liu, Ya; Zhao, Xin; Hu, Guoqing; Li, Cui; Zhao, Bofeng; Zheng, Zheng

2016-01-01

Dual-comb lasers from which asynchronous ultrashort pulses can be simultaneously generated have recently become an interesting research subject. They could be an intriguing alternative to the current dual-laser optical-frequency-comb source with highly sophisticated electronic control systems. If generated through a common light path traveled by all pulses, the common-mode noises between the spectral lines of different pulse trains could be significantly reduced. Therefore, coherent dual-comb...

Characterization of Ultrafast Laser Pulses using a Low-dispersion Frequency Resolved Optical Grating Spectrometer

Science.gov (United States)

Whitelock, Hope; Bishop, Michael; Khosravi, Soroush; Obaid, Razib; Berrah, Nora

2016-05-01

A low dispersion frequency-resolved optical gating (FROG) spectrometer was designed to characterize ultrashort (non-colinear optical parametric amplifier. This instrument splits a laser pulse into two replicas with a 90:10 intensity ratio using a thin pellicle beam-splitter and then recombines the pulses in a birefringent medium. The instrument detects a wavelength-sensitive change in polarization of the weak probe pulse in the presence of the stronger pump pulse inside the birefringent medium. Scanning the time delay between the two pulses and acquiring spectra allows for characterization of the frequency and time content of ultrafast laser pulses, that is needed for interpretation of experimental results obtained from these ultrafast laser systems. Funded by the DoE-BES, Grant No. DE-SC0012376.

Inelastic processes and interference effects during the interaction of positronium with ultrashort electromagnetic pulses

Energy Technology Data Exchange (ETDEWEB)

Eseev, M. K., E-mail: m_eseev@mail.ru; Matveev, V. I., E-mail: matveev.victor@pomorsu.ru [Lomonosov Northern (Arctic) Federal University (Russian Federation)

2013-11-15

The excitation, breakup, and reradiation during the interaction of a positronium atom with ultrashort electromagnetic pulses are considered. The probabilities of inelastic processes and reradiation spectra have been obtained. The interference between the amplitudes of the photon emission by the electron and positron is shown to contribute noticeably to the reradiation spectra. The developed approach is applicable for describing the interaction of positronium with ultrashort pulses of attosecond or shorter duration.

Picosecond and subpicosecond pulsed laser deposition of Pb thin films

Directory of Open Access Journals (Sweden)

F. Gontad

2013-09-01

Full Text Available Pb thin films were deposited on Nb substrates by means of pulsed laser deposition (PLD with UV radiation (248 nm, in two different ablation regimes: picosecond (5 ps and subpicosecond (0.5 ps. Granular films with grain size on the micron scale have been obtained, with no evidence of large droplet formation. All films presented a polycrystalline character with preferential orientation along the (111 crystalline planes. A maximum quantum efficiency (QE of 7.3×10^{-5} (at 266 nm and 7 ns pulse duration was measured, after laser cleaning, demonstrating good photoemission performance for Pb thin films deposited by ultrashort PLD. Moreover, Pb thin film photocathodes have maintained their QE for days, providing excellent chemical stability and durability. These results suggest that Pb thin films deposited on Nb by ultrashort PLD are a noteworthy alternative for the fabrication of photocathodes for superconductive radio-frequency electron guns. Finally, a comparison with the characteristics of Pb films prepared by ns PLD is illustrated and discussed.

Absorption of Ultrashort Electromagnetic Pulses on Broadened Dipole Transitions

International Nuclear Information System (INIS)

Svita, S Yu; Astapenko, V A

2014-01-01

The study is devoted to the theoretical analysis of ultrashort electromagnetic pulses (USP) absorption on broadened dipole transitions. Calculations are made in the frame of perturbation theory with the use of the basic formula for energy absorbed during all time of the action of USP on dipole transition. Dependences of absorbed energy upon pulse duration and carrier frequency are obtained and analyzed for different types of spectral line shape and USP parameters

Allowable propagation of short pulse laser beam in a plasma channel and electromagnetic solitary waves

International Nuclear Information System (INIS)

Zhang, Shan; Hong, Xue-Ren; Wang, Hong-Yu; Xie, Bai-Song

2011-01-01

Nonparaxial and nonlinear propagation of a short intense laser beam in a parabolic plasma channel is analyzed by means of the variational method and nonlinear dynamics. The beam propagation properties are classified by five kinds of behaviors. In particularly, the electromagnetic solitary wave for finite pulse laser is found beside the other four propagation cases including beam periodically oscillating with defocussing and focusing amplitude, constant spot size, beam catastrophic focusing. It is also found that the laser pulse can be allowed to propagate in the plasma channel only when a certain relation for laser parameters and plasma channel parameters is satisfied. For the solitary wave, it may provide an effective way to obtain ultra-short laser pulse.

Instantaneous nonvertical electronic transitions with shaped femtosecond laser pulses: Is it possible?

DEFF Research Database (Denmark)

Henriksen, Niels Engholm; Møller, Klaus Braagaard

2003-01-01

In molecular electronic transitions, a vertical transition can be induced by an ultrashort laser pulse. That is, a replica of the initial nuclear state-times the transition dipole moment of the electronic transition-can be created instantaneously (on the time scale of nuclear motion) in the excited...

Studying the mechanism of micromachining by short pulsed laser

Science.gov (United States)

Gadag, Shiva

The semiconductor materials like Si and the transparent dielectric materials like glass and quartz are extensively used in optoelectronics, microelectronics, and microelectromechanical systems (MEMS) industries. The combination of these materials often go hand in hand for applications in MEMS such as in chips for pressure sensors, charge coupled devices (CCD), and photovoltaic (PV) cells for solar energy generation. The transparent negative terminal of the solar cell is made of glass on one surface of the PV cell. The positive terminal (cathode) on the other surface of the solar cell is made of silicon with a glass negative terminal (anode). The digital watches and cell phones, LEDs, micro-lens, optical components, and laser optics are other examples for the application of silicon and or glass. The Si and quartz are materials extensively used in CCD and LED for digital cameras and CD players respectively. Hence, three materials: (1) a semiconductor silicon and transparent dielectrics,- (2) glass, and (3) quartz are chosen for laser micromachining as they have wide spread applications in microelectronics industry. The Q-switched, nanosecond pulsed lasers are most extensively used for micro-machining. The nanosecond type of short pulsed laser is less expensive for the end users than the second type, pico or femto, ultra-short pulsed lasers. The majority of the research work done on these materials (Si, SiO 2, and glass) is based on the ultra-short pulsed lasers. This is because of the cut quality, pin point precision of the drilled holes, formation of the nanometer size microstructures and fine features, and minimally invasive heat affected zone. However, there are many applications such as large surface area dicing, cutting, surface cleaning of Si wafers by ablation, and drilling of relatively large-sized holes where some associated heat affected zone due to melting can be tolerated. In such applications the nanosecond pulsed laser ablation of materials is very

Technical advantages of disk laser technology in short and ultrashort pulse processes

Science.gov (United States)

Graham, P.; Stollhof, J.; Weiler, S.; Massa, S.; Faisst, B.; Denney, P.; Gounaris, E.

2011-03-01

This paper demonstrates that disk-laser technology introduces advantages that increase efficiency and allows for high productivity in micro-processing in both the nanosecond (ns) and picosecond (ps) regimes. Some technical advantages of disk technology include not requiring good pump beam quality or special wavelengths for pumping of the disk, high optical efficiencies, no thermal lensing effects and a possible scaling of output power without an increase of pump beam quality. With cavity-dumping, the pulse duration of the disk laser can be specified between 30 and hundreds of nanoseconds, but is independent of frequency, thus maintaining process stability. TRUMPF uses this technology in the 750 watts average power laser TruMicro 7050. High intensity, along with fluency, is important for high ablation rates in thinfilm removal. Thus, these ns lasers show high removal rates, above 60 cm2/s, in thin-film solar cell production. In addition, recent results in paint-stripping of aerospace material prove the green credentials and high processing rates inherent with this technology as it can potentially replace toxic chemical processes. The ps disk technology meanwhile is used in, for example, scribing of solar cells, wafer dicing and drilling injector nozzles, as the pulse duration is short enough to minimize heat input in the laser-matter interaction. In the TruMicro Series 5000, the multi-pass regenerative amplifier stage combines high optical-optical efficiencies together with excellent output beam quality for pulse durations of only 6 ps and high pulse energies of up to 0.25 mJ.

Scattering of an ultrashort electromagnetic radiation pulse by an atom in a broad spectral range

International Nuclear Information System (INIS)

Astapenko, V. A.

2011-01-01

The scattering of an ultrashort electromagnetic pulse by atomic particles is described using a consistent quantum-mechanical approach taking into account excitation of a target and nondipole electromagnetic interaction, which is valid in a broad spectral range. This approach is applied to the scattering of single- and few-cycle pulses by a multielectron atom and a hydrogen atom. Scattering spectra are obtained for ultrashort pulses of different durations. The relative contribution of “elastic” scattering of a single-cycle pulse by a hydrogen atom is studied in the high-frequency limit as a function of the carrier frequency and scattering angle.

Ultrashort-pulse laser machining system employing a parametric amplifier

Science.gov (United States)

Perry, Michael D.

2004-04-27

A method and apparatus are provided for increasing the energy of chirped laser pulses to an output in the range 0.001 to over 10 millijoules at a repetition rate 0.010 to 100 kHz by using a two stage optical parametric amplifier utilizing a bulk nonlinear crystal wherein the pump and signal beam size can be independently adjusted in each stage.

Enhanced hole boring with two-color relativistic laser pulses in the fast ignition scheme

Energy Technology Data Exchange (ETDEWEB)

Yu, Changhai; Tian, Ye; Li, Wentao; Wang, Wentao; Zhang, Zhijun; Qi, Rong; Wang, Cheng [State Key Laboratory of High Field Laser Physics, Shanghai Institute of Optics and Fine Mechanics, Chinese Academy of Sciences, Shanghai 201800 (China); Deng, Aihua, E-mail: aihuadeng1985@gmail.com [Department of Physics and Astronomy, University of California, Los Angeles, California 90095 (United States); Liu, Jiansheng, E-mail: michaeljs-liu@siom.ac.cn [State Key Laboratory of High Field Laser Physics, Shanghai Institute of Optics and Fine Mechanics, Chinese Academy of Sciences, Shanghai 201800 (China); Collaborative Innovation Center of IFSA (CICIFSA), Shanghai Jiao Tong University, Shanghai 200240 (China)

2016-08-15

A scheme of using two-color laser pulses for hole boring into overdense plasma as well as energy transfer into electron and ion beams has been studied using particle-in-cell simulations. Following an ultra-short ultra-intense hole-boring laser pulse with a short central wavelength in extreme ultra-violet range, the main infrared driving laser pulse can be guided in the hollow channel preformed by the former laser and propagate much deeper into an overdense plasma, as compared to the case using the infrared laser only. In addition to efficiently transferring the main driving laser energy into energetic electrons and ions generation deep inside the overdense plasma, the ion beam divergence can be greatly reduced. The results might be beneficial for the fast ignition concept of inertial confinement fusion.

Nonlinear Theory of Nonparaxial Laser Pulse Propagation in Plasma Channels

International Nuclear Information System (INIS)

Esarey, E.; Schroeder, C. B.; Shadwick, B. A.; Wurtele, J. S.; Leemans, W. P.

2000-01-01

Nonparaxial propagation of ultrashort, high-power laser pulses in plasma channels is examined. In the adiabatic limit, pulse energy conservation, nonlinear group velocity, damped betatron oscillations, self-steepening, self-phase modulation, and shock formation are analyzed. In the nonadiabatic limit, the coupling of forward Raman scattering (FRS) and the self-modulation instability (SMI) is analyzed and growth rates are derived, including regimes of reduced growth. The SMI is found to dominate FRS in most regimes of interest. (c) 2000 The American Physical Society

Interference effects during the reradiation of ultrashort electromagnetic pulses by polyatomic systems

Energy Technology Data Exchange (ETDEWEB)

Makarov, D. N.; Matveev, V. I., E-mail: mezon98@mail.ru [Lomonosov Northern (Arctic) Federal University (Russian Federation)

2013-11-15

A theory of the reradiation of ultrashort electromagnetic pulses by arbitrary polyatomic systems of isolated complex atoms has been developed. The technique used allows the spatial inhomogeneity of the field of an ultrashort pulse and photon momenta in reradiation processes to be accurately taken into account. The angular distributions of the reradiation spectra have been obtained for an arbitrary number of atoms in the system. The processes of interference between the photon emission amplitudes are shown to give rise to characteristic “diffraction” maxima. We consider one-dimensional, two-dimensional, and three-dimensional rectangular lattices as examples as well as planar and cylindrical structures as models of planar nanosystems and nanotubes.

Optical soliton communication using ultra-short pulses

CERN Document Server

Sadegh Amiri, Iraj

2015-01-01

This brief analyzes the characteristics of a microring resonator (MRR) to perform communication using ultra-short soliton pulses. The raising of nonlinear refractive indices, coupling coefficients and radius of the single microring resonator leads to decrease in input power and round trips wherein the bifurcation occurs. As a result, bifurcation or chaos behaviors are seen at lower input power of 44 W, where the nonlinear refractive index is n2=3.2×10−20 m2/W. Using a decimal convertor system, these ultra-short signals can be converted into quantum information. Results show that multi solitons with FWHM and FSR of 10 pm and 600 pm can be generated respectively. The multi optical soliton with FWHM and FSR of 325 pm and 880 nm can be incorporated with a time division multiple access (TDMA) system wherein the transportation of quantum information is performed.

Frequency-doubled DBR-tapered diode laser for direct pumping of Ti:sapphire lasers generating sub-20 fs pulses

DEFF Research Database (Denmark)

Müller, André; Jensen, Ole Bjarlin; Unterhuber, Angelika

2011-01-01

For the first time a single-pass frequency doubled DBR-tapered diode laser suitable for pumping Ti:sapphire lasers generating ultrashort pulses is demonstrated. The maximum output powers achieved when pumping the Ti:sapphire laser are 110 mW (CW) and 82 mW (mode-locked) respectively at 1.2 W...... of pump power. This corresponds to a reduction in optical conversion efficiencies to 75% of the values achieved with a commercial diode pumped solid-state laser. However, the superior electro-optical efficiency of the diode laser improves the overall efficiency of the Ti:sapphire laser by a factor > 2....... The optical spectrum emitted by the Ti:sapphire laser when pumped with our diode laser shows a spectral width of 112 nm (FWHM). Based on autocorrelation measurements, pulse widths of less than 20 fs can therefore be expected....

Frequency-doubled DBR-tapered diode laser for direct pumping of Ti:sapphire lasers generating sub-20 fs pulses.

Science.gov (United States)

Müller, André; Jensen, Ole Bjarlin; Unterhuber, Angelika; Le, Tuan; Stingl, Andreas; Hasler, Karl-Heinz; Sumpf, Bernd; Erbert, Götz; Andersen, Peter E; Petersen, Paul Michael

2011-06-20

For the first time a single-pass frequency doubled DBR-tapered diode laser suitable for pumping Ti:sapphire lasers generating ultrashort pulses is demonstrated. The maximum output powers achieved when pumping the Ti:sapphire laser are 110 mW (CW) and 82 mW (mode-locked) respectively at 1.2 W of pump power. This corresponds to a reduction in optical conversion efficiencies to 75% of the values achieved with a commercial diode pumped solid-state laser. However, the superior electro-optical efficiency of the diode laser improves the overall efficiency of the Ti:sapphire laser by a factor > 2. The optical spectrum emitted by the Ti:sapphire laser when pumped with our diode laser shows a spectral width of 112 nm (FWHM). Based on autocorrelation measurements, pulse widths of less than 20 fs can therefore be expected.

Study of ultra-high gradient wakefield excitation by intense ultrashort laser pulses in plasma

International Nuclear Information System (INIS)

Kotaki, Hideyuki

2002-12-01

We investigate a mechanism of nonlinear phenomena in laser-plasma interaction, a laser wakefield excited by intense laser pulses, and the possibility of generating an intense bright electron source by an intense laser pulse. We need to understand and further employ some of these phenomena for our purposes. We measure self-focusing, filamentation, and the anomalous blueshift of the laser pulse. The ionization of gas with the self-focusing causes a broad continuous spectrum with blueshift. The normal blueshift depends on the laser intensity and the plasma density. We, however, have found different phenomenon. The laser spectrum shifts to fixed wavelength independent of the laser power and gas pressure above some critical power. We call the phenomenon 'anomalous blueshift'. The results are explained by the formation of filaments. An intense laser pulse can excite a laser wakefield in plasma. The coherent wakefield excited by 2 TW, 50 fs laser pulses in a gas-jet plasma around 10 18 cm -3 is measured with a time-resolved frequency domain interferometer (FDI). The density distribution of the helium gas is measured with a time-resolved Mach-Zehnder interferometer to search for the optimum laser focus position and timing in the gas-jet. The results show an accelerating wakefield excitation of 20 GeV/m with good coherency, which is useful for ultrahigh gradient particle acceleration in a compact system. This is the first time-resolved measurement of laser wakefield excitation in a gas-jet plasma. The experimental results are compared with a Particle-in-Cell (PIC) simulation. The pump-probe interferometer system of FDI and the anomalous blueshift will be modified to the optical injection system as a relativistic electron beam injector. In 1D PIC simulation we obtain the results of high quality intense electron beam acceleration. These results illuminate the possibility of a high energy and a high quality electron beam acceleration. (author)

Dynamic control of laser driven proton beams by exploiting self-generated, ultrashort electromagnetic pulses

Energy Technology Data Exchange (ETDEWEB)

Kar, S., E-mail: s.kar@qub.ac.uk; Ahmed, H.; Nersisyan, G.; Hanton, F.; Naughton, K.; Lewis, C. L. S.; Borghesi, M. [Centre for Plasma Physics, School of Mathematics and Physics, Queen' s University Belfast, Belfast BT7 1NN (United Kingdom); Brauckmann, S.; Giesecke, A. L.; Willi, O. [Institut für Laser-und Plasmaphysik, Heinrich-Heine-Universität, Düsseldorf (Germany)

2016-05-15

As part of the ultrafast charge dynamics initiated by high intensity laser irradiations of solid targets, high amplitude EM pulses propagate away from the interaction point and are transported along any stalks and wires attached to the target. The propagation of these high amplitude pulses along a thin wire connected to a laser irradiated target was diagnosed via the proton radiography technique, measuring a pulse duration of ∼20 ps and a pulse velocity close to the speed of light. The strong electric field associated with the EM pulse can be exploited for controlling dynamically the proton beams produced from a laser-driven source. Chromatic divergence control of broadband laser driven protons (upto 75% reduction in divergence of >5 MeV protons) was obtained by winding the supporting wire around the proton beam axis to create a helical coil structure. In addition to providing focussing and energy selection, the technique has the potential to post-accelerate the transiting protons by the longitudinal component of the curved electric field lines produced by the helical coil lens.

Development of high current electron source using photoemission from metals with ultrashort laser pulses

International Nuclear Information System (INIS)

Tsang, T.; Srinivasan-Rao, T.; Fischer, J.

1990-10-01

We summarize the studies of photoemission from metal photocathodes using picosecond pulses in the UV (4.66 eV) wavelength and femtosecond laser pulses in the visible (2 eV) wavelengths. To achieve high current density yield from metal photocathodes, multiphoton photoemission using femtosecond laser pulses are suggested. Electron yield improvement incorporating surface photoemission and surface plasmon resonance in metals and metal films are demonstrated. We examine the possibility of the nonlinear photoemission process overtaking the linear process, and identity some possible complexity. To extract the large amount of electrons free of space charge, a pulsed high voltage is designed; the results of the preliminary test are presented. Finally, for the first time, the width of the electron temporal profiles are measured, utilizing the nonlinear photoelectric effect, to below 100 fsec time regime. The results indicated that the electron pulse duration follows the laser pulses and are not limited by the material. 8 refs., 15 figs

Regenerative similariton laser

Directory of Open Access Journals (Sweden)

Thibault North

2016-05-01

Full Text Available Self-pulsating lasers based on cascaded reshaping and reamplification (2R are capable of initiating ultrashort pulses despite the accumulation of large amounts of nonlinearities in all-fiber resonators. The spectral properties of pulses in self-similar propagation are compatible with cascaded 2R regeneration by offset filtering, making parabolic pulses suitable for the design of a laser of this recently introduced class. A new type of regenerative laser giving birth to similaritons is numerically investigated and shows that this laser is the analog of regenerative sources based solely on self-phase modulation and offset filtering. The regenerative similariton laser does not suffer from instabilities due to excessive nonlinearities and enables ultrashort pulse generation in a simple cavity configuration.

