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Electron-photon drag effect in a semiconductor superlattice subjected to a high electric field
2007-01-01
Drag of charge carriers in a superlattice subjected to a constant axially oriented electric field by an electromagnetic wave also propagating along the axis is considered. The drag-current density is calculated and its dependence on the constant-field strength E1 and the electromagnetic-wave intensity I is analyzed. Reversals of the current direction are found to occur for certain values of E1 and I
Negatively charged polaritons in a semiconductor microcavity
We study by reflection spectroscopy the cavity polaritons in a structure consisting of a single GaAs/AlAs quantum well that contains a low density (n{sub e}) two dimensional electron gas, and is embedded in a {lambda}-wide GaAs/Ga{sub 1{minus}x}Al{sub x}As microcavity (MC). For n{sub e}{lt}5{times}10{sup 10} cm{sup {minus}2}, negatively charged MC polaritons are photoexcited, as a result of the strong coupling of the MC photon and the negatively charged [(e1:hh1)1S+e] exciton (X{sup {minus}}). The charged polaritons have several properties that are distinct from those of neutral polaritons [which are formed from the neutral (e1:hh1)1S (X) and (e1:lh1)1S excitons] (a) The MC-photon{endash}X{sup {minus}} coupling strength increases as {radical}n{sub e}. This is analogous to the dependence of the confined-photon{endash}atom coupling on the density of free atoms in a metallic cavity. (b) The charged polaritons have a nonvanishing electric charge that is due to the bare X{sup {minus}} charge. (c) Since the energy difference between the bare X and X{sup {minus}} excitons is smaller than the coupling strength of each one with the MC photon, these two bare exciton states are admixed in the charged polariton states. The experimental reflection spectra were analyzed using a model of coupled quantum oscillators representing the excitons and the confined photon mode. From the fitted spectra it is deduced that the X{sup {minus}} coupling strength increases with increasing n{sub e}, and there is an oscillator strength transfer from X to X{sup {minus}}. Using the cavity polariton wave functions (which are obtained from the model fitting) we calculate the effective charge and mass of all the cavity polaritons as a function of the MC-photon energy. The calculated (e/m){sub eff} ratio reaches a value {similar_to}200 times larger than that of the free electron in a bare GaAs quantum well. Using the calculated dependence of the effective polariton charge and mass on the in-plane wave vector and the detuning energy, the maximum distance that the charged polariton can drift under an applied electric field is calculated. The charged polariton is expected to drift a distance at least 10 times larger than the bare X{sup {minus}}.
Negatively charged polaritons in a semiconductor microcavity
2001-06-15
We study by reflection spectroscopy the cavity polaritons in a structure consisting of a single GaAs/AlAs quantum well that contains a low density (n{sub e}) two dimensional electron gas, and is embedded in a {lambda}-wide GaAs/Ga{sub 1{minus}x}Al{sub x}As microcavity (MC). For n{sub e}{lt}5{times}10{sup 10} cm{sup {minus}2}, negatively charged MC polaritons are photoexcited, as a result of the strong coupling of the MC photon and the negatively charged [(e1:hh1)1S+e] exciton (X{sup {minus}}). The charged polaritons have several properties that are distinct from those of neutral polaritons [which are formed from the neutral (e1:hh1)1S (X) and (e1:lh1)1S excitons] (a) The MC-photon{endash}X{sup {minus}} coupling strength increases as {radical}n{sub e}. This is analogous to the dependence of the confined-photon{endash}atom coupling on the density of free atoms in a metallic cavity. (b) The charged polaritons have a nonvanishing electric charge that is due to the bare X{sup {minus}} charge. (c) Since the energy difference between the bare X and X{sup {minus}} excitons is smaller than the coupling strength of each one with the MC photon, these two bare exciton states are admixed in the charged polariton states. The experimental reflection spectra were analyzed using a model of coupled quantum oscillators representing the excitons and the confined photon mode. From the fitted spectra it is deduced that the X{sup {minus}} coupling strength increases with increasing n{sub e}, and there is an oscillator strength transfer from X to X{sup {minus}}. Using the cavity polariton wave functions (which are obtained from the model fitting) we calculate the effective charge and mass of all the cavity polaritons as a function of the MC-photon energy. The calculated (e/m){sub eff} ratio reaches a value {similar_to}200 times larger than that of the free electron in a bare GaAs quantum well. Using the calculated dependence of the effective polariton charge and mass on the in-plane wave vector and the detuning energy, the maximum distance that the charged polariton can drift under an applied electric field is calculated. The charged polariton is expected to drift a distance at least 10 times larger than the bare X{sup {minus}}.