Incubation behaviour in triazenepolymer thin films upon near-infrared femtosecond laser pulse irradiation

International Nuclear Information System (INIS)

Bonse, J; Wiggins, S M; Solis, J; Sturm, H; Urech, L; Wokaun, A; Lippert, T

2007-01-01

The effects of laser radiation induced by a sequence of ultrashort (130 fs), near-infrared (800 nm) Ti:sapphire laser pulses in ∼1 μm thick triazenepolymer films on glass substrates have been investigated by means of in-situ real-time reflectivity measurements featuring a ps-resolution streak camera and a ns-resolution photodiode set-up. The polymer films show incubation effects when each laser pulse in the sequence has a fluence below the single-pulse damage threshold. Non-damage conditions are maintained for several incubation pulses such that the reflectivity of the film shows a rapid decrease of up to 30% within 1 ns but subsequently recovers to its initial value on a ms timescale. Additional pulses lead to a permanent film damage. The critical number of laser pulses needed to generate a permanent damage of the film has been studied as a function of the laser fluence. Once damage is created, further laser pulses cause a partial removal of the film material from the glass substrate. Scanning force microscopy has been used to characterise ex-situ the irradiated surface areas. Based on these complementary measurements possible incubation mechanisms are discussed

Propagation of ultrashort laser pulses in water: linear absorption and onset of nonlinear spectral transformation.

Science.gov (United States)

Sokolov, Alexei V; Naveira, Lucas M; Poudel, Milan P; Strohaber, James; Trendafilova, Cynthia S; Buck, William C; Wang, Jieyu; Strycker, Benjamin D; Wang, Chao; Schuessler, Hans; Kolomenskii, Alexandre; Kattawar, George W

2010-01-20

We study propagation of short laser pulses through water and use a spectral hole filling technique to essentially perform a sensitive balanced comparison of absorption coefficients for pulses of different duration. This study is motivated by an alleged violation of the Bouguer-Lambert-Beer law at low light intensities, where the pulse propagation is expected to be linear, and by a possible observation of femtosecond optical precursors in water. We find that at low intensities, absorption of laser light is determined solely by its spectrum and does not directly depend on the pulse duration, in agreement with our earlier work and in contradiction to some work of others. However, as the laser fluence is increased, interaction of light with water becomes nonlinear, causing energy exchange among the pulse's spectral components and resulting in peak-intensity dependent (and therefore pulse-duration dependent) transmission. For 30 fs pulses at 800 nm center wavelength, we determine the onset of nonlinear propagation effects to occur at a peak value of about 0.12 mJ/cm(2) of input laser energy fluence.

An ultra short pulse reconstruction software applied to the GEMINI high power laser system

Energy Technology Data Exchange (ETDEWEB)

Galletti, Mario, E-mail: mario.gall22@gmail.com [INFN – LNF, Via Enrico Fermi 40, 00044 Frascati (Italy); Galimberti, Marco [Central Laser Facility, Rutherford Appleton Laboratory, Didcot (United Kingdom); Hooker, Chris [Central Laser Facility, Rutherford Appleton Laboratory, Didcot (United Kingdom); University of Oxford, Oxford (United Kingdom); Chekhlov, Oleg; Tang, Yunxin [Central Laser Facility, Rutherford Appleton Laboratory, Didcot (United Kingdom); Bisesto, Fabrizio Giuseppe [INFN – LNF, Via Enrico Fermi 40, 00044 Frascati (Italy); Curcio, Alessandro [INFN – LNF, Via Enrico Fermi 40, 00044 Frascati (Italy); Sapienza – University of Rome, P.le Aldo Moro, 2, 00185 Rome (Italy); Anania, Maria Pia [INFN – LNF, Via Enrico Fermi 40, 00044 Frascati (Italy); Giulietti, Danilo [Physics Department of the University and INFN, Pisa (Italy)

2016-09-01

The GRENOUILLE traces of Gemini pulses (15 J, 30 fs, PW, shot per 20 s) were acquired in the Gemini Target Area PetaWatt at the Central Laser Facility (CLF), Rutherford Appleton Laboratory (RAL). A comparison between the characterizations of the laser pulse parameters made using two different types of algorithms: Video Frog and GRenouille/FrOG (GROG), was made. The temporal and spectral parameters came out to be in great agreement for the two kinds of algorithms. In this experimental campaign it has been showed how GROG, the developed algorithm, works as well as VideoFrog algorithm with the PetaWatt pulse class. - Highlights: • Integration of the diagnostic tool on high power laser. • Validation of the GROG algorithm in comparison to a well-known commercial available software. • Complete characterization of the GEMINI ultra-short high power laser pulse.

KrF laser ablation of a polyethersulfone film: Effect of pulse duration on structure formation

International Nuclear Information System (INIS)

Pazokian, Hedieh; Selimis, Alexandros; Stratakis, Emmanuel; Mollabashi, Mahmoud; Barzin, Jalal; Jelvani, Saeid

2011-01-01

Polyethersulfone (PES) films were processed with KrF laser irradiation of different pulse durations (τ). Scanning electron microscopy (SEM) and Raman spectroscopy were employed for the examination of the morphology and chemical composition of the irradiated surfaces, respectively. During ablation with 500 fs and 5 ps pulses, localized deformations (beads), micro-ripple and conical structures were observed on the surface depending on the irradiation fluence (F) and the number of pulses (N). In addition, the number density of the structures is affected by the irradiation parameters (τ, F, N). Furthermore, at longer pulse durations (τ = 30 ns), conical structures appear at lower laser fluence values, which are converted into columnar structures upon irradiation at higher fluences. The Raman spectra collected from the top of the structures following irradiation at different pulse durations revealed graphitization of the ns laser treated areas, in contrast to those processed with ultra-short laser pulses.

Ultrashort electromagnetic clusters formation by two-stream superheterodyne free electron lasers

DEFF Research Database (Denmark)

Kulish, Viktor V.; Lysenko, Alexander V.; Volk, Iurii I.

2016-01-01

A cubic nonlinear self-consistent theory of multiharmonic two-stream superheterodyne free electron lasers (TSFEL) of a klystron type, intended to form powerful ultrashort clusters of an electromagnetic field is constructed. Plural three-wave parametric resonant interactions of wave harmonics have...... been taken into account. An amplitude, phase and spectral analyses of the processes occurring in such devices have been carried out. The conditions necessary for the forming of the ultrashort clusters of an electromagnetic field have been found out. The possibility of the ultrashort electromagnetic...

Superfocusing of an ultrashort plasmon pulse by a conducting cone

Energy Technology Data Exchange (ETDEWEB)

Manuilovich, E S; Astapenko, V A [Moscow Institute of Physics and Technology (State University), Dolgoprudnyi, Moscow Region (Russian Federation); Golovinskii, P A [Voronezh State University of Architecture and Civil Engineering, Voronezh (Russian Federation)

2016-01-31

We have shown theoretically the possibility of controlling nanoscale superfocusing of plasmons in a metal conical tip by modulating the carrier frequency of the pulse. The propagation of an ultrashort plasmon pulse in a metal nanoneedle is simulated numerically. The calculation is based on an asymptotic analytical solution of Maxwell's equations for electromagnetic wave propagation in a conical conductor in the vicinity of its apex, obtained by the approximate separation of variables in spherical coordinates. The dependence the field superfocusing on the conductor material, pulse chirp and propagation length is studied. (nanooptics)

Magnetization reversal in ultrashort magnetic field pulses

International Nuclear Information System (INIS)

Bauer, M.; Lopusnik, R.; Fassbender, J.; Hillebrands, B.

2000-01-01

We report the switching properties of a thin magnetic film subject to an ultrashort, laterally localized magnetic field pulse, obtained by numerical investigations. The magnetization distribution in the film is calculated on a grid assuming Stoner-like coherent rotation within the grid square size. Perpendicularly and in-plane magnetized films exhibit a magnetization reversal due to a 4 ps magnetic field pulse. Outside the central region the pulse duration is short compared to the precession period. In this area the evolution of the magnetization during the field pulse does not depend strongly on magnetic damping and/or pulse shape. However, the final magnetization distribution is affected by the magnetic damping. Although the pulse duration is short compared to the precession period, the time needed for the relaxation of the magnetization to the equilibrium state is rather large. The influence of the different magnetic anisotropy contributions and the magnetic damping parameter enters into the magnetization reversal process. Comparing the case of perpendicular anisotropy with different kinds of in-plane anisotropies, a principal difference is found due to the symmetry of the shape anisotropy with respect to the anisotropy in question

Histological observation on dental hard tissue irradiated by ultrashort-pulsed laser

Science.gov (United States)

Uchizono, Takeyuki; Awazu, Kunio; Igarashi, Akihiro; Kato, Junji; Hirai, Yoshito

2006-04-01

In the field of dentistry, effectiveness of USPL irradiation is researched because USPL has less thermal side effect to dental hard tissue. In this paper, we observed morphological change and optical change of dental hard tissue irradiated by USPL for discussing the safety and effectiveness of USPL irradiation to dental hard tissues. Irradiated samples were crown enamel and root dentin of bovine teeth. Lasers were Ti:sapphire laser, which had pulse duration (P d)of 130 fsec and pulse repetition rate (f) of 1kHz and wavelength (l) of 800nm, free electron laser (FEL), which had P d of 15 μsec and f of 10Hz and wavelength of 9.6μm, and Er:YAG laser, which had P d of 250 μsec and f of 10Hz and wavelength of 2.94μm. After laser irradiation, the sample surfaces and cross sections were examined with SEM and EDX. The optical change of samples was observed using FTIR. In SEM, the samples irradiated by USPL had sharp and accurate ablation with no crack and no carbonization. But, in FEL and Er:YAG laser, the samples has rough ablation with crack and carbonization. It was cleared that the P/Ca ratio of samples irradiated by USPL had same value as non-irradiated samples. There was no change in the IR absorption spectrum between samples irradiated by USPL and non-irradiated sample. But, they of samples irradiated by FEL and Er:YAG laser, however, had difference value as non-irradiated samples. These results showed that USPL might be effective to ablate dental hard tissue without thermal damage.

Q-switched all-fiber laser with short pulse duration based on tungsten diselenide

Science.gov (United States)

Li, Wenyi; OuYang, Yuyi; Ma, Guoli; Liu, Mengli; Liu, Wenjun

2018-05-01

Fiber lasers are widely used in industrial processing, sensing, medical and communications applications due to their simple structure, good stability and low cost. With the rapid development of fiber lasers and the sustained improvement of industrial laser quality requirements, researchers in ultrafast optics focus on how to get laser pulses with high output power and narrow pulse duration. Q-switched technology is one of the most effective techniques to generate ultrashort pulses. In this paper, a tungsten diselenide saturable absorber with 16.82% modulation depth is prepared by chemical vapor deposition. Experimental results show that when the pump power changes from 115.7 mW to 630 mW, the all-fiber laser can achieve a stable Q-switched pulse output. The repetition rate of the output pulse varies from 80.32 kHz to 204.2 kHz, the pulse duration is 581 ns, the maximum output power is 17.1 mW and the maximum pulse energy is 83.7 nJ. Results in this paper show that tungsten diselenide can be applied to ultrafast optics, which is a kind of saturable absorption material with excellent properties.

High-order harmonics from an ultraintense laser pulse propagating inside a fiber

International Nuclear Information System (INIS)

Bulanov, S.V.; Esirkepov, T. Zh.; Naumova, N.M.; Sokolov, I.V.

2003-01-01

A strong effect of high harmonic radiation during the propagation of a high intensity short laser pulse in a thin wall hollow channel ('fiber') is found and studied via relativistic particle-in-cell simulations. The fiber has finite width walls comprised of an overdense plasma. Only the harmonic radiation with the harmonic number above critical value, for which the fiber walls are transparent, propagates outwards in the form of a coherent ultrashort pulse with very short wavelength

Short-pulse optical parametric chirped-pulse amplification for the generation of high-power few-cycle pulses

International Nuclear Information System (INIS)

Major, Zs.; Osterhoff, J.; Hoerlein, R.; Karsch, S.; Fuoloep, J.A.; Krausz, F.; Ludwig-Maximilians Universitaet, Muenchen

2006-01-01

Complete test of publication follows. In the quest for a way to generate ultrashort, high-power, few-cycle laser pulses the discovery of optical parametric amplification (OPA) has opened up to the path towards a completely new regime, well beyond that of conventional laser amplification technology. The main advantage of this parametric amplification process is that it allows for an extremely broad amplification bandwidth compared to any known laser amplifier medium. When combined with the chirped-pulse amplification (CPA) principle (i.e. OPCPA), on one hand pulses of just 10 fs duration and 8 mJ pulse energy have been demonstrated. On the other hand, pulse energies of up to 30 J were also achieved on a different OPCPA system; the pulse duration in this case, however, was 100 fs. In order to combine ultrashort pulse durations (i.e. pulses in the few-cycle regime) with high pulse energies (i.e. in the Joule range) we propose tu pump on OPCPA chain with TW-scale short pulses (100 fs - 1 ps instead of > 100 ps of previous OPCPA systems) delivered by a conventional CPA system. This approach inherently improves the conditions for generating high-power ultrashort pulses using OPCPA in the following ways. Firstly, the short pump pulse duration reduces the necessary stretching factor for the seed pulse, thereby increasing stretching and compression fidelity. Secondly, also due to the shortened pump pulse duration, a much higher contrast is achieved. Finally, the significantly increased pump power makes the use of thinner OPCPA crystals possible, which implies an even broader amplification bandwidth, thereby allowing for even shorter pulses. We carried out theoretical investigations to show the feasibility of such a set-up. Alongside these studies we will also present preliminary experimental results of an OPCPA system pumped by the output of our Ti:Sapphire ATLAS laser, currently delivering 350 mJ in 43 fs. An insight into the planned scaling of this technique to petawatt

Efficient optical trapping of CdTe quantum dots by femtosecond laser pulses

KAUST Repository

Chiang, Weiyi

2014-12-11

The development in optical trapping and manipulation has been showing rapid progress, most of it is in the small particle sizes in nanometer scales, substituting the conventional continuous-wave lasers with high-repetition-rate ultrashort laser pulse train and nonlinear optical effects. Here, we evaluate two-photon absorption in optical trapping of 2.7 nm-sized CdTe quantum dots (QDs) with high-repetition-rate femtosecond pulse train by probing laser intensity dependence of both Rayleigh scattering image and the two-photon-induced luminescence spectrum of the optically trapped QDs. The Rayleigh scattering imaging indicates that the two-photon absorption (TPA) process enhances trapping ability of the QDs. Similarly, a nonlinear increase of the two-photon-induced luminescence with the incident laser intensity fairly indicates the existence of the TPA process.

Electron Acceleration and the Propagation of Ultrashort High-Intensity Laser Pulses in Plasmas

International Nuclear Information System (INIS)

Wang, Xiaofang; Krishnan, Mohan; Saleh, Ned; Wang, Haiwen; Umstadter, Donald

2000-01-01

Reported are interactions of high-intensity laser pulses (λ=810 nm and I≤3x10 18 W /cm 2 ) with plasmas in a new parameter regime, in which the pulse duration (τ=29 fs ) corresponds to 0.6-2.6 plasma periods. Relativistic filamentation is observed to cause laser-beam breakup and scattering of the beam out of the vacuum propagation angle. A beam of megaelectronvolt electrons with divergence angle as small as 1 degree sign is generated in the forward direction, which is correlated to the growth of the relativistic filamentation. Raman scattering, however, is found to be much less than previous long-pulse results. (c) 2000 The American Physical Society

Technique for long and absolute distance measurement based on laser pulse repetition frequency sweeping

Science.gov (United States)

Castro Alves, D.; Abreu, Manuel; Cabral, A.; Jost, Michael; Rebordão, J. M.

2017-11-01

In this work we present a technique to perform long and absolute distance measurements based on mode-locked diode lasers. Using a Michelson interferometer, it is possible to produce an optical cross-correlation between laser pulses of the reference arm with the pulses from the measurement arm, adjusting externally their degree of overlap either changing the pulse repetition frequency (PRF) or the position of the reference arm mirror for two (or more) fixed frequencies. The correlation of the travelling pulses for precision distance measurements relies on ultra-short pulse durations, as the uncertainty associated to the method is dependent on the laser pulse width as well as on a highly stable PRF. Mode-locked Diode lasers are a very appealing technology for its inherent characteristics, associated to compactness, size and efficiency, constituting a positive trade-off with regard to other mode-locked laser sources. Nevertheless, main current drawback is the non-availability of frequency-stable laser diodes. The laser used is a monolithic mode-locked semiconductor quantum-dot (QD) laser. The laser PRF is locked to an external stabilized RF reference. In this work we will present some of the preliminary results and discuss the importance of the requirements related to laser PRF stability in the final metrology system accuracy.

Electron localization in fragmentation of H2 with CEP stabilized laser pulses

International Nuclear Information System (INIS)

Kremer, Manuel; Fischer, Bettina; Schroeter, Claus Dieter; Feuerstein, Bernold; Moshammer, Robert; Ullrich, Joachim; Rudenko, Artem; Jesus, Vitor L B de

2009-01-01

Fully differential data on ionization and dissociation of H 2 in ultra-short (∼ 6 fs), linearly polarized, intense (∼ 4 . 10 14 W/cm 2 ) laser pulses with stabilized carrier-envelope-phase (CEP) have been measured using a reaction microscope. Depending on the CEP of the laser pulses we see a clear asymmetry in the emission direction of the created protons. Contrary to earlier measurements by Kling et al. we observe the highest asymmetry for kinetic energy releases (proton energy) between 0-2 eV. This excludes the electron re-collision mechanism suggested in [1] as dominant excitation channel and requires another explanation.

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

Vacuum ultraviolet Ar2*laser pumped by a high-intensity laser

International Nuclear Information System (INIS)

Kubodera, Shoichi; Kaku, Masanori; Higashiguchi, Takeshi

2004-01-01

We observed a small-signal gain of Ar 2 * emission at 126 nm by use of an Ar-filled hollow fiber to guide the ultrashort-pulse high-intensity laser propagation. The small signal gain coefficient was measured to be 0.05 cm -1 at 126 nm. Kinetic analysis revealed that the electrons produced by the high-intensity laser through an optical-field ionization process initiated the Ar 2 * production process. This laser scheme could be combined with high harmonic radiation of the pump laser in the vacuum ultraviolet (VUV), leading to the production of amplified ultrashort VUV pulses. (author)

Fullerene-reduced graphene oxide composites obtained by ultrashort laser ablation of fullerite in water

Energy Technology Data Exchange (ETDEWEB)

De Bonis, A., E-mail: angela.debonis@unibas.it [Dipartimento di Scienze, Università degli Studi della Basilicata, Viale dell’Ateneo Lucano, 10-85100, Potenza (Italy); Curcio, M. [Dipartimento di Scienze, Università degli Studi della Basilicata, Viale dell’Ateneo Lucano, 10-85100, Potenza (Italy); Santagata, A. [CNR-ISM, U.O.S. Tito Scalo, Zona Industriale, 85050, Tito Scalo (PZ) (Italy); Rau, J.V. [CNR-ISM, Via del Fosso del Cavaliere, 100-00133, Rome (Italy); Galasso, A.; Teghil, R. [Dipartimento di Scienze, Università degli Studi della Basilicata, Viale dell’Ateneo Lucano, 10-85100, Potenza (Italy)

2015-05-01

Highlights: • Laser ablation of a fullerite target in water performed by an ultra-short laser source has been reported. • The formation of reduced graphene oxide has been described considering the laser ablation in liquid mechanism. • Fullerene-reduced graphene oxide composite, in the form of self assembled microtubes, has been described. - Abstract: The laser ablation in liquid of carbon-based solid targets is of particular interest thanks to the possibility of obtaining different carbon allotropes by varying the experimental parameters employed. The ablation of a fullerite target in water using a frequency-doubled Nd:glass laser source with a pulse duration of 250 fs and a frequency repetition rate of 10 Hz is presented. The obtained products have been characterized by transmission electron and atomic force microscopies and by X-ray photoelectron and micro-Raman spectroscopies. During the femtosecond laser ablation, the collapse of fullerene cages has been considered with the consequent formation of graphene oxide (GO) and its successive hydrogenation. The process of self-assembling in microtube structures of the formed reduced graphene oxide-fullerene composites has then been reported.

Quantum interference metrology at deep-UV wavelengths using phase-controlled ultrashort laser pulses

NARCIS (Netherlands)

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

2005-01-01

High-resolution metrology at wavelengths shorter than ultraviolet is in general hampered by a limited availability of appropriate laser sources. It is demonstrated that this limitation can be overcome by quantum-interference metrology with frequency up-converted ultrafast laser pulses. The required

Study of the interaction between heavy ions and integrated circuits using a pulsed laser beam

International Nuclear Information System (INIS)

Lewis, D.; Fouillat, P.; Pouget, V.; Lapuyade, H.

2002-01-01

A new pulsed laser beam equipment dedicated to the characterization of integrated circuit is presented. Using ultra-short laser pulses is a convenient way to simulate experimentally the spatial environment of integrated circuits when interactions with heavy ions occur. This experimental set-up can be considered as a complementary tool for particle accelerators to evaluate the hardness assurance of integrated circuits for space applications. These particles generate temporally electrical disturbance called Single Event Effect (SEE). The theoretical approach of an equivalence between heavy ions and a laser pulses is discussed. The experimental set-up and some relevant operational methodologies are presented. Experimental results demonstrate that the induced electrical responses due to an heavy ion or a laser pulse are quite similar. Some sensitivity mappings of integrated circuits provided by this test bench illustrate the capabilities and the limitations of this laser-based technique. Contrary to the particle accelerators, it provides useful information concerning the spatial and temporal dependences of SEE mechanisms. (authors)

Third-harmonic generation and self-channeling in air using high-power femtosecond laser pulses

International Nuclear Information System (INIS)

Akoezbek, N.; Iwasaki, A.; Chin, S.L.; Becker, A.; Scalora, M.; Bowden, C.M.

2002-01-01

It is shown, both theoretically and experimentally, that during laser pulse filamentation in air an intense ultrashort third-harmonic pulse is generated forming a two-colored filament. The third-harmonic pulse maintains both its peak intensity and energy over distances much longer than the characteristic coherence length. We argue that this is due to a nonlinear phase-locking mechanism between the two pulses in the filament and is independent of the initial material wave-vector mismatch. A rich spatiotemporal propagation dynamics of the third-harmonic pulse is predicted. Potential applications of this phenomenon to other parametric processes are discussed

Generation of ultra-intense and ultra-short laser pulses with high temporal contrast

International Nuclear Information System (INIS)

Julien, A.

2006-03-01

The topic of this thesis work concerns the design and the characterization of an efficient device devoted to the temporal contrast improvement for ultra-intense femtosecond laser pulses. The contrast is defined as the intensity ratio between the main femtosecond pulse and its nanosecond pedestal. This pedestal is the amplified spontaneous emission (ASE), inherent with laser amplification mechanism. The ASE background has dramatic effects for laser-matter interactions on a solid target. The presented work consists in the theoretical and experimental study of a temporal filter based on a third order nonlinear effect acting on the pulse polarization. We have studied several kinds of nonlinear filters. The selected device is based on the process of cross-polarized wave generation (XPW) in crystals with an anisotropic third-order nonlinear susceptibility. This nonlinear filter has been experimented on various femtosecond systems. It allows a contrast improvement of several orders of magnitude, as demonstrated by temporal profiles measurements on a large intensity dynamic. A device to improve the nonlinear process conversion efficiency, it means the filter transmission, has also been achieved. This method is based on constructive interferences between XPW signals generated in different crystals. This setup has made it possible to reach experimentally the maximum theoretical efficiency ( >20%) and in the same time ensures the system stability. At least, we have demonstrated that the filter preserves, or even improves, spectral and spatial qualities of the laser pulse. These results are thus particularly promising and allow contemplating the implementation of the filter in current femtosecond systems. (author)

Ultrashort-pulse-train pump and dump excitation of a diatomic molecule

Science.gov (United States)

de Araujo, Luís E. E.

2010-09-01

An excitation scheme is proposed for transferring population between ground-vibrational levels of a molecule. The transfer is accomplished by pumping and dumping population with a pair of coherent ultrashort-pulse trains via a stationary state. By mismatching the teeth of the frequency combs associated with the pulse trains to the vibrational levels, high selectivity in the excitation, along with high transfer efficiency, is predicted. The pump-dump scheme does not suffer from spontaneous emission losses, it is insensitive to the pump-dump-train delay, and it requires only basic pulse shaping.

Ultrashort-pulse-train pump and dump excitation of a diatomic molecule

OpenAIRE

de Araujo, LEE

2010-01-01

An excitation scheme is proposed for transferring population between ground-vibrational levels of a molecule. The transfer is accomplished by pumping and dumping population with a pair of coherent ultrashort-pulse trains via a stationary state. By mismatching the teeth of the frequency combs associated with the pulse trains to the vibrational levels, high selectivity in the excitation, along with high transfer efficiency, is predicted. The pump-dump scheme does not suffer from spontaneous emi...

Correction of echo shift in reconstruction processing for ultra-short TE pulse sequence

International Nuclear Information System (INIS)

Takizawa, Masahiro; Ootsuka, Takehiro; Abe, Takayuki; Takahashi, Tetsuhiko

2010-01-01

An ultra-short echo time (TE) pulse sequence is composed of a radial sampling that acquires echo signals radially in the K-space and a half-echo acquisition that acquires only half of the echo signal. The shift in the position of the echo signal (echo shift) caused by the timing errors in the gradient magnetic field pulses affects the image quality in the radial sampling with the half-echo acquisition. To improve image quality, we have developed a signal correction algorithm that detects and eliminates this echo shift during reconstruction by performing a pre-scan within 10 seconds. The results showed that image quality is improved under oblique and/or off-centering conditions that frequently cause image distortion due to hardware error. In conclusion, we have developed a robust ultra-short TE pulse sequence that allows wide latitude in the scan parameters, including oblique and off-centering conditions. (author)

Propagation of three-dimensional bipolar ultrashort electromagnetic pulses in an inhomogeneous array of carbon nanotubes

Science.gov (United States)

Fedorov, Eduard G.; Zhukov, Alexander V.; Bouffanais, Roland; Timashkov, Alexander P.; Malomed, Boris A.; Leblond, Hervé; Mihalache, Dumitru; Rosanov, Nikolay N.; Belonenko, Mikhail B.

2018-04-01

We study the propagation of three-dimensional (3D) bipolar ultrashort electromagnetic pulses in an inhomogeneous array of semiconductor carbon nanotubes. The heterogeneity is represented by a planar region with an increased concentration of conduction electrons. The evolution of the electromagnetic field and electron concentration in the sample are governed by the Maxwell's equations and continuity equation. In particular, nonuniformity of the electromagnetic field along the axis of the nanotubes is taken into account. We demonstrate that depending on values of the parameters of the electromagnetic pulse approaching the region with the higher electron concentration, the pulse is either reflected from the region or passes it. Specifically, our simulations demonstrate that after interacting with the higher-concentration area, the pulse can propagate steadily, without significant spreading. The possibility of such ultrashort electromagnetic pulses propagating in arrays of carbon nanotubes over distances significantly exceeding characteristic dimensions of the pulses makes it possible to consider them as 3D solitons.

A search for the sulphur hexafluoride cation with intense, few cycle laser pulses

Energy Technology Data Exchange (ETDEWEB)

Dota, Krithika; Mathur, Deepak, E-mail: atmol1@tifr.res.in [Tata Institute of Fundamental Research, 1 Homi Bhabha Road, Mumbai 400 005 (India); Centre for Atomic and Molecular Physics, Manipal University, Manipal 576 104 (India); Dharmadhikari, Aditya K. [Tata Institute of Fundamental Research, 1 Homi Bhabha Road, Mumbai 400 005 (India); Dharmadhikari, Jayashree A. [Centre for Atomic and Molecular Physics, Manipal University, Manipal 576 104 (India); Patra, Kaustuv; Tiwari, Ashwani K. [Indian Institute of Science Education and Research - Kolkata, Mohanpur 741 252 (India)

2013-11-21

It is well established that upon ionization of sulphur hexafluoride, the SF{sub 6}{sup +} ion is never observed in mass spectra. Recent work with ultrashort intense laser pulses has offered indications that when strong optical field are used, the resulting “bond hardening” can induce changes in the potential energy surfaces of molecular cations such that molecular ions that are normally unstable may, indeed, become metastable enough to enable their detection by mass spectrometry. Do intense, ultrashort laser pulses permit formation of SF{sub 6}{sup +}? We have utilized intense pulses of 5 fs, 11 fs, and 22 fs to explore this possibility. Our results are negative: no evidence is discovered for SF{sub 6}{sup +}. However, multiply charged sulphur and fluorine ions from highly charged SF{sub 6}{sup q+} ions are observed that enable us to resolve the controversy regarding the kinetic energy release accompanying formation of F{sup +} fragment ions. Quantum chemical computations of field-distorted potential energy curves of SF{sub 6} and its molecular ion enable us to rationalize our non-observation of SF{sub 6}{sup +}. Our findings have implications for high harmonic generation from SF{sub 6} in the few-cycle regime.

Laser cutting of bone tissue under bulk water with a pulsed ps-laser at 532 nm.

Science.gov (United States)

Tulea, Cristian-Alexander; Caron, Jan; Gehlich, Nils; Lenenbach, Achim; Noll, Reinhard; Loosen, Peter

2015-10-01

Hard-tissue ablation was already investigated for a broad variety of pulsed laser systems, which cover almost the entire range of available wavelengths and pulse parameters. Most effective in hard-tissue ablation are Er:YAG and CO2 lasers, both utilizing the effect of absorption of infrared wavelengths by water and so-called explosive vaporization, when a thin water film or water–air spray is supplied. The typical flow rates and the water layer thicknesses are too low for surgical applications where bleeding occurs and wound flushing is necessary. We studied a 20 W ps-laser with 532 nm wavelength and a pulse energy of 1 mJ to effectively ablate bones that are submerged 14 mm under water. For these laser parameters, the plasma-mediated ablation mechanism is dominant. Simulations based on the blow-off model predict the cut depth and cross-sectional shape of the incision. The model is modified considering the cross section of the Gaussian beam, the incident angle, and reflections. The ablation rate amounts to 0.2  mm3/s, corresponding to an increase by at least 50% of the highest values published so far for ultrashort laser ablation of hard tissue.

High-Average-Power Diffraction Pulse-Compression Gratings Enabling Next-Generation Ultrafast Laser Systems

Energy Technology Data Exchange (ETDEWEB)

Alessi, D. [Lawrence Livermore National Lab. (LLNL), Livermore, CA (United States)

2016-11-01

Pulse compressors for ultrafast lasers have been identified as a technology gap in the push towards high peak power systems with high average powers for industrial and scientific applications. Gratings for ultrashort (sub-150fs) pulse compressors are metallic and can absorb a significant percentage of laser energy resulting in up to 40% loss as well as thermal issues which degrade on-target performance. We have developed a next generation gold grating technology which we have scaled to the petawatt-size. This resulted in improvements in efficiency, uniformity and processing as compared to previous substrate etched gratings for high average power. This new design has a deposited dielectric material for the grating ridge rather than etching directly into the glass substrate. It has been observed that average powers as low as 1W in a compressor can cause distortions in the on-target beam. We have developed and tested a method of actively cooling diffraction gratings which, in the case of gold gratings, can support a petawatt peak power laser with up to 600W average power. We demonstrated thermo-mechanical modeling of a grating in its use environment and benchmarked with experimental measurement. Multilayer dielectric (MLD) gratings are not yet used for these high peak power, ultrashort pulse durations due to their design challenges. We have designed and fabricated broad bandwidth, low dispersion MLD gratings suitable for delivering 30 fs pulses at high average power. This new grating design requires the use of a novel Out Of Plane (OOP) compressor, which we have modeled, designed, built and tested. This prototype compressor yielded a transmission of 90% for a pulse with 45 nm bandwidth, and free of spatial and angular chirp. In order to evaluate gratings and compressors built in this project we have commissioned a joule-class ultrafast Ti:Sapphire laser system. Combining the grating cooling and MLD technologies developed here could enable petawatt laser systems to

Standard measurement procedures for the characterization of fs-laser optical components

Science.gov (United States)

Starke, Kai; Ristau, Detlev; Welling, Herbert

2003-05-01

Ultra-short pulse laser systems are considered as promising tools in the fields of precise micro-machining and medicine applications. In the course of the development of reliable table top laser systems, a rapid growth of ultra-short pulse applications could be observed during the recent years. The key for improving the performance of high power laser systems is the quality of the optical components concerning spectral characteristics, optical losses and the power handling capability. In the field of ultra-short pulses, standard measurement procedures in quality management have to be validated in respect to effects induced by the extremely high peak power densities. The present work, which is embedded in the EUREKA-project CHOCLAB II, is predominantly concentrated on measuring the multiple-pulse LIDT (ISO 11254-2) in the fs-regime. A measurement facility based on a Ti:Sapphire-CPA system was developed to investigate the damage behavior of optical components. The set-up was supplied with an improved pulse energy detector discriminating the influence of pulse-to-pulse energy fluctuations on the incidence of damage. Aditionally, a laser-calorimetric measurement facility determining the absorption (ISO 11551) utilizing a fs-Ti:Sapphire laser was accomplished. The investigation for different pulse durations between 130 fs and 1 ps revealed a drastic increase of absorption in titania coatings for ultra-short pulses.

Effects of ultrashort laser pulses on angular distributions of photoionization spectra.

Science.gov (United States)

Ooi, C H Raymond; Ho, W L; Bandrauk, A D

2017-07-27

We study the photoelectron spectra by intense laser pulses with arbitrary time dependence and phase within the Keldysh framework. An efficient semianalytical approach using analytical transition matrix elements for hydrogenic atoms in any initial state enables efficient and accurate computation of the photoionization probability at any observation point without saddle point approximation, providing comprehensive three dimensional photoelectron angular distribution for linear and elliptical polarizations, that reveal the intricate features and provide insights on the photoionization characteristics such as angular dispersions, shift and splitting of photoelectron peaks from the tunneling or above threshold ionization(ATI) regime to non-adiabatic(intermediate) and multiphoton ionization(MPI) regimes. This facilitates the study of the effects of various laser pulse parameters on the photoelectron spectra and their angular distributions. The photoelectron peaks occur at multiples of 2ħω for linear polarization while  odd-ordered peaks are suppressed in the direction perpendicular to the electric field. Short pulses create splitting and angular dispersion where the peaks are strongly correlated to the angles. For MPI and elliptical polarization with shorter pulses the peaks split into doublets and the first peak vanishes. The carrier envelope phase(CEP) significantly affects the ATI spectra while the Stark effect shifts the spectra of intermediate regime to higher energies due to interference.

Ultrashort-pulse measurement using noninstantaneous nonlinearities: Raman effects in frequency-resolved optical gating

International Nuclear Information System (INIS)

DeLong, K.W.; Ladera, C.L.; Trebino, R.; Kohler, B.; Wilson, K.R.

1995-01-01

Ultrashort-pulse-characterization techniques generally require instantaneously responding media. We show that this is not the case for frequency-resolved optical gating (FROG). We include, as an example, the noninstantaneous Raman response of fused silica, which can cause errors in the retrieved pulse width of as much as 8% for a 25-fs pulse in polarization-gate FROG. We present a modified pulse-retrieval algorithm that deconvolves such slow effects and use it to retrieve pulses of any width. In experiments with 45-fs pulses this algorithm achieved better convergence and yielded a shorter pulse than previous FROG algorithms

Ultra-short coherent terahertz radiation from ultra-short dips in electron bunches circulating in a storage ring

International Nuclear Information System (INIS)

Yamamoto, N.; Shimada, M.; Adachi, M.; Zen, H.; Tanikawa, T.; Taira, Y.; Kimura, S.; Hosaka, M.; Takashima, Y.; Takahashi, T.; Katoh, M.

2011-01-01

Terahertz (THz) coherent synchrotron radiation (CSR) is emitted not only from ultra-short electron bunches, but also from electron bunches with micro-structures. Formation of micro-structures at the sub-picosecond scale in electron bunches by a laser slicing technique is experimentally studied through observation of the THz CSR. The THz CSR spectrum was found to depend strongly on the intensity and the pulse width of the laser. The results agreed qualitatively with a numerical simulation. It was suggested that the evolution of the micro-structure during CSR emission is important under some experimental conditions.

Resonant multiphoton ionization of caesium atoms by ultra-short laser pulses at 1.06 μm

International Nuclear Information System (INIS)

Lompre, L.A.; Mainfray, G.; Manus, C.; Thebault, J.

1978-01-01

This paper reports the four-photon ionization of caesium atoms when the laser frequency is tuned through the resonant three-photon transition 6S → 6F. This experiment was performed by using a tunable-wavelength bandwidth-limited subnanosecond laser pulse at 1.06 μm, in the 10 8 -10 9 W.cm -2 laser intensity range. Pulse widths of 1.5 ns, 50 ps, and 15 ps were used. The resonant character of the multiphoton ionization process was observed, even with the shortest pulse of 15 ps. Nevertheless the influence of a temporal effect is demonstrated according to theoretical predictions. The resonance shift ΔE of the 6S → 6F transition energy was found to be linear with the laser intensity I within the range 10 8 -10 9 W.cm -2 . ΔE = αI, with α = 2 cm -1 /GW.cm -2 . This results confirms previous measurements performed with single-mode 35 ns laser pulses and is in very good agreement with calculated resonance shifts

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

Generation of “gigantic” ultra-short microwave pulses based on passive mode-locking effect in electron oscillators with saturable absorber in the feedback loop

International Nuclear Information System (INIS)

Ginzburg, N. S.; Denisov, G. G.; Vilkov, M. N.; Zotova, I. V.; Sergeev, A. S.

2016-01-01

A periodic train of powerful ultrashort microwave pulses can be generated in electron oscillators with a non-linear saturable absorber installed in the feedback loop. This method of pulse formation resembles the passive mode-locking widely used in laser physics. Nevertheless, there is a specific feature in the mechanism of pulse amplification when consecutive energy extraction from different fractions of a stationary electron beam takes place due to pulse slippage over the beam caused by the difference between the wave group velocity and the electron axial velocity. As a result, the peak power of generated “gigantic” pulses can exceed not only the level of steady-state generation but also, in the optimal case, the power of the driving electron beam.

Numerical analysis of breakdown dynamics dependence on pulse width in laser-induced damage in fused silica: Role of optical system

Directory of Open Access Journals (Sweden)

Kholoud A. Hamam

2018-06-01

Full Text Available We report a numerical investigation of the breakdown and damage in fused silica caused by ultra-short laser pulses. The study based on a modified model (Gaabour et al., 2012 that solves the rate equation numerically for the electron density evolution during the laser pulse, under the combined effect of both multiphoton and electron impact ionization processes. Besides, electron loss processes due to diffusion out of the focal volume and recombination are also considered in this analysis. The model is applied to investigate the threshold intensity dependence on laser pulse width in the experimental measurements that are given by Liu et al. (2005. In this experiment, a Ti-sapphire laser source operating at 800 nm with pulse duration varies between 240 fs and 2.5 ps is used to irradiate a bulk of fused silica with dimensions 10 × 5 × 3 mm. The laser beam was focused into the bulk using two optical systems with effective numerical apertures (NA 0.126 and 0.255 to give beam spot radius at the focus of the order 2.0 μm and 0.95 μm respectively. Reasonable agreement between the calculated thresholds and the measured ones is attained. Moreover, a study is performed to examine the respective role of the physical processes of the breakdown of fused silica in relation to the pulse width and focusing optical system. The analysis revealed a real picture of the location and size of the generated plasma. Keywords: Ultra-short laser pulses, Ablation mechanisms, Electron density, Electron loss processes, Avalanche ionization, Breakdown threshold

The Application of Cryogenic Laser Physics to the Development of High Average Power Ultra-Short Pulse Lasers

Directory of Open Access Journals (Sweden)

David C. Brown

2016-01-01

Full Text Available Ultrafast laser physics continues to advance at a rapid pace, driven primarily by the development of more powerful and sophisticated diode-pumping sources, the development of new laser materials, and new laser and amplification approaches such as optical parametric chirped-pulse amplification. The rapid development of high average power cryogenic laser sources seems likely to play a crucial role in realizing the long-sought goal of powerful ultrafast sources that offer concomitant high peak and average powers. In this paper, we review the optical, thermal, thermo-optic and laser parameters important to cryogenic laser technology, recently achieved laser and laser materials progress, the progression of cryogenic laser technology, discuss the importance of cryogenic laser technology in ultrafast laser science, and what advances are likely to be achieved in the near-future.

Application of the ultrashort pulses in bovine dental enamel; Aplicacao de pulsos ultracurtos em esmalte dental bovino

Energy Technology Data Exchange (ETDEWEB)

Todescan, Carla de Rago

2003-07-01

The interaction of lasers with the hard structures of the teeth, has found the excess of heat as a problem for its utilization. This study analyzes, in vitro, the interaction of the ultrashort pulse laser of Ti:safire (830 nm) with the bovine dental enamel. The system consisted in one main oscillator integrated with an amplifier (CPA). The pulses extracted before the temporal compression inside the amplifier had 30 ps, 1000 Hz and {approx}1 mJ. The pulses extracted after the compression had 60 fs, 1000 Hz and {approx}0,7 mJ. The M{sup 2} was 1,3, the focal lens 2,5 cm, the focal distance 29,7 and a computerized translation stage x,y,z. We evaluated the amount of tissue removed per pulse,the resulting cavities and the surrounding tissues not irradiated, under OM and SEM. The fluency was the major factor for differentiating the two regimens studied, therefore, the intensity was not so important as we expected in this process. We found: one ablation region in 'cat tongue', one ablation length, one fluency {approx}0,7 J/cm{sup 2} for 30 ps and {approx}0,5 J/cm{sup 2} for 60 fs (50% of high speed burr), smooth edge for 30 ps and high precision of the sharp edge cut of submicrometric order for 60 fs. (author)

Application of the ultrashort pulses in bovine dental enamel; Aplicacao de pulsos ultracurtos em esmalte dental bovino

Energy Technology Data Exchange (ETDEWEB)

Todescan, Carla de Rago

2003-07-01

The interaction of lasers with the hard structures of the teeth, has found the excess of heat as a problem for its utilization. This study analyzes, in vitro, the interaction of the ultrashort pulse laser of Ti:safire (830 nm) with the bovine dental enamel. The system consisted in one main oscillator integrated with an amplifier (CPA). The pulses extracted before the temporal compression inside the amplifier had 30 ps, 1000 Hz and {approx}1 mJ. The pulses extracted after the compression had 60 fs, 1000 Hz and {approx}0,7 mJ. The M{sup 2} was 1,3, the focal lens 2,5 cm, the focal distance 29,7 and a computerized translation stage x,y,z. We evaluated the amount of tissue removed per pulse,the resulting cavities and the surrounding tissues not irradiated, under OM and SEM. The fluency was the major factor for differentiating the two regimens studied, therefore, the intensity was not so important as we expected in this process. We found: one ablation region in 'cat tongue', one ablation length, one fluency {approx}0,7 J/cm{sup 2} for 30 ps and {approx}0,5 J/cm{sup 2} for 60 fs (50% of high speed burr), smooth edge for 30 ps and high precision of the sharp edge cut of submicrometric order for 60 fs. (author)

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.

Ablation of burned skin with ultra-short pulses laser to promote healing: evaluation by optical coherence tomography, histology, μATR-FTIR and Nonlinear Microscopy

International Nuclear Information System (INIS)

Santos, Moises Oliveira dos

2012-01-01

Burns cause changes in the anatomical structure of the skin associated with trauma. The severity of the burn injury is divided into first, second and third-degree burns. The third-degree burns have been a major focus of research in search of more conservative treatments and faster results in repair for a functional and cosmetically acceptable. The conventional treatment is the use of topical natural or synthetic skin graft. An alternative therapy is the laser ablation process for burned tissue necrosis removal due to the no mechanical contact, fast application and access to difficult areas. The purpose of this study is to evaluate the feasibility of using high intensity femtosecond lasers as an adjunct treatment of burned patients. For this study, 65 Wistar rats were divided into groups of five animals: healthy skin, burned skin, two types of treatment (surgical debridement or femtosecond laser ablation) and four different times in the healing process monitoring. Three regions of the back of the animals were exposed to steam source causing third-degree burn. On the third day after the burn, one of the regions was ablated with high intensity ultrashort laser pulses (λ = 785 nm, 90 fs, 2 kHz and 10 μJ/ pulse), the other received surgical debridement, and the last was considered the burn control. The regions were analyzed by optical coherence tomography (OCT), histology, attenuated total reflectance infrared spectroscopy using Fourier transform (μ-ATR-FTIR), two-photon excitation fluorescence microscopy (TPEFM) and second harmonic generation technique (SHG) on days 3, 5, 7 and 14 pos-treatments. The results showed that with the laser irradiation conditions used it was possible to remove debris from third degree burn. The techniques used to characterize the tissue allowed to verify that all treatments promoted wound healing. On the fourteenth day, the regeneration curve showed that the attenuation coefficient of laser ablated tissue converges to the values of

An ultrashort-pulse reconstruction software: GROG, applied to the FLAME laser system

Science.gov (United States)

Galletti, Mario

2016-03-01

The GRENOUILLE traces of FLAME Probe line pulses (60mJ, 10mJ after compression, 70fs, 1cm FWHM, 10Hz) were acquired in the FLAME Front End Area (FFEA) at the Laboratori Nazionali di Frascati (LNF), Instituto Nazionale di Fisica Nucleare (INFN). The complete characterization of the laser pulse parameters was made using a new algorithm: GRenouille/FrOG (GROG). A characterization with a commercial algorithm, QUICKFrog, was also made. The temporal and spectral parameters came out to be in great agreement for the two kinds of algorithms. In this experimental campaign the Probe line of FLAME has been completely characterized and it has been showed how GROG, the developed algorithm, works as well as QuickFrog algorithm with this type of pulse class.

Simulation study on cross polarization scattering of ultrashort-pulse electromagnetic waves

International Nuclear Information System (INIS)

Katsuragawa, Naoki; Hojo, Hitoshi; Mase, Atushi

1996-11-01

Simulation study on cross polarization scattering of ultrashort-pulse electromagnetic waves due to magnetic fluctuations is presented. One-dimensional coupled wave equations for the ordinary and extraordinary modes are solved for incident unipolar sub-cycle pulses in an inhomogeneous magnetized plasma. It is shown that the peak frequencies in the frequency-spectral signals of the mode-converted reflected waves are determined from the Bragg resonance condition in the wave numbers of the ordinary mode, the extraordinary mode and the magnetic fluctuations for relatively short-wavelength localized magnetic fluctuations. (author)

Fabrication of porous biopolymer substrates for cell growth by UV laser: The role of pulse duration

International Nuclear Information System (INIS)

Castillejo, Marta; Rebollar, Esther; Oujja, Mohamed; Sanz, Mikel; Selimis, Alexandros; Sigletou, Maria; Psycharakis, Stelios; Ranella, Anthi; Fotakis, Costas

2012-01-01

Highlights: ► UV laser-induced superficial foaming in biopolymer films with fs, ps and ns pulses. ► Reduction of photochemical and structural modifications by ultrashort fs irradiation. ► Successful cell culture on laser-induced foam structure generated in chitosan. - Abstract: Ultraviolet laser irradiation using pulses with duration from the nanosecond to the femtosecond range was investigated aiming at the generation of a foam layer on films of the biopolymers chitosan, starch and their blend. We report on the morphological characteristics of the foams obtained upon irradiation and on the accompanying laser induced photochemistry, assessed by on line monitoring of the laser induced fluorescence. We identify the laser conditions (pulse duration) at which foaming is produced and discuss the obtained results in reference to the material properties, particularly extinction coefficient and thermal parameters. This article also reports on successful cell culture on the laser induced foam structure generated in chitosan, as an illustrative example of the possibility of broader use of laser induced biopolymer foaming structures in biology.

Influence of chirp on laser-pulse amplification in Brillouin backscattering schemes

Science.gov (United States)

Lehmann, Goetz; Schluck, Friedrich; Spatschek, Karl-Heinz

2015-11-01

Plasma-based amplification of laser pulses is currently discussed as a key component for the next generation of high-intensity laser systems, possibly enabling the generation of ultra-short pulses in the exawatt-zetawatt regime. In these scenarios the energy of a long pump pulse (several ps to ns of duration) is transferred to a short seed pulse via a plasma oscillation. Weakly- and strongly-coupled (sc) Brillouin backscattering have been identified as potential candidates for robust amplification scenarios. With the help of three-wave interaction models, we investigate the influence of a chirp of the pump beam on the seed amplification. We show that chirp can mitigate deleterious spontaneous Raman backscattering of the pump off noise and that at the same time the amplification dynamics due to Brillouin scattering is still intact. For the experimentally very interesting case of sc-Brillouin we find a dependence of the efficiency on the sign of the chirp. Funding provided by project B10 of SFB TR18 of the Deutsche Forschungsgemeinschaft (DFG).

Plasma-enhanced chemical vapor deposition of aluminum oxide using ultrashort precursor injection pulses

NARCIS (Netherlands)

Dingemans, G.; Sanden, van de M.C.M.; Kessels, W.M.M.

2012-01-01

An alternative plasma-enhanced chemical vapor deposition (PECVD) method is developed and applied for the deposition of high-quality aluminum oxide (AlOx) films. The PECVD method combines a continuous plasma with ultrashort precursor injection pulses. We demonstrate that the modulation of the

Decoration of silica nanowires with gold nanoparticles through ultra-short pulsed laser deposition

Science.gov (United States)

Gontad, F.; Caricato, A. P.; Cesaria, M.; Resta, V.; Taurino, A.; Colombelli, A.; Leo, C.; Klini, A.; Manousaki, A.; Convertino, A.; Rella, R.; Martino, M.; Perrone, A.

2017-10-01

The ablation of a metal target at laser energy densities in the range of 1-10 TW/cm2 leads to the generation of nanoparticles (NP) of the ablated material. This aspect is of particular interest if the immobilization of NPs on three-dimensional (3D) substrates is necessary as for example in sensing applications. In this work the deposition of Au NP by irradiation of a Au bulk target with a sub-picosecond laser beam (500 fs; 248 nm; 10 Hz) on 2D (silica and Si(100)) and 3D substrates (silica nanowire forests) is reported for different number of laser pulses (500, 1000, 1500, 2000, 2500). A uniform coverage of small Au NPs (with a diameter of few nm) on both kinds of substrates has been obtained using a suitable number of laser pulses. The presence of spherical droplets, with a diameter ranging from tens of nm up to few μm was also detected on the substrate surface and their presence can be explained by the weak electron-phonon coupling of Au. The optical characterization of the samples on 2D and 3D substrates evidenced the surface plasmon resonance peak characteristic of the Au NPs although further improvements of the size-distribution are necessary for future applications in sensing devices.

Imaging Electron Dynamics with Ultrashort Light Pulses: A Theory Perspective

Directory of Open Access Journals (Sweden)

Daria Popova-Gorelova

2018-02-01

Full Text Available A wide range of ultrafast phenomena in various atomic, molecular and condense matter systems is governed by electron dynamics. Therefore, the ability to image electronic motion in real space and real time would provide a deeper understanding of such processes and guide developments of tools to control them. Ultrashort light pulses, which can provide unprecedented time resolution approaching subfemtosecond time scale, are perspective to achieve real-time imaging of electron dynamics. This task is challenging not only from an experimental view, but also from a theory perspective, since standard theories describing light-matter interaction in a stationary regime can provide erroneous results in an ultrafast case as demonstrated by several theoretical studies. We review the theoretical framework based on quantum electrodynamics, which has been shown to be necessary for an accurate description of time-resolved imaging of electron dynamics with ultrashort light pulses. We compare the results of theoretical studies of time-resolved nonresonant and resonant X-ray scattering, and time- and angle-resolved photoelectron spectroscopy and show that the corresponding time-resolved signals encode analogous information about electron dynamics. Thereby, the information about an electronic system provided by these time-resolved techniques is different from the information provided by their time-independent analogues.

Determination of ultra-short laser induced damage threshold of KH2PO4 crystal: Numerical calculation and experimental verification

Directory of Open Access Journals (Sweden)

Jian Cheng

2016-03-01

Full Text Available Rapid growth and ultra-precision machining of large-size KDP (KH2PO4 crystals with high laser damage resistance are tough challenges in the development of large laser systems. It is of high interest and practical significance to have theoretical models for scientists and manufacturers to determine the laser-induced damage threshold (LIDT of actually prepared KDP optics. Here, we numerically and experimentally investigate the laser-induced damage on KDP crystals in ultra-short pulse laser regime. On basis of the rate equation for free electron generation, a model dedicated to predicting the LIDT is developed by considering the synergistic effect of photoionization, impact ionization and decay of electrons. Laser damage tests are performed to measure the single-pulse LIDT with several testing protocols. The testing results combined with previously reported experimental data agree well with those calculated by the model. By taking the light intensification into consideration, the model is successfully applied to quantitatively evaluate the effect of surface flaws inevitably introduced in the preparation processes on the laser damage resistance of KDP crystals. This work can not only contribute to further understanding of the laser damage mechanisms of optical materials, but also provide available models for evaluating the laser damage resistance of exquisitely prepared optical components used in high power laser systems.

Atomic and Molecular Systems in Intense Ultrashort Laser Pulses

Science.gov (United States)

Saenz, A.

2008-07-01

The full quantum mechanical treatment of atomic and molecular systems exposed to intense laser pulses is a so far unsolved challenge, even for systems as small as molecular hydrogen. Therefore, a number of simplified qualitative and quantitative models have been introduced in order to provide at least some interpretational tools for experimental data. The assessment of these models describing the molecular response is complicated, since a comparison to experiment requires often a number of averages to be performed. This includes in many cases averaging of different orientations of the molecule with respect to the laser field, focal volume effects, etc. Furthermore, the pulse shape and even the peak intensity is experimentally not known with very high precision; considering, e.g., the exponential intensity dependence of the ionization signal. Finally, experiments usually provide only relative yields. As a consequence of all these averagings and uncertainties, it is possible that different models may successfully explain some experimental results or features, although these models disagree substantially, if their predictions are compared before averaging. Therefore, fully quantum-mechanical approaches at least for small atomic and molecular systems are highly desirable and have been developed in our group. This includes efficient codes for solving the time-dependent Schrodinger equation of atomic hydrogen, helium or other effective one- or two-electron atoms as well as for the electronic motion in linear (effective) one-and two-electron diatomic molecules like H_2.Very recently, a code for larger molecular systems that adopts the so-called single-active electron approximation was also successfully implemented and applied. In the first part of this talk popular models describing intense laser-field ionization of atoms and their extensions to molecules are described. Then their validity is discussed on the basis of quantum-mechanical calculations. Finally, some

Ultrafast lasers for precise and corrosion free marking on chirurgical steels

Science.gov (United States)

Neugebauer, Christoph; Aalderink, Dennis; Maurer, Erich; Faisst, Birgit; Budnicki, Aleksander

2017-02-01

The unique properties of ultrashort laser pulses and the decrease of invest pave the way to numerous novel applications. Even in the very price sensitive field of laser marking, ultrashort laser can compete due to a new cost structure and remarkable properties of the marking results. In this study we concentrated on industrial marking of medical equipment by using IR ultrashort lasers and compared the results with common marking laser systems. We demonstrate the benefits of ultrashort lasers marking on chirurgical devices, observing the influence of pulse energy, pulse duration, scanning velocity in respect to the visibility, corrosion resistance and long term durability under clinical conditions. Nowadays many parts and products are marked for the purpose of identification and traceability. One kind of laser marking is the well known annealing of stainless steel by nanosecond marking lasers. When annealing occurs a colored oxide layer grows due to the local heating of the material surface. Compared to the raw material, the annealed marking shows increased corrosion sensitivity. Regarding the traceability, the poor durability of the ns marking resulting in contrast reduction and the corrosion susceptibility are a huge problem. Therefore three different laser sources with ns-psfs pulse duration were observed. The focus rests on the realization of parameter studies (various lasers) and their effect on the corrosion and passivation behavior. Furthermore analysis of the oxide layers by use of EDX and XRD were performed to obtain further information on the composition and structure of the markings.

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

Efficient chirped-pulse amplification of sub-20 fs laser pulses

Energy Technology Data Exchange (ETDEWEB)

Matsuoka, Shinichi; Yamakawa, Koichi [Japan Atomic Energy Research Inst., Tokai, Ibaraki (Japan). Tokai Research Establishment

1998-03-01

We have developed a model for ultrabroadband and ultrashort pulse amplification including the effects of a pulse shaper for regenerative pulse shaping, gain narrowing and gain saturation in the amplifiers. Thin solid etalons are used to control both gain narrowing and gain saturation during amplification. This model has been used to design an optimized Ti:sapphire amplifier system for producing efficiently pulses of < 20-fs duration with approaching peak and average powers of 100 TW and 20 W. (author)

Multiplex CARS imaging with spectral notch shaped laser pulses delivered by optical fibers.

Science.gov (United States)

Oh, Seung Ryeol; Park, Joo Hyun; Kim, Kyung-Soo; Lee, Jae Yong; Kim, Soohyun

2017-12-11

We present an experimental demonstration of single-pulse coherent anti-Stokes Raman spectroscopy (CARS) using a spectrally shaped broadband laser that is delivered by an optical fiber to a sample at its distal end. The optical fiber consists of a fiber Bragg grating component to serve as a narrowband notch filter and a combined large-mode-area fiber to transmit such shaped ultrashort laser pulses without spectral distortion in a long distance. Experimentally, our implementation showed a capability to measure CARS spectra of various samples with molecular vibrations in the fingerprint region. Furthermore, CARS imaging of poly(methyl methacrylate) bead samples was carried out successfully under epi-CARS geometry in which backward-scattered CARS signals were collected into a multimode optical fiber. A compatibility of single-pulse CARS scheme with fiber optics, verified in this study, implies a potential for future realization of compact all-fiber CARS spectroscopic imaging systems.

Unidirectional, dual-comb lasing under multiple pulse formation mechanisms in a passively mode-locked fiber ring laser

Science.gov (United States)

Liu, Ya; Zhao, Xin; Hu, Guoqing; Li, Cui; Zhao, Bofeng; Zheng, Zheng

2016-09-01

Dual-comb lasers from which asynchronous ultrashort pulses can be simultaneously generated have recently become an interesting research subject. They could be an intriguing alternative to the current dual-laser optical-frequency-comb source with highly sophisticated electronic control systems. If generated through a common light path traveled by all pulses, the common-mode noises between the spectral lines of different pulse trains could be significantly reduced. Therefore, coherent dual-comb generation from a completely common-path, unidirectional lasing cavity would be an interesting territory to explore. In this paper, we demonstrate such a dual-comb lasing scheme based on a nanomaterial saturable absorber with additional pulse narrowing and broadening mechanisms concurrently introduced into a mode-locked fiber laser. The interactions between multiple soliton formation mechanisms result in unusual bifurcation into two-pulse states with quite different characteristics. Simultaneous oscillation of pulses with four-fold difference in pulsewidths and tens of Hz repetition rate difference is observed. The coherence between these spectral-overlapped, picosecond and femtosecond pulses is further verified by the corresponding asynchronous cross-sampling and dual-comb spectroscopy measurements.

Quasi-monoenergetic proton acceleration from cryogenic hydrogen microjet by ultrashort ultraintense laser pulses

Science.gov (United States)

Sharma, A.; Tibai, Z.; Hebling, J.; Fülöp, J. A.

2018-03-01

Laser-driven proton acceleration from a micron-sized cryogenic hydrogen microjet target is investigated using multi-dimensional particle-in-cell simulations. With few-cycle (20-fs) ultraintense (2-PW) laser pulses, high-energy quasi-monoenergetic proton acceleration is predicted in a new regime. A collisionless shock-wave acceleration mechanism influenced by Weibel instability results in a maximum proton energy as high as 160 MeV and a quasi-monoenergetic peak at 80 MeV for 1022 W/cm2 laser intensity with controlled prepulses. A self-generated strong quasi-static magnetic field is also observed in the plasma, which modifies the spatial distribution of the proton beam.

Accurate and efficient implementation of the von Neumann representation for laser pulses with discrete and finite spectra

International Nuclear Information System (INIS)

Dimler, Frank; Fechner, Susanne; Rodenberg, Alexander; Brixner, Tobias; Tannor, David J

2009-01-01

We recently introduced the von Neumann picture, a joint time-frequency representation, for describing ultrashort laser pulses. The method exploits a discrete phase-space lattice of nonorthogonal Gaussians to represent the pulses; an arbitrary pulse shape can be represented on this lattice in a one-to-one manner. Although the representation was originally defined for signals with an infinite continuous spectrum, it can be adapted to signals with discrete and finite spectrum with great computational savings, provided that discretization and truncation effects are handled with care. In this paper, we present three methods that avoid loss of accuracy due to these effects. The approach has immediate application to the representation and manipulation of femtosecond laser pulses produced by a liquid-crystal mask with a discrete and finite number of pixels.

Probing spatial properties of electronic excitation in water after interaction with temporally shaped femtosecond laser pulses: Experiments and simulations

Energy Technology Data Exchange (ETDEWEB)

Winkler, Thomas; Sarpe, Cristian; Jelzow, Nikolai [Institute of Physics and CINSaT, University of Kassel, Heinrich-Plett-Str. 40, D-34132 Kassel (Germany); Lillevang, Lasse H. [Department of Physics and Astronomy, Aarhus University, Ny Munkegade 120, DK-8000 Aarhus C (Denmark); Götte, Nadine; Zielinski, Bastian [Institute of Physics and CINSaT, University of Kassel, Heinrich-Plett-Str. 40, D-34132 Kassel (Germany); Balling, Peter [Department of Physics and Astronomy, Aarhus University, Ny Munkegade 120, DK-8000 Aarhus C (Denmark); Senftleben, Arne [Institute of Physics and CINSaT, University of Kassel, Heinrich-Plett-Str. 40, D-34132 Kassel (Germany); Baumert, Thomas, E-mail: baumert@physik.uni-kassel.de [Institute of Physics and CINSaT, University of Kassel, Heinrich-Plett-Str. 40, D-34132 Kassel (Germany)

2016-06-30

Highlights: • Temporally asymmetric shaped femtosecond laser pulses lead to excitation over smaller area and larger depth in water. • Transient optical properties are measured radially resolved by spectral interference in an imaging geometry. • Radially resolved spectral interference shows indications of nonlinear propagation effects at high fluences. - Abstract: In this work, laser excitation of water under ambient conditions is investigated by radially resolved common-path spectral interferometry. Water, as a sample system for dielectric materials, is excited by ultrashort bandwidth-limited and temporally asymmetric shaped femtosecond laser pulses, where the latter start with an intense main pulse followed by a decaying pulse sequence, i.e. a temporal Airy pulse. Spectral interference in an imaging geometry allows measurements of the transient optical properties integrated along the propagation through the sample but radially resolved with respect to the transverse beam profile. Since the optical properties reflect the dynamics of the free-electron plasma, such measurements reveal the spatial characteristics of the laser excitation. We conclude that temporally asymmetric shaped laser pulses are a promising tool for high-precision laser material processing, as they reduce the transverse area of excitation, but increase the excitation inside the material along the beam propagation.

Method and apparatus for improving the quality and efficiency of ultrashort-pulse laser machining

Science.gov (United States)

Stuart, Brent C.; Nguyen, Hoang T.; Perry, Michael D.

2001-01-01

A method and apparatus for improving the quality and efficiency of machining of materials with laser pulse durations shorter than 100 picoseconds by orienting and maintaining the polarization of the laser light such that the electric field vector is perpendicular relative to the edges of the material being processed. Its use is any machining operation requiring remote delivery and/or high precision with minimal collateral dames.

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 ...

Table-top laser-driven ultrashort electron and X-ray source: the CIBER-X source project

Science.gov (United States)

Girardeau-Montaut, Jean-Pierre; Kiraly, Bélà; Girardeau-Montaut, Claire; Leboutet, Hubert

2000-09-01

We report on the development of a new laser-driven table-top ultrashort electron and X-ray source, also called the CIBER-X source . X-ray pulses are produced by a three-step process which consists of the photoelectron emission from a thin metallic photocathode illuminated by 16 ps duration laser pulses at 213 nm. The e-gun is a standard Pierce diode electrode type, in which electrons are accelerated by a cw electric field of ˜11 MV/m up to a hole made in the anode. The photoinjector produces a train of 70-80 keV electron pulses of ˜0.5 nC and 20 A peak current at a repetition rate of 10 Hz. The electrons are then transported outside the diode along a path of 20 cm length, and are focused onto a target of thullium by magnetic fields produced by two electromagnetic coils. X-rays are then produced by the impact of electrons on the target. Simulations of geometrical, electromagnetic fields and energetic characteristics of the complete source were performed previously with the assistance of the code PIXEL1 also developed at the laboratory. Finally, experimental electron and X-ray performances of the CIBER-X source as well as its application to very low dose imagery are presented and discussed. source Compacte d' Impulsions Brèves d' Electrons et de Rayons X

Table-top laser-driven ultrashort electron and X-ray source: the CIBER-X source project

Energy Technology Data Exchange (ETDEWEB)

Girardeau-Montaut, J.-P. E-mail: jean-pierre.girardeau@univ-lyonl.fr; Kiraly, Bela; Girardeau-Montaut, Claire; Leboutet, Hubert

2000-09-21

We report on the development of a new laser-driven table-top ultrashort electron and X-ray source, also called the CIBER-X source . X-ray pulses are produced by a three-step process which consists of the photoelectron emission from a thin metallic photocathode illuminated by 16 ps duration laser pulses at 213 nm. The e-gun is a standard Pierce diode electrode type, in which electrons are accelerated by a cw electric field of {approx}11 MV/m up to a hole made in the anode. The photoinjector produces a train of 70-80 keV electron pulses of {approx}0.5 nC and 20 A peak current at a repetition rate of 10 Hz. The electrons are then transported outside the diode along a path of 20 cm length, and are focused onto a target of thulium by magnetic fields produced by two electromagnetic coils. X-rays are then produced by the impact of electrons on the target. Simulations of geometrical, electromagnetic fields and energetic characteristics of the complete source were performed previously with the assistance of the code PIXEL1 also developed at the laboratory. Finally, experimental electron and X-ray performances of the CIBER-X source as well as its application to very low dose imagery are presented and discussed.

Femtosecond laser spectroscopy

CERN Document Server

Hannaford, Peter

2005-01-01

As concepts and methodologies have evolved over the past two decades, the realm of ultrafast science has become vast and exciting and has impacted many areas of chemistry, biology and physics, and other fields such as materials science, electrical engineering, and optical communication. The field has recently exploded with the announcement of a series of remarkable new developments and advances. This volume surveys this recent growth in eleven chapters written by leading international researchers in the field. It includes sections on femtosecond optical frequency combs, soft x-ray femtosecond laser sources, and attosecond laser sources. In addition, the contributors address real-time spectroscopy of molecular vibrations with sub-5-fs pulses and multidimensional femtosecond coherent spectroscopies for studying molecular and electron dynamics. Novel methods for measuring and characterizing ultrashort laser pulses and ultrashort pulses of light are also described. The topics covered are revolutionizing the field...

Time resolved studies of H2+ dissociation with phase-stabilized laser pulses

International Nuclear Information System (INIS)

Fischer, Bettina

2010-01-01

In the course of this thesis, experimental studies on the dissociation of H 2 + (H 2 + →p+H) in ultrashort laser pulses with a stabilized carrier-envelope phase (CEP) were carried out. In single-pulse measurements, the ability to control the emission direction of low energetic protons, i.e. the localization of the bound electron at one of the nuclei after dissociation, by the CEP was demonstrated. The coincident detection of the emitted protons and electrons and the measurement of their three-dimensional momentum vectors with a reaction microscope allowed to clarify the localization mechanism. Further control was achieved by a pump-control scheme with two timedelayed CEP-stabilized laser pulses. Here the neutral H 2 molecule was ionized in the first pulse and dissociation was induced by the second pulse. Electron localization was shown to depend on the properties of the bound nuclear wave packet in H 2 + at the time the control pulse is applied, demonstrating the ability to use the shape and dynamics of the nuclear wave packet as control parameters. Wave packet simulations were performed reproducing qualitatively the experimental results of the single and the two-pulse measurements. For both control schemes, intuitive models are presented, which qualitatively explain the main features of the obtained results. (orig.)

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.

Expansion-limited aggregation of nanoclusters in a single-pulse laser-produced plume

International Nuclear Information System (INIS)

Gamaly, E. G.; Madsen, N. R.; Rode, A. V.; Golberg, D.

2009-01-01

Formation of carbon nanoclusters in a single-laser-pulse created ablation plume was studied both in vacuum and in a noble gas environment at various pressures. The developed theory provides cluster radius dependence on combination of laser parameters, properties of ablated material, and type and pressure of an ambient gas in agreement with experiments. The experiments were performed on carbon nanoclusters formed by laser ablation of graphite targets with 12 picosecond 532 nm laser pulses at MHz-range repetition rate in a broad range of ambient He, Ar, Kr, and Xe gas pressures from 2x10 -2 to 1500 Torr. The experimental results confirmed our theoretical prediction that the average size of the nanoparticles depends weakly on the type of the ambient gas used, and is determined exclusively by the single laser pulse parameters even at the repetition rate as high as 28 MHz with the time gap 36 ns between the pulses. The most important finding relates to the fact that in vacuum the cluster size is mainly determined by hydrodynamic expansion of the plume while in the ambient gas it is controlled by atomic diffusion in the gas. We demonstrate that the ultrashort pulses can be used for production of clusters with the size less than the critical value, which separates the particles with properties drastically different from those of a material in a bulk. The presented results of experiments on formation of carbon nanoclusters are in close agreement with the theoretical scaling. The developed theory is applicable for cluster formation from any monatomic material, such as silicon for example.

Investigation of ultrashort pulse laser ablation of solid targets by measuring the ablation-generated momentum using a torsion pendulum.

Science.gov (United States)

Zhang, Nan; Wang, Wentao; Zhu, Xiaonong; Liu, Jiansheng; Xu, Kuanhong; Huang, Peng; Zhao, Jiefeng; Li, Ruxin; Wang, Mingwei

2011-04-25

50 fs - 12 ps laser pulses are employed to ablate aluminum, copper, iron, and graphite targets. The ablation-generated momentum is measured with a torsion pendulum. Corresponding time-resolved shadowgraphic measurements show that the ablation process at the optimal laser fluence achieving the maximal momentum is primarily dominated by the photomechanical mechanism. When laser pulses with specific laser fluence are used and the pulse duration is tuned from 50 fs to 12 ps, the generated momentum firstly increases and then remains almost constant, which could be attributed to the change of the ablation mechanism involved from atomization to phase explosion. The investigation of the ablation-generated momentum also reveals a nonlinear momentum-energy conversion scaling law, namely, as the pulse energy increases, the momentum obtained by the target increases nonlinearly. This may be caused by the effective reduction of the dissipated energy into the surrounding of the ablation zone as the pulse energy increases, which indicates that for femtosecond laser the dissipated energy into the surrounding target is still significant.

Formation of metal nanoparticles of various sizes in plasma plumes produced by Ti:sapphire laser pulses

International Nuclear Information System (INIS)

Chakravarty, U.; Naik, P. A.; Mukherjee, C.; Kumbhare, S. R.; Gupta, P. D.

2010-01-01

In this paper, an experimental study on generation of nanoparticle various sizes using Ti:sapphire laser pulses, is reported. Nanoparticle formation in plasma plumes of metals like silver and copper, expanding in vacuum, has been studied using stretched pulses of 300 ps duration [subnanoseconds (sub-ns)] from a Ti:sapphire laser. It has been compared with the nanoparticle formation (of the same materials) when compressed pulses of 45 fs duration were used under similar focusing conditions. Nanoparticle formation is observed at intensities as high as 2x10 16 W/cm 2 . The structural analysis of the nanoparticle deposition on a silicon substrate showed that, using 45 fs pulses, smaller nanoparticles of average size ∼20 nm were generated, whereas on using the sub-ns pulses, larger particles were produced. Also, the visible light transmission and reflection from the nanoparticle film of Ag on glass substrate showed surface plasmon resonance (SPR). The SPR curves of the films of nanoparticles deposited by femtosecond pulses were always broader and reflection/transmission was always smaller when compared with the films formed using the sub-ns pulses, indicating smaller size particle formation by ultrashort pulses. Thus, it has been demonstrated that variation in the laser pulse duration of laser offers a simple tool for varying the size of the nanoparticles generated in plasma plumes.

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.

Laser-assisted electron scattering in strong-field ionization of dense water vapor by ultrashort laser pulses

International Nuclear Information System (INIS)

Wilke, M; Al-Obaidi, R; Moguilevski, A; Kothe, A; Engel, N; Metje, J; Kiyan, I Yu; Aziz, E F

2014-01-01

We report on strong-field ionization of dense water gas in a short infrared laser pulse. By employing a unique combination of photoelectron spectroscopy with a liquid micro-jet technique, we observe how the character of electron emission at high kinetic energies changes with the increase of the medium density. This change is associated with the process of laser-assisted electron scattering (LAES) on neighboring particles, which becomes a dominant mechanism of hot electron emission at higher medium densities. The manifestation of this mechanism is found to require densities that are orders of magnitude lower than those considered for heating the laser-generated plasmas via the LAES process. The experimental results are supported by simulations of the LAES yield with the use of the Kroll–Watson theory. (paper)

Impacts of ambient and ablation plasmas on short- and ultrashort-pulse laser processing of surfaces

Czech Academy of Sciences Publication Activity Database

Bulgakova, Nadezhda M.; Panchenko, A.N.; Zhukov, V.P.; Kudryashov, S.I.; Pereira, A.; Marine, W.; Mocek, Tomáš; Bulgakov, A.V.

2014-01-01

Roč. 5, č. 4 (2014), s. 1344-1372 ISSN 2072-666X R&D Projects: GA MŠk ED2.1.00/01.0027; GA MŠk EE2.3.20.0143 Grant - others:HILASE(XE) CZ.1.05/2.1.00/01.0027; OP VK 6(XE) CZ.1.07/2.3.00/20.0143 Institutional support: RVO:68378271 Keywords : pulsed laser ablation * laser material processing * laser plasma * ambient gas breakdown * material redeposition * plasma pipe formation * microstructures Subject RIV: BH - Optics, Masers, Lasers Impact factor: 1.269, year: 2014

Determination of ultra-short laser induced damage threshold of KH{sub 2}PO{sub 4} crystal: Numerical calculation and experimental verification

Energy Technology Data Exchange (ETDEWEB)

Cheng, Jian [Center for Precision Engineering, School of Mechatronics Engineering, Harbin Institute of Technology, Harbin 150001 (China); Department of Physics, The Ohio State University, 191 W. Woodruff Ave, Columbus, OH 43210 (United States); Chen, Mingjun, E-mail: chenmj@hit.edu.cn, E-mail: chowdhury.24@osu.edu; Wang, Jinghe; Xiao, Yong [Center for Precision Engineering, School of Mechatronics Engineering, Harbin Institute of Technology, Harbin 150001 (China); Kafka, Kyle; Austin, Drake; Chowdhury, Enam, E-mail: chenmj@hit.edu.cn, E-mail: chowdhury.24@osu.edu [Department of Physics, The Ohio State University, 191 W. Woodruff Ave, Columbus, OH 43210 (United States)

2016-03-15

Rapid growth and ultra-precision machining of large-size KDP (KH{sub 2}PO{sub 4}) crystals with high laser damage resistance are tough challenges in the development of large laser systems. It is of high interest and practical significance to have theoretical models for scientists and manufacturers to determine the laser-induced damage threshold (LIDT) of actually prepared KDP optics. Here, we numerically and experimentally investigate the laser-induced damage on KDP crystals in ultra-short pulse laser regime. On basis of the rate equation for free electron generation, a model dedicated to predicting the LIDT is developed by considering the synergistic effect of photoionization, impact ionization and decay of electrons. Laser damage tests are performed to measure the single-pulse LIDT with several testing protocols. The testing results combined with previously reported experimental data agree well with those calculated by the model. By taking the light intensification into consideration, the model is successfully applied to quantitatively evaluate the effect of surface flaws inevitably introduced in the preparation processes on the laser damage resistance of KDP crystals. This work can not only contribute to further understanding of the laser damage mechanisms of optical materials, but also provide available models for evaluating the laser damage resistance of exquisitely prepared optical components used in high power laser systems.

Effects of high repetition rate and beam size on hard tissue damage due to subpicosecond laser pulses

International Nuclear Information System (INIS)

Kim, Beop-Min; Feit, Michael D.; Rubenchik, Alexander M.; Joslin, Elizabeth J.; Eichler, Juergen; Stoller, Patrick C.; Da Silva, Luiz B.

2000-01-01

We report the effects of the repetition rate and the beam size on the threshold for ultrashort laser pulse induced damage in dentin. The observed results are explained as cumulative thermal effects. Our model is consistent with the experimental results and explains the dependence of the threshold on repetition rate, beam size, and exposure time. (c) 2000 American Institute of Physics

Time-resolved measurements with intense ultrashort laser pulses: a 'molecular movie' in real time

International Nuclear Information System (INIS)

Rudenko, A; Ergler, Th; Feuerstein, B; Zrost, K; Schroeter, C D; Moshammer, R; Ullrich, J

2007-01-01

We report on the high-resolution multidimensional real-time mapping of H 2 + and D 2 + nuclear wave packets performed employing time-resolved three-dimensional Coulomb explosion imaging with intense laser pulses. Exploiting a combination of a 'reaction microscope' spectrometer and a pump-probe setup with two intense 6-7 fs laser pulses, we simultaneously visualize both vibrational and rotational motion of the molecule, and obtain a sequence of snapshots of the squared ro-vibrational wave function with time-step resolution of ∼ 0.3 fs, allowing us to reconstruct a real-time movie of the ultrafast molecular motion. We observe fast dephasing, or 'collapse' of the vibrational wave packet and its subsequent revival, as well as signatures of rotational excitation. For D 2 + we resolve also the fractional revivals resulting from the interference between the counter-propagating parts of the wave packet

Determination of ablation threshold for composite resins and amalgam irradiated with femtosecond laser pulses

International Nuclear Information System (INIS)

Freitas, A Z; Samad, R E; Zezell, D M; Vieira Jr, N D; Freschi, L R; Gouw-Soares, S C

2010-01-01

The use of laser for caries removal and cavity preparation is already a reality in the dental clinic. The objective of the present study was to consider the viability of ultrashort laser pulses for restorative material selective removal, by determining the ablation threshold fluence for composite resins and amalgam irradiated with femtosecond laser pulses. Lasers pulses centered at 830 nm with 50 fs of duration and 1 kHz of repetition rate, with energies in the range of 300 to 770 μJ were used to irradiate the samples. The samples were irradiated using two different geometrical methods for ablation threshold fluence determinations and the volume ablation was measured by optical coherence tomography. The shape of the ablated surfaces were analyzed by optical microscopy and scanning electron microscopy. The determined ablation threshold fluence is 0.35 J/cm 2 for the composite resins Z-100 and Z-350, and 0.25 J/cm 2 for the amalgam. These values are half of the value for enamel in this temporal regime. Thermal damages were not observed in the samples. Using the OCT technique (optical coherence tomography) was possible to determine the ablated volume and the total mass removed

All-Fiber, Directly Chirped Laser Source for Chirped-Pulse-Amplification

Science.gov (United States)

Xin, Ran

Chirped-pulse-amplification (CPA) technology is widely used to produce ultra-short optical pulses (sub picosecond to femtoseconds) with high pulse energy. A chirped pulse laser source with flexible dispersion control is highly desirable as a CPA seed. This thesis presents an all-fiber, directly chirped laser source (DCLS) that produces nanosecond, linearly-chirped laser pulses at 1053 nm for seeding high energy CPA systems. DCLS produces a frequency chirp on an optical pulse through direct temporal phase modulation. DCLS provides programmable control for the temporal phase of the pulse, high pulse energy and diffraction-limited beam performance, which are beneficial for CPA systems. The DCLS concept is first described. Its key enabling technologies are identified and their experimental demonstration is presented. These include high-precision temporal phase control using an arbitrary waveform generator, multi-pass phase modulation to achieve high modulation depth, regenerative amplification in a fiber ring cavity and a negative feedback system that controls the amplifier cavity dynamics. A few technical challenges that arise from the multi-pass architecture are described and their solutions are presented, such as polarization management and gain-spectrum engineering in the DCLS fiber cavity. A DCLS has been built and its integration into a high energy OPCPA system is demonstrated. DCLS produces a 1-ns chirped pulse with a 3-nm bandwidth. The temporal phase and group delay dispersion on the DCLS output pulse is measured using temporal interferometry. The measured temporal phase has an ˜1000 rad amplitude and is close to a quadratic shape. The chirped pulse is amplified from 0.9 nJ to 76 mJ in an OPCPA system. The amplified pulse is compressed to close to its Fourier transform limit, producing an intensity autocorrelation trace with a 1.5-ps width. Direct compressed-pulse duration control by adjusting the phase modulation drive amplitude is demonstrated. Limitation

Soft x-ray generation in gases with an ultrashort pulse laser

Energy Technology Data Exchange (ETDEWEB)

Ditmire, Todd Raymond [Univ. of California, Davis, CA (United States)

1996-01-08

An experimental investigation of soft x-ray production resulting from the interaction of intense near infra-red laser radiation with gases is presented in this thesis. Specifically, soft x-ray generation through high order harmonic generation or exploiting intense inverse bremsstrahlung heating is examined. Most of these studies are conducted with femtosecond, terawatt class Cr:LiSrAlF₆ (LiSAF) laser, though results derived from studies with other laser systems are presented as well. The majority of this work is devoted to experimental investigations, however, theoretical and computational models are developed to interpret the data. These studies are motivated by the possibility of utilizing the physics of intense laser/matter interactions as a potential compact source of bright x-rays. Consequently, the thrust of many of the experiments conducted is aimed at characterizing the x-rays produced for possible use in applications. In general, the studies of this manuscript fall into three categories. First, a unique 130 fs, 8 TW laser that is based on chirped pulse amplification, is described, and its performance is evaluated. The generation of x-rays through high order harmonics is then discussed with emphasis on characterizing and optimizing harmonic generation. Finally, the generation of strong, incoherent x-ray radiation by the intense irradiation of large (>1,000 atom) clusters in gas jets, is explored. The physics of laser energy absorption by clusters illuminated with intensities of 10¹⁵ to 10¹⁷ W/cm² is considered in detail. X-ray spectroscopy of the hot plasmas that result from the irradiation of the clusters is conducted, and energy transport and kinetics issues in these plasmas are discussed.

Modification of transparent materials with ultrashort laser pulses: what is energetically and mechanically meaningful?

Czech Academy of Sciences Publication Activity Database

Bulgakova, Nadezhda M.; Zhukov, V.P.; Sonina, S.V.; Meshcheryakov, Y.P.

2015-01-01

Roč. 118, č. 23 (2015), 1-17, č. článku 233108. ISSN 0021-8979 R&D Projects: GA MŠk ED2.1.00/01.0027 Grant - others:HILASE(XE) CZ.1.05/2.1.00/01.0027 Institutional support: RVO:68378271 Keywords : bulk fused-silica * femtosecond-laser * wave-guides * structural modifications * induced nanogratings * repetition rate * amorphous sio2 * light-pulses * glass Subject RIV: BH - Optics, Masers, Lasers Impact factor: 2.101, year: 2015

Fs–ns double-pulse Laser Induced Breakdown Spectroscopy of copper-based-alloys: Generation and elemental analysis of nanoparticles

Energy Technology Data Exchange (ETDEWEB)

Guarnaccio, A.; Parisi, G.P.; Mollica, D. [CNR-ISM, U.O.S. Tito Scalo, Zona Industriale, 85050 Tito Scalo, PZ (Italy); De Bonis, A. [CNR-ISM, U.O.S. Tito Scalo, Zona Industriale, 85050 Tito Scalo, PZ (Italy); Dipartimento di Scienze, Università degli Studi della Basilicata, Via dell' Ateneo Lucano 10, 85100 Potenza (Italy); Teghil, R. [Dipartimento di Scienze, Università degli Studi della Basilicata, Via dell' Ateneo Lucano 10, 85100 Potenza (Italy); Santagata, A. [CNR-ISM, U.O.S. Tito Scalo, Zona Industriale, 85050 Tito Scalo, PZ (Italy)

2014-11-01

Evolution of nanoparticles ejected during ultra-short (250 fs) laser ablation of certified copper alloys and relative calibration plots of a fs–ns double-pulse Laser Induced Breakdown Spectroscopy orthogonal configuration is presented. All work was performed in air at atmospheric pressure using certified copper-based-alloy samples irradiated by a fs laser beam and followed by a delayed perpendicular ns laser pulse. In order to evaluate possible compositional changes of the fs induced nanoparticles, it was necessary to consider, for all samples used, comparable features of the detected species. With this purpose the induced nanoparticles black-body-like emission evolution and their relative temperature decay have been studied. These data were exploited for defining the distance between the target surface and the successive ns laser beam to be used. The consequent calibration plots of minor constituents (i.e. Sn, Pb and Zn) of the certified copper-based-alloy samples have been reported by taking into account self-absorption effects. The resulting linear regression coefficients suggest that the method used, for monitoring and ruling the fs laser induced nanoparticles, could provide a valuable approach for establishing the occurrence of potential compositional changes of the detected species. All experimental data reveal that the fs laser induced nanoparticles can be used for providing a coherent composition of the starting target. In the meantime, the fs–ns double-pulse Laser Induced Breakdown Spectroscopy orthogonal configuration here used can be considered as an efficient technique for compositional determination of the nanoparticles ejected during ultra-short laser ablation processes. - Highlights: • Laser induced NP continuum black-body-like emission was used for T determination. • Invariable composition of generated NPs was assumed in the range of 20 μs. • Fs-ns DP-LIBS was employed for the compositional characterization of NPs. • NPs obtained by fs

ILIAS. Ion and laser beam interaction and application studies. Progress report no. 3 of the PHELIX theory group

Energy Technology Data Exchange (ETDEWEB)

Mulser, P. (ed.)

2008-04-15

The following topics are dealt with: The PHELIX laser-plasma facility, coupling of nuclear matter to intense photon fields, QED effects in strong laser fields, relativistic critical density increase in a linearly polarized laser beam, absorption of ultrashort laser pulses in strongly overdense targets, Coulomb focusing in electron-ion collisions in a strong laser field, quasiperiodic waves in relativistic plasmas, high-energy-density physics studied by intense particle beams, heavy ions in a high-power laser beam, Monte-Carlo study of electron dynamics in silicon during irradiation with an ultrashort VUV laser pulse. (HSI)

ILIAS. Ion and laser beam interaction and application studies. Progress report no. 3 of the PHELIX theory group

International Nuclear Information System (INIS)

Mulser, P.

2008-04-01

The following topics are dealt with: The PHELIX laser-plasma facility, coupling of nuclear matter to intense photon fields, QED effects in strong laser fields, relativistic critical density increase in a linearly polarized laser beam, absorption of ultrashort laser pulses in strongly overdense targets, Coulomb focusing in electron-ion collisions in a strong laser field, quasiperiodic waves in relativistic plasmas, high-energy-density physics studied by intense particle beams, heavy ions in a high-power laser beam, Monte-Carlo study of electron dynamics in silicon during irradiation with an ultrashort VUV laser pulse. (HSI)

Retrieving molecular structural information and tracking HNC/HCN isomerization process with high harmonic generation by ultrashort laser pulses

International Nuclear Information System (INIS)

Nguyen Ngoc Ty; Le Van Hoang; Vu Ngoc Tuoc; Le Anh Thu

2010-01-01

We investigate the possibility of applying the iterative method, suggested in our previous work, for HCN molecule and its HNC isomer. We found that the high-order harmonic generation (HHG) spectra are quite insensitive to the change of H-C (or H-N) bond length so that only the inter-nuclear C-N distance can be retrieved from the high-order harmonic spectra using ultrashort intense lasers. Furthermore, by analyzing the HHG spectra emitted by HCN during the chemical reaction path of isomerization we identify the intensity peaks nearby the stable, metastable and transition states. this finding can be useful for tracking the HNC/HNC isomerization process. (author)

Controlling semiconductor nanoparticle size distributions with tailored ultrashort pulses

International Nuclear Information System (INIS)

Hergenroeder, R; Miclea, M; Hommes, V

2006-01-01

The laser generation of size-controlled semiconductor nanoparticle formation under gas phase conditions is investigated. It is shown that the size distribution can be changed if picosecond pulse sequences of tailored ultra short laser pulses (<200 fs) are employed. By delivering the laser energy in small packages, a temporal energy flux control at the target surface is achieved, which results in the control of the thermodynamic pathway the material takes. The concept is tested with silicon and germanium, both materials with a predictable response to double pulse sequences, which allows deduction of the materials' response to complicated pulse sequences. An automatic, adaptive learning algorithm was employed to demonstrate a future strategy that enables the definition of more complex optimization targets such as particle size on materials less predictable than semiconductors

Selective ablation of a titanium nitride film on tungsten carbide substrate using ultrashort laser pulses; Ablação seletiva de um filme de nitreto de titânio em substrato de carboneto de tungstênio utilizando laser de pulsos ultracurtos

Energy Technology Data Exchange (ETDEWEB)

Oliveira, Eduardo Spinelli

2017-07-01

Surface coatings are applied to many cutting tools in the metallurgical industry in order to improve cutting efficiency and extend its useful life. In this work, tests were performed to remove the coating of titanium aluminum nitride (TiAlN) on tungsten carbide (WC-Co) pellets, using an ultrashort laser pulses beam. After determination of the damage thresholds of the film and the substrate, were ablated on the surface of the coating lines using two ablation conditions, it was initially operated on the low fluence regime for the film, and later on the low fluence regime of the substrate, far below the threshold of the film, applying high overlapping pulses. A laser induced breakdown spectroscopy (LIBS) system was set up to monitor the materials present in the plasma generated by the laser, but the system did not present sufficient sensitivity to read the low intensity of the plasma generated in the process and was not used. After the analysis of the traces by electron microscopy, optical profilometer and X-ray fluorescence spectroscopy, it was not possible to determine a safe process to carry out the selective removal of the film in question, however, due to the data obtained and observations of the results in some traces, new possibilities were raised, opening the discussion for future work. (author)

Recent progress on laser acceleration research

International Nuclear Information System (INIS)

Nakajima, Kazuhisa; Dewa, Hideki; Hosokai, Tomonao; Kanazawa, Shuhei; Kando, Masaki; Kondoh, Shuji; Kotaki, Hideyuki

2000-01-01

Recently there has been a tremendous experimental progress in ultrahigh field particle acceleration driven by ultraintense laser pulses in plasmas. A design of the laser wakefield accelerators aiming at GeV energy gains is discussed by presenting our recent progress on the laser wakefield acceleration experiments, the developments of high quality electron beam injectors and the capillary plasma waveguide for optical guiding of ultrashort intense laser pulses. (author)

Anterior capsulotomy with an ultrashort-pulse laser.

Science.gov (United States)

Tackman, Ramon Naranjo; Kuri, Jorge Villar; Nichamin, Louis D Skip; Edwards, Keith

2011-05-01

To assess the precision of laser anterior capsulotomy compared with that of manual continuous curvilinear capsulorhexis (CCC). Asociación Para Evitar La Ceguera en México IAP, Hospital Dr. Luis Sánchez Bulnes, Mexico City, Mexico. Nonrandomized single-center clinical trial. In patients presenting for cataract surgery, the LensAR Laser System was used to create a laser anterior capsulotomy of the surgeon's desired size. Capsule buttons were retrieved and measured and then compared with buttons retrieved from eyes having a manually torn CCC. Deviation from the intended diameter and the regularity of shape were assessed. When removing the capsule buttons at the start of surgery, the surgeon rated the ease of removal on a scale of 1 to 10 (1 = required manual capsulorhexis around the whole diameter; 10 = button free floating or required no manual detachment from remaining capsule during removal). The mean deviation from the intended diameter was 0.16 mm ± 0.17 (SD) for laser anterior capsulotomy and 0.42 ± 0.54 mm for CCC (P=.03). The mean absolute deviation from the intended diameter was 0.20 ± 0.12 mm and 0.49 ± 0.47 mm, respectively (P=.003). The mean of the average squared residuals was 0.01 ± 0.03 and 0.02 ± 0.04, respectively (P=.09). The median rating of the ease of removal was 9 (range 5 to 10). Laser anterior capsulotomy created a more precise capsule opening than CCC, and the buttons created by the laser procedure were easy to remove at the beginning of cataract surgery. Copyright © 2011 ASCRS and ESCRS. Published by Elsevier Inc. All rights reserved.

A broadly tunable autocorrelator for ultra-short, ultra-high power infrared optical pulses

Energy Technology Data Exchange (ETDEWEB)

Szarmes, E.B.; Madey, J.M.J. [Duke Univ., Durham, NC (United States)

1995-12-31

We describe the design of a crossed-beam, optical autocorrelator that uses an uncoated, birefringent beamsplitter to split a linearly polarized incident pulse into two orthogonally polarized pulses, and a Type II, SHG crystal to generate the intensity autocorrelation function. The uncoated beamsplitter accommodates extremely broad tunability while precluding any temporal distortion of ultrashort optical pulses at the dielectric interface, and the specific design provides efficient operation between 1 {mu}m and 4 {mu}m. Furthermore, the use of Type II SHG completely eliminates any single-beam doubling, so the autocorrelator can be operated at very shallow crossed-beam angles without generating a background pedestal. The autocorrelator has been constructed and installed in the Mark III laboratory at Duke University as a broadband diagnostic for ongoing compression experiments on the chirped-pulse FEL.

Dynamics of laser ablation at the early stage during and after ultrashort pulse

International Nuclear Information System (INIS)

Ilnitsky, D K; Zhakhovsky, V V; Migdal, K P; Inogamov, N A; Khokhlov, V A; Petrov, Yu V

2016-01-01

Study of material flow in two-temperature states is needed for a fundamental understanding the physics of femtosecond laser ablation. To explore phenomena at a very early stage of laser action on a metallic target our in-house two-temperature hydrodynamics code is used here. The early stage covers duration of laser pulse with next first few picoseconds. We draw attention to the difference in behavior at this stage between the cases: (i) of an ultrathin film (thickness of order of skin depth d skin or less), (ii) thin films (thickness of a film is 4-7 of d skin for gold), and (iii) bulk targets (more than 10 d skin for gold). We demonstrate that these differences follow from a competition among conductive cooling of laser excited electrons in a skin layer, electron-ion coupling, and hydrodynamics of unloading caused by excess of pressure of excited free electrons. Conductive cooling of the skin needs a heat sink, which is performed by the cold material outside the skin. Such sink is unavailable in the ultrathin films. (paper)

TruMicro Series 2000 sub-400 fs class industrial fiber lasers: adjustment of laser parameters to process requirements

Science.gov (United States)

Kanal, Florian; Kahmann, Max; Tan, Chuong; Diekamp, Holger; Jansen, Florian; Scelle, Raphael; Budnicki, Aleksander; Sutter, Dirk

2017-02-01

The matchless properties of ultrashort laser pulses, such as the enabling of cold processing and non-linear absorption, pave the way to numerous novel applications. Ultrafast lasers arrived in the last decade at a level of reliability suitable for the industrial environment.1 Within the next years many industrial manufacturing processes in several markets will be replaced by laser-based processes due to their well-known benefits: These are non-contact wear-free processing, higher process accuracy or an increase of processing speed and often improved economic efficiency compared to conventional processes. Furthermore, new processes will arise with novel sources, addressing previously unsolved challenges. One technical requirement for these exciting new applications will be to optimize the large number of available parameters to the requirements of the application. In this work we present an ultrafast laser system distinguished by its capability to combine high flexibility and real time process-inherent adjustments of the parameters with industry-ready reliability. This industry-ready reliability is ensured by a long experience in designing and building ultrashort-pulse lasers in combination with rigorous optimization of the mechanical construction, optical components and the entire laser head for continuous performance. By introducing a new generation of mechanical design in the last few years, TRUMPF enabled its ultrashort-laser platforms to fulfill the very demanding requirements for passively coupling high-energy single-mode radiation into a hollow-core transport fiber. The laser architecture presented here is based on the all fiber MOPA (master oscillator power amplifier) CPA (chirped pulse amplification) technology. The pulses are generated in a high repetition rate mode-locked fiber oscillator also enabling flexible pulse bursts (groups of multiple pulses) with 20 ns intra-burst pulse separation. An external acousto-optic modulator (XAOM) enables linearization

Time-resolved investigations of the fragmentation dynamic of H2 (D2) in and with ultra-short laser pulses

International Nuclear Information System (INIS)

Ergler, T.

2006-01-01

In course of this work pump-probe experiments aimed to study ultrafast nuclear motion in H 2 (D 2 ) fragmentation by intense 6-25 fs laser pulses have been carried out. In order to perform time-resolved measurements, a Mach-Zehnder interferometer providing two identical synchronized laser pulses with the time-delay variable from 0 to 3000 fs with 300 as accuracy and long-term stability has been built. The laser pulses at the intensities of up to 10 15 W/cm 2 were focused onto a H 2 (D 2 ) molecular beam leading to the ionization or dissociation of the molecules, and the momenta of all charged reactions fragments were measured with a reaction microscope. With 6-7 fs pulses it was possible to probe the time evolution of the bound H + 2 (D + 2 ) nuclear wave packet created by the first (pump) laser pulse, fragmenting the molecule with the second (probe) pulse. A fast delocalization, or ''collapse'', and subsequent ''revival'' of the vibrational wave packet have been observed. In addition, the signatures of the ground state vibrational excitation in neutral D 2 molecule have been found, and the dominance of a new, purely quantum mechanical wave packet preparation mechanism (the so-called ''Lochfrass'') has been proved. In the experiments with 25 fs pulses the theoretically predicted enhancement of the ionization probability for the dissociating H + 2 molecular ion at large internuclear distances has been detected for the first time. (orig.)

Studies on widely tunable ultra-short laser pulses using energy transfer distributed feedback dye laser

International Nuclear Information System (INIS)

Ahamed, M.B.; Ramalingam, A.; Palanisamy, P.K.

2003-01-01

This paper presents both theoretical and experimental study of the characteristics of Nd: YAG laser pumped energy transfer distributed feedback dye laser (ETDFDL). Using theoretical model proposed, the behavior of ETDFDL such as the characteristics of donor DFDL, the acceptor DFDL, the dependence of their pulse width and output power on donor-acceptor concentrations and pump power are studied for dye mixture Rhodamine 6G and Cresyl Violet in detail. Experimentally using prism-dye cell configuration, the ETDFDL output is obtained and the output energy of DFDL is measured at the emission peaks of donor and acceptor dyes for different pump powers and donor-acceptor concentrations. In addition, the DFDL linewidth measurement has been carried out at the lasing wavelengths of the donor and acceptor dyes using Fabry-Perot etalon and the tunability of DFDL is measured to be in the wavelength range of 545-680 nm

Laser-Bioplasma Interaction: The Blood Type Transmutation Induced by Multiple Ultrashort Wavelength Laser Beams

Science.gov (United States)

Stefan, V. Alexander

2015-11-01

The interaction of ultrashort wavelength multi laser beams with the flowing blood thin films leads to the transmutation of the blood types A, B, and AB into O type. This is a novel mechanism of importance for the transfusion medicine. Laser radiation is in resonance with the eigen-frequency modes of the antigen proteins and forces the proteins to parametrically oscillate until they get kicked out from the surface. The stripping away of antigens is done by the scanning-multiple-lasers of a high repetition rate in the blue-purple frequency domain. The guiding-lasers are in the red-green frequency domain. The laser force, (parametric interaction with the antigen eigen-oscillation), upon the antigen protein molecule must exceed its weight. The scanning laser beam is partially reflected as long as the antigen(s) is not eliminated. The process of the protein detachment can last a few minutes. Supported by Nikola Tesla Labs., Stefan University.

A proposed laser wakefield acceleration experiment

International Nuclear Information System (INIS)

Ebrahim, N.A.

1995-05-01

In this report we discuss the basic concepts of a laser wakefield experiment using an ultrashort laser pulse. In particular, we obtain some heuristic estimates of experimental parameters relevant to an experiment to test the laser wakefield acceleration concept. (author). 8 refs., 2 tabs

Plasma heating by ultrashort laser pulse in the regime of anomalous skin-effect

International Nuclear Information System (INIS)

Gamaly, E.G.; Kiselev, A.E.; Tikhonchuk, V.T.

1991-01-01

The problem of interaction of short laser pulse (light frequency ω 0 pulse duration, τ s /V Ti ; 1 s , skin depth, V Ti , ion velocity) with dense (ω 0 much-lt ω pe ) semi-infinite plasm was solved. The authors formulated the self-consistent problem of obtaining the electron distribution function and space dependence of electric field in skin layer, and solved the problem for the case of absence of the energy losses from the skin layer. The authors found self-similar nonstationary electron distribution function and space dependence of electric field in this case, and basing on these solutions, have calculated mean electron energy, absorption coefficient, bremsstrahlung radiation, time dependent skin depth. This paper discusses the limitations of our theory

Single-shot spectro-temporal characterization of XUV pulses from a seeded free-electron laser

Science.gov (United States)

de Ninno, Giovanni; Gauthier, David; Mahieu, Benoît; Ribič, Primož Rebernik; Allaria, Enrico; Cinquegrana, Paolo; Danailov, Miltcho Bojanov; Demidovich, Alexander; Ferrari, Eugenio; Giannessi, Luca; Penco, Giuseppe; Sigalotti, Paolo; Stupar, Matija

2015-08-01

Intense ultrashort X-ray pulses produced by modern free-electron lasers (FELs) allow one to probe biological systems, inorganic materials and molecular reaction dynamics with nanoscale spatial and femtoscale temporal resolution. These experiments require the knowledge, and possibly the control, of the spectro-temporal content of individual pulses. FELs relying on seeding have the potential to produce spatially and temporally fully coherent pulses. Here we propose and implement an interferometric method, which allows us to carry out the first complete single-shot spectro-temporal characterization of the pulses, generated by an FEL in the extreme ultraviolet spectral range. Moreover, we provide the first direct evidence of the temporal coherence of a seeded FEL working in the extreme ultraviolet spectral range and show the way to control the light generation process to produce Fourier-limited pulses. Experiments are carried out at the FERMI FEL in Trieste.

Comparison of retina damage thresholds simulating the femtosecond-laser in situ keratomileusis (fs-LASIK) process with two laser systems in the CW- and fs-regime

Science.gov (United States)

Sander, M.; Minet, O.; Zabarylo, U.; Müller, M.; Tetz, M. R.

2012-04-01

The femtosecond-laser in situ keratomileusis procedure affords the opportunity to correct ametropia by cutting transparent corneal tissue with ultra-short laser pulses. Thereby the tissue cut is generated by a laser-induced optical breakdown in the cornea with ultra-short laser pulses in the near-infrared range. Compared to standard procedures such as photorefractive keratectomy and laser in-situ keratomileusis with the excimer laser, where the risk potential for the eye is low due to the complete absorption of ultraviolet irradiation from corneal tissue, only a certain amount of the pulse energy is deposited in the cornea during the fs-LASIK process. The remaining energy propagates through the eye and interacts with the retina and the strong absorbing tissue layers behind. The objective of the presented study was to determine and compare the retina damage thresholds during the fs-LASIK process simulated with two various laser systems in the CW- and fs-regime.

A plasma microlens for ultrashort high power lasers

Science.gov (United States)

Katzir, Yiftach; Eisenmann, Shmuel; Ferber, Yair; Zigler, Arie; Hubbard, Richard F.

2009-07-01

We present a technique for generation of miniature plasma lens system that can be used for focusing and collimating a high intensity femtosecond laser pulse. The plasma lens was created by a nanosecond laser, which ablated a capillary entrance. The spatial configuration of the ablated plasma focused a high intensity femtosecond laser pulse. This configuration offers versatility in the plasma lens small f-number for extremely tight focusing of high power lasers with no damage threshold restrictions of regular optical components.

A plasma microlens for ultrashort high power lasers

International Nuclear Information System (INIS)

Katzir, Yiftach; Eisenmann, Shmuel; Ferber, Yair; Zigler, Arie; Hubbard, Richard F.

2009-01-01

We present a technique for generation of miniature plasma lens system that can be used for focusing and collimating a high intensity femtosecond laser pulse. The plasma lens was created by a nanosecond laser, which ablated a capillary entrance. The spatial configuration of the ablated plasma focused a high intensity femtosecond laser pulse. This configuration offers versatility in the plasma lens small f-number for extremely tight focusing of high power lasers with no damage threshold restrictions of regular optical components.

Isolated sub-100-as pulse generation via controlling electron dynamics

International Nuclear Information System (INIS)

Lan Pengfei; Lu Peixiang; Cao Wei; Li Yuhua; Wang Xinlin

2007-01-01

A method to coherently control electron dynamics is proposed using a few-cycle laser pulse in combination with a controlling field. It is shown that this method not only broadens the attosecond pulse bandwidth, but also reduces the chirp; thus an isolated 80-as pulse is straightforwardly obtained, and even shorter pulses are achievable by increasing the intensity of the controlling field. Such ultrashort pulses allow one to investigate ultrafast electronic processes. In addition, the few-cycle synthesized pulse is expected to be useful for manipulating a wide range of laser-atom interactions

Supersonic Ionization Wave Driven by Radiation Transport in a Short-Pulse Laser-Produced Plasma

International Nuclear Information System (INIS)

Ditmire, T.; Gumbrell, E.T.; Smith, R.A.; Mountford, L.; Hutchinson, M.H.

1996-01-01

Through the use of an ultrashort (2ps) optical probe, we have time resolved the propagation of an ionization wave into solid fused silica. This ionization wave results when a plasma is created by the intense irradiation of a solid target with a 2ps laser pulse. We find that the velocity of the ionization wave is consistent with radiation driven thermal transport, exceeding the velocity expected from simple electron thermal conduction by nearly an order of magnitude. copyright 1996 The American Physical Society

Simple formula for photoprocesses in ultrashort electromagnetic field

International Nuclear Information System (INIS)

Astapenko, V.A.

2010-01-01

Within the framework of the perturbation theory, a simple formula for the probability of a photoprocess for the whole time of action of an ultrashort electromagnetic pulse has been derived, when the concept of spectral intensity of radiation and probability per unit time is inapplicable. In the obtained formula the total probability is expressed in terms of the cross-section of a photoprocess in a monochromatic field and the Fourier transform of electric field strength. The advanced approach is applied for the analysis of photoabsorption of an atom and a metal nanosphere under the action of a subcycle laser pulse with a changeable value of the carrier-envelope phase. The expressions for probability and energy of photoabsorption in the limit of a zero pulse duration have been obtained.

Ultrafast population transfer in a Λ-configuration level system driven by few-cycle laser pulses

International Nuclear Information System (INIS)

Zhang Wen-Jing; Xie Xiao-Tao; Jin Lu-Ling; Bai Jin-Tao

2013-01-01

The feasibility of population transfer from a populated level via an intermediate state to the target level driven by few-cycle pulses is theoretically discussed. The processes of on- or far-resonance stimulated Raman scattering with sequential or simultaneous ultrashort pulses are investigated respectively. We find that the ultrashort pulses with about two optical cycles can be used to realize the population operation. This suggests that the population transfer can be completed in the femtosecond time scale. At the same time, our simulation shows that the signal of the carrier-envelope-phase-dependent effect can be enlarged due to quantum interference in some conditions. Our theoretic study may promote the research on the coherent control via ultrashort pulses in the related fields

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)

Breaking time-resolution limits in pulse radiolysis

International Nuclear Information System (INIS)

Yang Jinfeng; Kondoh, Takafumi; Norizawa, Kimihiro; Yoshida, Yoichi; Tagawa, Seiichi

2009-01-01

Pulse radiolysis, which is a time-resolved stroboscopic method based on ultrashort electron pulse and ultrashort analyzing light, is widely used for the study of the chemical kinetics and radiation primary processes or reactions. Although it has become possible to use femtosecond-pulse electron beam and femtosecond laser light in pulse radiolysis, the resolution is limited by the difference in group velocities of the electrons and the light in sample. In this contribution, we introduce a concept of equivalent velocity spectroscopy (EVS) into pulse radiolysis and demonstrate the methodology experimentally. In EVS, both the electron and the analyzing light pulses precisely overlap at every point in the sample and throughout the propagation time by rotating the electron pulse. The advance allows us to overcome the resolution degradation due to the different group velocity. We also present a method for measuring the rotated angle of the electron pulse and a technique for rotating the electron pulse with a deflecting cavity.

Femtosecond laser excitation of dielectric materials

DEFF Research Database (Denmark)

Wædegaard, Kristian Juncher; Balling, Peter; Frislev, Martin Thomas

2012-01-01

We report an approach to modeling the interaction between ultrashort laser pulses and dielectric materials. The model includes the excitation of carriers by the laser through strongfield excitation, collisional excitation, and absorption in the plasma consisting of conduction-band electrons formed...

Ultrashort Pulsed Laser Ablation of Magnesium Diboride: Plasma Characterization and Thin Films Deposition

Directory of Open Access Journals (Sweden)

Angela De Bonis

2015-01-01

Full Text Available A MgB2 target has been ablated by Nd:glass laser with a pulse duration of 250 fs. The plasma produced by the laser-target interaction, showing two temporal separated emissions, has been characterized by time and space resolved optical emission spectroscopy and ICCD fast imaging. The films, deposited on silicon substrates and formed by the coalescence of particles with nanometric size, have been analyzed by scanning electron microscopy, atomic force microscopy, X-ray photoelectron spectroscopy, micro-Raman spectroscopy, and X-ray diffraction. The first steps of the films growth have been studied by Transmission Electron Microscopy. The films deposition has been studied by varying the substrate temperature from 25 to 500°C and the best results have been obtained at room temperature.

Coherent control of atoms and diatomic molecules with shaped ultrashort pulses

International Nuclear Information System (INIS)

Degert, J.

2002-12-01

This thesis deals with the theoretical and experimental study of coherent control of atomic and molecular systems with shaped pulses. At first, we present several experiments of control of coherent transients in rubidium. These transients appear when a two-level system is excited by a perturbative chirped pulse, and are characterized by oscillations in the excited state population. For a strong chirp, we show that a phase step in the spectrum modifies the phase of the oscillations. Then, by direct analogy with Fresnel zone lens, we conceive a chirped pulse with a highly modulated amplitude, allowing to suppress destructive contributions to the population transfer. In a second set of experiments, we focus on quantum path interferences in two-photon transitions excited by linearly chirped pulses. Owing to the broad bandwidth of ultrashort pulses, sequential and direct excitation paths contribute to the excited state population. Oscillations resulting from interferences between these two paths are observed in atomic sodium. Moreover, we show that they are observable whatever the sign of chirp. Theoretically, we study the control of the predissociation of a benchmark diatomic molecule: NaI. Predissociation leads to matter wave interferences in the fragments distribution. First, we show that a suitably chosen probe pulse allows the observation of theses interferences. Next, using a sequence of control pulse inducing electronic transition, we demonstrate the possibility to manipulate fragment energy distribution. (author)

New theoretical approaches to atomic and molecular dynamics triggered by ultrashort light pulses on the atto- to picosecond time scale

International Nuclear Information System (INIS)

Pabst, Stefan Ulf

2013-04-01

diffraction pattern, information about the molecular structure can be gained. This is illustrated with the example of laser-aligned naphthalene molecules (C 10 H 8 ). Furthermore, I demonstrate that the quality of the molecular alignment is essential for the reconstruction of the molecular structure. In the second part of this work, the ionization dynamics of atoms is studied. The characteristic time scale lies, here, in the attosecond and the few-femtosecond regime. Although a one-particle picture has been successfully applied to many ionization processes, important many-body effects do constantly occur. Based on a time-dependent configurationinteraction singles (TDCIS) approach, I study the temporal behavior of these many-body effects. During the photoionization of atomic xenon, unexpected correlation effects between the ionized electron and the ion occur. This electron-ion entanglement results in a reduced coherence within the ion. Populations and coherences of the ionic states are probed with attosecond precision using transient absorption spectroscopy. Even the subcycle ionization dynamics can be studied with this technique. Here, field-driven dressing effects between the ion and the freed electron appear, which I investigate on atomic krypton. Interactions between the ion and the electron, which modify the ionic states, occur also in high-harmonic generation (HHG). They are visible in the HHG spectrum as my studies of argon and xenon show. All these examples demonstrate on the one side, ultrashort pulses can be used to initiate complex electronic, atomic, and molecular motions. On the other side, it is also possible to probe and to control these dynamical processes with ultrashort pulses.

New theoretical approaches to atomic and molecular dynamics triggered by ultrashort light pulses on the atto- to picosecond time scale

Energy Technology Data Exchange (ETDEWEB)

Pabst, Stefan Ulf

2013-04-15

diffraction pattern, information about the molecular structure can be gained. This is illustrated with the example of laser-aligned naphthalene molecules (C{sub 10}H{sub 8}). Furthermore, I demonstrate that the quality of the molecular alignment is essential for the reconstruction of the molecular structure. In the second part of this work, the ionization dynamics of atoms is studied. The characteristic time scale lies, here, in the attosecond and the few-femtosecond regime. Although a one-particle picture has been successfully applied to many ionization processes, important many-body effects do constantly occur. Based on a time-dependent configurationinteraction singles (TDCIS) approach, I study the temporal behavior of these many-body effects. During the photoionization of atomic xenon, unexpected correlation effects between the ionized electron and the ion occur. This electron-ion entanglement results in a reduced coherence within the ion. Populations and coherences of the ionic states are probed with attosecond precision using transient absorption spectroscopy. Even the subcycle ionization dynamics can be studied with this technique. Here, field-driven dressing effects between the ion and the freed electron appear, which I investigate on atomic krypton. Interactions between the ion and the electron, which modify the ionic states, occur also in high-harmonic generation (HHG). They are visible in the HHG spectrum as my studies of argon and xenon show. All these examples demonstrate on the one side, ultrashort pulses can be used to initiate complex electronic, atomic, and molecular motions. On the other side, it is also possible to probe and to control these dynamical processes with ultrashort pulses.

Complex {PT}-symmetric extensions of the nonlinear ultra-short light pulse model

Science.gov (United States)

Yan, Zhenya

2012-11-01

The short pulse equation u_{xt}=u+\\frac{1}{2}(u^2u_x)_x is PT symmetric, which arises in nonlinear optics for the ultra-short pulse case. We present a family of new complex PT-symmetric extensions of the short pulse equation, i[(iu_x)^{\\sigma }]_t=au+bu^m+ic[u^n(iu_x)^{\\epsilon }]_x \\,\\, (\\sigma ,\\, \\epsilon ,\\,a,\\,b,\\,c,\\,m,\\,n \\in {R}), based on the complex PT-symmetric extension principle. Some properties of these equations with some chosen parameters are studied including the Hamiltonian structures and exact solutions such as solitary wave solutions, doubly periodic wave solutions and compacton solutions. Our results may be useful to understand complex PT-symmetric nonlinear physical models. This article is part of a special issue of Journal of Physics A: Mathematical and Theoretical devoted to ‘Quantum physics with non-Hermitian operators’.

Air-guided photonic-crystal-fiber pulse-compression delivery of multimegawatt femtosecond laser output for nonlinear-optical imaging and neurosurgery

Science.gov (United States)

Lanin, Aleksandr A.; Fedotov, Il'ya V.; Sidorov-Biryukov, Dmitrii A.; Doronina-Amitonova, Lyubov V.; Ivashkina, Olga I.; Zots, Marina A.; Sun, Chi-Kuang; Ömer Ilday, F.; Fedotov, Andrei B.; Anokhin, Konstantin V.; Zheltikov, Aleksei M.

2012-03-01

Large-core hollow photonic-crystal fibers (PCFs) are shown to enable a fiber-format air-guided delivery of ultrashort infrared laser pulses for neurosurgery and nonlinear-optical imaging. With an appropriate dispersion precompensation, an anomalously dispersive 15-μm-core hollow PCF compresses 510-fs, 1070-nm light pulses to a pulse width of about 110 fs, providing a peak power in excess of 5 MW. The compressed PCF output is employed to induce a local photodisruption of corpus callosum tissues in mouse brain and is used to generate the third harmonic in brain tissues, which is captured by the PCF and delivered to a detector through the PCF cladding.

Time resolved studies of H{sub 2}{sup +} dissociation with phase-stabilized laser pulses

Energy Technology Data Exchange (ETDEWEB)

Fischer, Bettina

2010-06-23

In the course of this thesis, experimental studies on the dissociation of H{sub 2}{sup +}(H{sub 2}{sup +}{yields}p+H) in ultrashort laser pulses with a stabilized carrier-envelope phase (CEP) were carried out. In single-pulse measurements, the ability to control the emission direction of low energetic protons, i.e. the localization of the bound electron at one of the nuclei after dissociation, by the CEP was demonstrated. The coincident detection of the emitted protons and electrons and the measurement of their three-dimensional momentum vectors with a reaction microscope allowed to clarify the localization mechanism. Further control was achieved by a pump-control scheme with two timedelayed CEP-stabilized laser pulses. Here the neutral H{sub 2} molecule was ionized in the first pulse and dissociation was induced by the second pulse. Electron localization was shown to depend on the properties of the bound nuclear wave packet in H{sub 2}{sup +} at the time the control pulse is applied, demonstrating the ability to use the shape and dynamics of the nuclear wave packet as control parameters. Wave packet simulations were performed reproducing qualitatively the experimental results of the single and the two-pulse measurements. For both control schemes, intuitive models are presented, which qualitatively explain the main features of the obtained results. (orig.)

Layer-by-layer modification of thin-film metal-semiconductor multilayers with ultrashort laser pulses

Science.gov (United States)

Romashevskiy, S. A.; Tsygankov, P. A.; Ashitkov, S. I.; Agranat, M. B.

2018-05-01

The surface modifications in a multilayer thin-film structure (50-nm alternating layers of Si and Al) induced by a single Gaussian-shaped femtosecond laser pulse (350 fs, 1028 nm) in the air are investigated by means of atomic-force microscopy (AFM), scanning electron microscopy (SEM), and optical microscopy (OM). Depending on the laser fluence, various modifications of nanometer-scale metal and semiconductor layers, including localized formation of silicon/aluminum nanofoams and layer-by-layer removal, are found. While the nanofoams with cell sizes in the range of tens to hundreds of nanometers are produced only in the two top layers, layer-by-layer removal is observed for the four top layers under single pulse irradiation. The 50-nm films of the multilayer structure are found to be separated at their interfaces, resulting in a selective removal of several top layers (up to 4) in the form of step-like (concentric) craters. The observed phenomenon is associated with a thermo-mechanical ablation mechanism that results in splitting off at film-film interface, where the adhesion force is less than the bulk strength of the used materials, revealing linear dependence of threshold fluences on the film thickness.

Magnetic resonance imaging of the normal pituitary gland using ultrashort TE (UTE) pulse sequences (REV 1.0)

International Nuclear Information System (INIS)

Portman, Olivia; Flemming, Stephen; Cox, Jeremy P.D.; Johnston, Desmond G.; Bydder, Graeme M.

2008-01-01

The purpose of this study was to examine the normal pituitary gland in male subjects with ultrashort echo time (TE) pulse sequences, describe its appearance and measure its signal intensity before and after contrast enhancement. Eleven male volunteers (mean age 57.1 years; range 36-81 years) were examined with a fat-suppressed ultrashort TE (= 0.08 ms) pulse sequence. The studies were repeated after the administration of intravenous gadodiamide. The MR scans were examined for gland morphology and signal intensity before and after enhancement. Endocrinological evaluation included baseline pituitary function tests and a glucagon stimulatory test to assess pituitary cortisol and growth hormone reserve. High signal intensity was observed in the anterior pituitary relative to the brain in nine of the 11 subjects. These regions involved the whole of the anterior pituitary in three subjects, were localised to one side in two examples and were seen inferiorly in three subjects. Signal intensities relative to the brain increased with age, with a peak around the sixth or seventh decade and decreasing thereafter. Overall, the pituitary function tests were considered to be within normal limits and did not correlate with pituitary gland signal intensity. The anterior pituitary shows increased signal intensity in normal subjects when examined with T 1 -weighted ultrashort TE pulse sequences. The cause of this increased intensity is unknown, but fibrosis and iron deposition are possible candidates. The variation in signal intensity with age followed the temporal pattern of iron content observed at post mortem. No relationship with endocrine status was observed. (orig.)

Magnetic resonance imaging of the normal pituitary gland using ultrashort TE (UTE) pulse sequences (REV 1.0)

Energy Technology Data Exchange (ETDEWEB)

Portman, Olivia; Flemming, Stephen; Cox, Jeremy P.D.; Johnston, Desmond G. [Imperial College Faculty of Medicine, St Mary' s Hospital, Endocrinology and Metabolic Medicine, London (United Kingdom); Bydder, Graeme M. [University of California, San Diego, Department of Radiology, San Diego, CA (United States)

2008-03-15

The purpose of this study was to examine the normal pituitary gland in male subjects with ultrashort echo time (TE) pulse sequences, describe its appearance and measure its signal intensity before and after contrast enhancement. Eleven male volunteers (mean age 57.1 years; range 36-81 years) were examined with a fat-suppressed ultrashort TE (= 0.08 ms) pulse sequence. The studies were repeated after the administration of intravenous gadodiamide. The MR scans were examined for gland morphology and signal intensity before and after enhancement. Endocrinological evaluation included baseline pituitary function tests and a glucagon stimulatory test to assess pituitary cortisol and growth hormone reserve. High signal intensity was observed in the anterior pituitary relative to the brain in nine of the 11 subjects. These regions involved the whole of the anterior pituitary in three subjects, were localised to one side in two examples and were seen inferiorly in three subjects. Signal intensities relative to the brain increased with age, with a peak around the sixth or seventh decade and decreasing thereafter. Overall, the pituitary function tests were considered to be within normal limits and did not correlate with pituitary gland signal intensity. The anterior pituitary shows increased signal intensity in normal subjects when examined with T{sub 1}-weighted ultrashort TE pulse sequences. The cause of this increased intensity is unknown, but fibrosis and iron deposition are possible candidates. The variation in signal intensity with age followed the temporal pattern of iron content observed at post mortem. No relationship with endocrine status was observed. (orig.)

Measurement of x-ray emission and thermal transport in near-solid-density plasmas heated by 130 fs laser pulses

International Nuclear Information System (INIS)

Young, B.K.; Wilson, B.G.; Price, D.F.; Stewart, R.E.

1998-01-01

Near-solid-density plasmas with peak temperatures of 370±50 eV have been generated using a high-contrast (∼10 -7 ), 400 nm, 130 fs laser pulse of intensity 3x10 17 Wcm -2 at the Ultrashort Pulse Laser at Lawrence Livermore National Laboratory. The x-ray-emission spectra from thin tracer layers of germanium, tamped by layers of plastic, were measured as a function of target depth. The results qualitatively agree with calculations based on detailed local thermodynamic equilibrium (LTE) and modified non-LTE spectroscopic opacity models using plasma conditions determined using LASNEX hydrodynamic simulations. No evidence of thermal flux inhibition into the bulk target material was observed. The experiments and detailed simulations are presented. copyright 1998 The American Physical Society

Trichromatic π-Pulse for Ultrafast Total Inversion of a Four-Level Ladder System

Directory of Open Access Journals (Sweden)

Carles Serrat

2015-11-01

Full Text Available We present a numerical solution for complete population inversion in a four-level ladder system obtained by using a full π-pulse illumination scheme with resonant ultrashort phase-locked Gaussian laser pulses. We find that a set of pulse areas such as √3π , √2π , and √3π completely inverts the four-level system considering identical effective dipole coupling coefficients. The solution is consistent provided the involved electric fields are not too strong and it is amply accurate also in the case of diverse transition dipole moments. We study the effect of detuning and chirp of the laser pulses on the complete population inversion using the level structure of atomic sodium interacting with ps and fs pulses as an example. Our result opens the door for multiple applications such as efficient ultrashort pulse lasing in the UV or the engineering of quantum states for quantum computing.

Formation of a fine-dispersed liquid-metal target under the action of femto- and picosecond laser pulses for a laser-plasma radiation source in the extreme ultraviolet range

Energy Technology Data Exchange (ETDEWEB)

Vinokhodov, A Yu; Krivokorytov, M S [EUV Labs, Ltd., Troitsk, Moscow (Russian Federation); Koshelev, K N; Krivtsun, V M; Sidelnikov, Yu V; Medvedev, V V; Kompanets, V O; Melnikov, A A; Chekalin, S V [Institute of Spectroscopy, Russian Academy of Sciences, Troitsk, Moscow (Russian Federation)

2016-01-31

We report the results of studying the dynamics of deformation and fragmentation of liquid-metal droplets under the action of ultrashort laser pulses. The experiments have been performed to optimise the shape of the droplet target used in extreme ultraviolet (EUV) radiation sources based on the laser-produced plasma using the pre-pulse technology. The pre-pulse is generated by a system incorporating a master Ti : sapphire oscillator and a regenerative amplifier, allowing one to vary the pulse duration from 50 fs to 50 ps. The power density of laser radiation at the droplet target, averaged over the pulse duration and spatial coordinates, has reached 3 × 10{sup 15} W cm{sup -2}. The production of liquid-metal droplets has been implemented by means of a droplet generator based on a nozzle with a ring piezoceramic actuator. The droplet material is the eutectic indium – tin alloy. The droplet generator could operate in the droplet and jet regime with a maximal rate of stable operation 5 and 150 kHz, respectively. The spatial stability of droplet position σ = 1% – 2% of its diameter is achieved. The size of the droplets varied within 30 – 70 μm, their velocity was 2 – 8 m s{sup -1} depending on the operation regime. (interaction of laser radiation with matter. laser plasma)

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.

Role of thermal stresses on pulsed laser irradiation of thin films under conditions of microbump formation and nonvaporization forward transfer

Science.gov (United States)

Meshcheryakov, Yuri P.; Shugaev, Maxim V.; Mattle, Thomas; Lippert, Thomas; Bulgakova, Nadezhda M.

2013-11-01

This paper presents a theoretical analysis of the processes in thin solid films irradiated by short and ultrashort laser pulses in the regimes of film structuring and laser-induced forward transfer. The regimes are considered at which vaporization of the film materials is insignificant and film dynamics is governed mainly by mechanical processes. Thermoelastoplastic modeling has been performed for a model film in one- and two-dimensional geometries. A method has been proposed to estimate the height of microbumps produced by nanosecond laser irradiation of solid films. Contrary to femtosecond laser pulses, in nanosecond pulse regimes, stress waves across the film are weak and cannot induce film damage. The main role in laser-induced dynamics of irradiated films is played by radial thermal stresses which lead to the formation of a bending wave propagating along the film and drawing the film matter to the center of the irradiation spot. The bending wave dynamics depends on the hardness of the substrate underlying the film. The causes of the receiver substrate damage sometimes observed upon laser-induced forward transfer in the scheme of the direct contact between the film and the receiver are discussed.

Theoretical study of relativistic corrections induced by an ultra-short and intense light pulse in matter

International Nuclear Information System (INIS)

Hinschberger Schreiber, Yannick

2012-01-01

This thesis focuses on the relativistic corrections induced by an ultra-short and intense light pulse in condensed matter. It is part of the new theme of the coherent ultra-fast demagnetization of ferromagnetic systems induced by a femtosecond laser pulse [Nature, 5, 515 (2009)] [1]. A relativistic coupling between spins and photons has been proposed to explain the experimental results obtained in [1]. The first part of this work focuses on the nonrelativistic limit of the Dirac's formalism. By means of the Foldy-Wouthuysen transformation the nonrelativistic approximation of the external-electromagnetic-field Dirac equation to fifth order in powers of 1/m is obtained. Generalizing this result we postulate a general expression of the direct spin-field electronic Hamiltonian valid at any order in 1/m. A similar work is performed on a two-interacting electrons system described with the Breit Hamiltonian, whose the diagonalization at third order in 1/m illustrates an original coupling between the spin, the coulomb interaction and the time-dependent external electromagnetic field. In a second part, a classical model is developed for modeling ultrafast nonlinear coherent magneto-optical experiments performed on ferromagnetic thin films. Theoretical predictions of the Faraday rotation angles are compared to available experimental values and give meaningful insights about the physical mechanisms underlying the observed coherent magneto-optical phenomena. The crucial role played by the spin-orbit mechanism resulting from the direct interaction between the external electric field of the laser and the electron spins of the sample is underlined. (author) [fr

Two-temperature hydrodynamics of laser-generated ultrashort shock waves in elasto-plastic solids

International Nuclear Information System (INIS)

Ilnitsky, Denis K; Migdal, Kirill P; Khokhlov, Viktor A; Inogamov, Nail A; Petrov, Yurii V; Anisimov, Sergey I; Zhakhovsky, Vasily V; Khishchenko, Konstantin V

2014-01-01

Shock-wave generation by ultrashort laser pulses opens new doors for study of hidden processes in materials happened at an atomic-scale spatiotemporal scales. The poorly explored mechanism of shock generation is started from a short-living two-temperature (2T) state of solid in a thin surface layer where laser energy is deposited. Such 2T state represents a highly non-equilibrium warm dense matter having cold ions and hot electrons with temperatures of 1-2 orders of magnitude higher than the melting point. Here for the first time we present results obtained by our new hybrid hydrodynamics code combining detailed description of 2T states with a model of elasticity together with a wide-range equation of state of solid. New hydro-code has higher accuracy in the 2T stage than molecular dynamics method, because it includes electron related phenomena including thermal conduction, electron-ion collisions and energy transfer, and electron pressure. From the other hand the new code significantly improves our previous version of 2T hydrodynamics model, because now it is capable of reproducing the elastic compression waves, which may have an imprint of supersonic melting like as in MD simulations. With help of the new code we have solved a difficult problem of thermal and dynamic coupling of a molten layer with an uniaxially compressed elastic solid. This approach allows us to describe the recent femtosecond laser experiments.

Interaction of ultra-high intensity laser pulse with a mass limited targets

International Nuclear Information System (INIS)

Andreev, A.A.; Platonov, K.Yu.; Limpouch, J.; Psikal, J.; Kawata, S.

2006-01-01

Complete test of publication follows. Ultra-high intensity laser pulses may be produced now via CPA scheme by using very short laser pulses of a relatively low energy. Interaction of such pulses with massive target is not very efficient as the energy delivered to charged particles spreads out quickly over large distances and it is redistributed between many secondary particles. One possibility to limit this undesirable energy spread is to use mass limited targets (MLT), for example droplets, big clusters or small foil sections. This is an intermediate regime in target dimensions between bulk solid and nanometer-size atomic cluster targets. A few experimental and theoretical studies have been carried out on laser absorption, fast particle generation and induced nuclear fusion reactions in the interaction of ultrashort laser pulses with MLT plasma. We investigate here laser interactions with MLT via 2D3V relativistic electromagnetic PIC simulations. We assume spherical droplet as a typical MLT. However, the sphere is represented in 2D simulations by an infinite cylinder irradiated uniformly along its length. We assume that MLT is fully ionized before main pulse interaction either due to insufficient laser contrast or due to a prepulse. For simplicity, we assume homogeneous plasma of high initial temperature. We analyze the interaction of relativistic laser pulses of various polarizations with targets of different shapes, such as a foil, quadrant and sphere. The mechanisms of laser absorption, electron and ion acceleration are clarified for different laser and target parameters. When laser interacts with the target front side, kinetic energy of electrons rises rapidly with fast oscillations in the kinetic and field energy, caused by electron oscillations in the laser field. Small energy oscillations, observed later, are caused by the electron motion back and forth through the droplet. Approximately 40% of laser energy is transferred to the kinetic energy of electrons

Effect of laser pulse energies in laser induced breakdown spectroscopy in double-pulse configuration

International Nuclear Information System (INIS)

Benedetti, P.A.; Cristoforetti, G.; Legnaioli, S.; Palleschi, V.; Pardini, L.; Salvetti, A.; Tognoni, E.

2005-01-01

In this paper, the effect of laser pulse energy on double-pulse laser induced breakdown spectroscopy signal is studied. In particular, the energy of the first pulse has been changed, while the second pulse energy is held fixed. A systematic study of the laser induced breakdown spectroscopy signal dependence on the interpulse delay is performed, and the results are compared with the ones obtained with a single laser pulse of energy corresponding to the sum of the two pulses. At the same time, the crater formed at the target surface is studied by video-confocal microscopy, and the variation in crater dimensions is correlated to the enhancement of the laser induced breakdown spectroscopy signal. The results obtained are consistent with the interpretation of the double-pulse laser induced breakdown spectroscopy signal enhancement in terms of the changes in ambient gas pressure produced by the shock wave induced by the first laser pulse

Mode-locking of a terahertz laser by direct phase synchronization.

Science.gov (United States)

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

2012-09-10

A novel scheme to achieve mode-locking of a multimode laser is demonstrated. Traditional methods to produce ultrashort laser pulses are based on modulating the cavity gain or losses at the cavity roundtrip frequency, favoring the pulsed emission. Here, we rather directly act on the phases of the modes, resulting in constructive interference for the appropriated phase relationship. This was performed on a terahertz quantum cascade laser by multimode injection seeding with an external terahertz pulse, resulting in phase mode-locked terahertz laser pulses of 9 ps duration, characterized unambiguously in the time domain.

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.

Optimal initiation of electronic excited state mediated intramolecular H-transfer in malonaldehyde by UV-laser pulses

Science.gov (United States)

Nandipati, K. R.; Singh, H.; Nagaprasad Reddy, S.; Kumar, K. A.; Mahapatra, S.

2014-12-01

Optimally controlled initiation of intramolecular H-transfer in malonaldehyde is accomplished by designing a sequence of ultrashort (~80 fs) down-chirped pump-dump ultra violet (UV)-laser pulses through an optically bright electronic excited [ S 2 ( π π ∗)] state as a mediator. The sequence of such laser pulses is theoretically synthesized within the framework of optimal control theory (OCT) and employing the well-known pump-dump scheme of Tannor and Rice [D.J. Tannor, S.A. Rice, J. Chem. Phys. 83, 5013 (1985)]. In the OCT, the control task is framed as the maximization of cost functional defined in terms of an objective function along with the constraints on the field intensity and system dynamics. The latter is monitored by solving the time-dependent Schrödinger equation. The initial guess, laser driven dynamics and the optimized pulse structure (i.e., the spectral content and temporal profile) followed by associated mechanism involved in fulfilling the control task are examined in detail and discussed. A comparative account of the dynamical outcomes within the Condon approximation for the transition dipole moment versus its more realistic value calculated ab initio is also presented.

Photoelectron emission from LiF surfaces by ultrashort electromagnetic pulses

International Nuclear Information System (INIS)

Acuna, M. A.; Gravielle, M. S.

2011-01-01

Energy- and angle-resolved electron emission spectra produced by incidence of ultrashort electromagnetic pulses on a LiF(001) surface are studied by employing a distorted-wave method named the crystal surface-Volkov (CSV) approximation. The theory makes use of the Volkov phase to describe the action of the external electric field on the emitted electron, while the electron-surface interaction is represented within the tight-binding model. The CSV approach is applied to investigate the effects introduced by the crystal lattice when the electric field is oriented parallel to the surface plane. These effects are essentially governed by the vector potential of the external field, while the influence of the crystal orientation was found to be negligible.

Laser microprocessing of steel with radially and azimuthally polarized femtosecond vortex pulses

International Nuclear Information System (INIS)

Allegre, O J; Perrie, W; Edwardson, S P; Dearden, G; Watkins, K G

2012-01-01

The use of a liquid-crystal spatial light modulator (SLM) device to convert a linearly polarized femtosecond laser beam into a radially or azimuthally polarized vortex beam is demonstrated. In order to verify the state of polarization at the focal plane, laser induced periodic surface structures (LIPSS) are produced on stainless steel, imprinting the complex vectorial polarization structures and confirming the efficacy of the SLM in producing the desired polarization modes. Stainless steel plates of various thicknesses are micromachined with the radially and azimuthally polarized vortex beams and the resulting cut-outs are analysed. The process efficiency and quality of each mode are compared with those of circular polarization. Radial polarization is confirmed to be the most efficient mode for machining high-aspect-ratio (depth/width > 3) channels thanks to its relatively higher absorptivity. Following our microprocessing tests, liquid-crystal SLMs emerged as a flexible off-the-shelf tool for producing radially and azimuthally polarized beams in existing ultrashort-pulse laser microprocessing systems. (paper)

High-resolution X-ray spectroscopy of hollow atoms created in plasma heated by subpicosecond laser radiation

International Nuclear Information System (INIS)

Faenov, A.Ya.; Magunov, A.I.; Pikuz, T.A.

1997-01-01

The investigations of ultrashort (0.4-0.6 ps) laser pulse radiation interaction with solid targets have been carried out. The Trident subpicosecond laser system was used for plasma creation. The X-ray plasma emission was investigated with the help of high-resolution spectrographs with spherically bent mica crystals. It is shown that when high contrast ultrashort laser pulses were used for plasma heating its emission spectra could not be explained in terms of commonly used theoretical models, and transitions in so called hollow atoms must be taken into account for adequate description of plasma radiation

Nonlinear dynamics in integrated coupled DFB lasers with ultra-short delay.

Science.gov (United States)

Liu, Dong; Sun, Changzheng; Xiong, Bing; Luo, Yi

2014-03-10

We report rich nonlinear dynamics in integrated coupled lasers with ultra-short coupling delay. Mutually stable locking, period-1 oscillation, frequency locking, quasi-periodicity and chaos are observed experimentally. The dynamic behaviors are reproduced numerically by solving coupled delay differential equations that take the variation of both frequency detuning and coupling phase into account. Moreover, it is pointed out that the round-trip frequency is not involved in the above nonlinear dynamical behaviors. Instead, the relationship between the frequency detuning Δν and the relaxation oscillation frequency νr under mutual injection are found to be critical for the various observed dynamics in mutually coupled lasers with very short delay.

Study of ablation on surfaces of nuclear-use metals irradiated with Femtosecond laser

International Nuclear Information System (INIS)

Nogueira, Alessandro F.; Samad, Ricardo E.; Vieira Junior, Nilson D.; Rossi, Wagner de

2017-01-01

The use of ultrashort pulsed lasers is an alternative for micro-machining in metal surfaces, with diverse applications in several industrial areas, such as aeronautics, aerospace, naval, nuclear, among others, where there is a growing concern with reliability in service. In this work, micro-machining were performed on titanium surfaces using femtosecond ultrashort pulses. Such a process resulted in minimal heat transfer to the material, thus avoiding and surface deformation of the titanium plate and the formation of resolidified material in the ablated region, which are drawbacks present in the use of the long pulsed keyed laser of the order of nanoseconds. Three types of micro-machining were performed, with variations in the distances between the machined lines. It was also verified that the wettability increases when there is an increase in the distance between machined lines. Finally, in order to change the surface with minimal removal of material, it has been found that the use of ultra-short pulse lasers provide great benefits for the integrity of the ablated material. This initial study is the starting point for the study of other metals, such as Maraging Steels and Zircaloy that will be the target of future work. (author)

Study of ablation on surfaces of nuclear-use metals irradiated with Femtosecond laser

Energy Technology Data Exchange (ETDEWEB)

Nogueira, Alessandro F.; Samad, Ricardo E.; Vieira Junior, Nilson D.; Rossi, Wagner de, E-mail: alessandro.nogueira@usp.br, E-mail: resamad@ipen.br [Centro Tecnologico da Marinha em Sao Paulo (CTMSP), Sorocaba, SP (Brazil); Faculdade de Engenharia de Sorocaba (FACENS), Ipero, SP (Brazil); Instituto de Pesquisas Energeticas e Nucleares (IPEN/CNEN-SP), Sao Paulo, SP (Brazil)

2017-11-01

The use of ultrashort pulsed lasers is an alternative for micro-machining in metal surfaces, with diverse applications in several industrial areas, such as aeronautics, aerospace, naval, nuclear, among others, where there is a growing concern with reliability in service. In this work, micro-machining were performed on titanium surfaces using femtosecond ultrashort pulses. Such a process resulted in minimal heat transfer to the material, thus avoiding and surface deformation of the titanium plate and the formation of resolidified material in the ablated region, which are drawbacks present in the use of the long pulsed keyed laser of the order of nanoseconds. Three types of micro-machining were performed, with variations in the distances between the machined lines. It was also verified that the wettability increases when there is an increase in the distance between machined lines. Finally, in order to change the surface with minimal removal of material, it has been found that the use of ultra-short pulse lasers provide great benefits for the integrity of the ablated material. This initial study is the starting point for the study of other metals, such as Maraging Steels and Zircaloy that will be the target of future work. (author)

Nonlinear Dynamics of Ultrashort Long-Range Surface Plasmon Polariton Pulses in Gold Strip Waveguides

DEFF Research Database (Denmark)

Lysenko, Oleg; Bache, Morten; Olivier, Nicolas

2016-01-01

We study experimentally and theoretically nonlinear propagation of ultrashort long-range surface plasmon polaritons in gold strip waveguides. The nonlinear absorption of the plasmonic modes in the waveguides is measured with femtosecond pulses revealing a strong dependence of the third......-order nonlinear susceptibility of the gold core on the pulse duration and layer thickness. A comprehensive model for the pulse duration dependence of the third-order nonlinear susceptibility is developed on the basis of the nonlinear Schrödinger equation for plasmonic mode propagation in the waveguides....... The model accounts for the intrinsic delayed (noninstantaneous) nonlinearity of free electrons of gold as well as the thickness of the gold film and is experimentally verified. The obtained results are important for the development of active plasmonic and nanophotonic components....

Strong field laser physics

CERN Document Server

2008-01-01

Since the invention of the laser in the 1960s, people have strived to reach higher intensities and shorter pulse durations. High intensities and ultrashort pulse durations are intimately related. Recent developments have shown that high intensity lasers also open the way to realize pulses with the shortest durations to date, giving birth to the field of attosecond science (1 asec = 10-18s). This book is about high-intensity lasers and their applications. The goal is to give an up to date introduction to the technology behind these laser systems and to the broad range of intense laser applications. These applications include AMO (atomic molecular and optical) physics, x-ray science, attosecond science, plasma physics and particle acceleration, condensed matter science and laser micromachining, and finally even high-energy physics.

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...

Intense isolated attosecond pulse generation from relativistic laser plasmas using few-cycle laser pulses

International Nuclear Information System (INIS)

Ma, Guangjin; Dallari, William; Borot, Antonin; Tsakiris, George D.; Veisz, Laszlo; Krausz, Ferenc; Yu, Wei

2015-01-01

We have performed a systematic study through particle-in-cell simulations to investigate the generation of attosecond pulse from relativistic laser plasmas when laser pulse duration approaches the few-cycle regime. A significant enhancement of attosecond pulse energy has been found to depend on laser pulse duration, carrier envelope phase, and plasma scale length. Based on the results obtained in this work, the potential of attaining isolated attosecond pulses with ∼100 μJ energy for photons >16 eV using state-of-the-art laser technology appears to be within reach

Low-level ultrahigh-frequency and ultrashort-pulse blue laser irradiation enhances osteoblast extracellular calcification by upregulating proliferation and differentiation via transient receptor potential vanilloid 1.

Science.gov (United States)

Mikami, Risako; Mizutani, Koji; Aoki, Akira; Tamura, Yukihiko; Aoki, Kazuhiro; Izumi, Yuichi

2018-04-01

Low-level laser irradiation (LLLI) exerts various biostimulative effects, including promotion of wound healing and bone formation; however, few studies have examined biostimulation using blue lasers. The purpose of this study was to investigate the effects of low-level ultrahigh-frequency (UHF) and ultrashort-pulse (USP) blue laser irradiation on osteoblasts. The MC3T3-E1 osteoblast cell line was used in this study. Following LLLI with a 405 nm newly developed UHF-USP blue laser (80 MHz, 100 fs), osteoblast proliferation, and alkaline phosphatase (ALP) activity were assessed. In addition, mRNA levels of the osteoblast differentiation markers, runt-related transcription factor 2 (Runx2), osterix (Osx), alkaline phosphatase (Alp), and osteopontin (Opn) was evaluated, and extracellular calcification was quantified. To clarify the involvement of transient receptor potential (TRP) channels in LLLI-induced biostimulation, cells were treated prior to LLLI with capsazepine (CPZ), a selective inhibitor of TRP vanilloid 1 (TRPV1), and subsequent proliferation and ALP activity were measured. LLLI with the 405 nm UHF-USP blue laser significantly enhanced cell proliferation and ALP activity, compared with the non-irradiated control and LLLI using continuous-wave mode, without significant temperature elevation. LLLI promoted osteoblast proliferation in a dose-dependent manner up to 9.4 J/cm 2 and significantly accelerated cell proliferation in in vitro wound healing assay. ALP activity was significantly enhanced at doses up to 5.6 J/cm 2 , and expression of Osx and Alp mRNAs was significantly increased compared to that of the control on days 3 and 7 following LLLI at 5.6 J/cm 2 . The extent of extracellular calcification was also significantly higher as a result of LLLI 3 weeks after the treatment. Measurement of TRPV1 protein expression on 0, 3, and 7 days post-irradiation revealed no differences between the LLLI and control groups; however, promotion of cell

Preformed transient gas channels for laser wakefield particle acceleration

International Nuclear Information System (INIS)

Wood, W.M.

1994-01-01

Acceleration of electrons by laser-driven plasma wake fields is limited by the range over which a laser pulse can maintain its intensity. This distance is typically given by the Rayleigh range for the focused laser beam, usually on the order of 0.1 mm to 1 mm. For practical particle acceleration, interaction distances on the order of centimeters are required. Therefore, some means of guiding high intensity laser pulses is necessary. Light intensities on the order of a few times 10 17 W/cm 2 are required for laser wakefield acceleration schemes using near IR radiation. Gas densities on the order of or greater than 10 17 cm -3 are also needed. Laser-atom interaction studies in this density and intensity regime are generally limited by the concomitant problems in beam propagation introduced by the creation of a plasma. In addition to the interaction distance limit imposed by the Rayleigh range, defocusing of the high intensity laser pulse further limits the peak intensity which can be achieved. To solve the problem of beam propagation limitations in laser-plasma wakefield experiments, two potential methods for creating transient propagation channels in gaseous targets are investigated. The first involves creation of a charge-neutral channel in a gas by an initial laser pulse, which then is ionized by a second, ultrashort, high-intensity pulse to create a waveguide. The second method involves the ionization of a gas column by an ultrashort pulse; a transient waveguide is formed by the subsequent expansion of the heated plasma into the neutral gas