Is there a low energy enhancement in the photon strength function in molybdenum?
2008-01-30
Recent claims of a low energy enhancement in the photon strength function of {sup 96}Mo are investigated. Using the DANCE detector the gamma-ray spectra following resonance neutron capture was measured. The spectrum fitting method was used to indirectly extract a photon strength function from the gamma-ray spectra. No strong low energy enhancement in the photon strength function was found.
The photoresponse of stable N=82 nuclei below 10 MeV
2006-11-27
High resolution photon scattering experiments were performed at the 10 MeV bremsstrahlung facility of the electron accelerator S-DALINAC at TU Darmstadt to investigate the semi-magic N=82 nuclei {sup 138}Ba, {sup 140}Ce, {sup 142}Nd and {sup 144}Sm. Energies and absolute strengths of dipole transitions below 10 MeV were determined in a model independent way. A concentration of electric dipole excitations exhausting up to 1% of the isovector E1 energy weighted sum rule is observed in all four nuclei around 6.5 MeV. Calculations in the framework of the Quasiparticle-Phonon Model (QPM) reproduce the gross experimental features.
The photoresponse of stable N=82 nuclei below 10 MeV
2006-01-01
High resolution photon scattering experiments were performed at the 10 MeV bremsstrahlung facility of the electron accelerator S-DALINAC at TU Darmstadt to investigate the semi-magic N=82 nuclei 138Ba, 140Ce, 142Nd and 144Sm. Energies and absolute strengths of dipole transitions below 10 MeV were determined in a model independent way. A concentration of electric dipole excitations exhausting up to 1% of the isovector E1 energy weighted sum rule is observed in all four nuclei around 6.5 MeV. Calculations in the framework of the Quasiparticle-Phonon Model (QPM) reproduce the gross experimental features
Corrugated fiberboard as a positioning insert for patients undergoing radiotherapy
2010-01-01
We have developed a new body fixation system for single patient use, which consists of a vacuum cushion, a thermoplastic fixation sheet which is used to suppress involuntary and voluntary patient movement, and a triple-wall corrugated fiberboard base plate to which both the vacuum cushion and the thermoplastic sheet are affixed. To evaluate the characteristics of the fiberboard as a patient-positioning insert, the photon beam attenuation of a fiberboard base plate, a carbon-fiber base plate, and a vacuum-formed cushion were compared. The strength of the fiberboard was also evaluated. The attenuation for the carbon-fiber base plate was 3.7% and 2.6% in 4 MV and 10 MV photon beams, respectively, while the results were less for the fiberboard base plate, id est (i.e.) 1.9% and 1.6%. The vacuum-formed cushion had a minimal effect on transmission. None of the materials subsided ...
Photon Spectroscopy Of Heavy Quarkonia
We have studied the inclusive photon spectrum in y (2S), ϒ(2S), and ϒ(3 S) decays using the CLEO III detector. We present the most precise measurements of electric dipole (E1) photon transition rates and photon energies for y (2S) → γχ
Dissipation induced Tonks-Girardeau gas of photons
2009-08-17
A scheme for the generation of a Tonks-Girardeau gas of photons with purely dissipative interaction is described. We put forward a master equation approach for the description of stationary light in atomic four-level media and show that, under suitable conditions, two particle decays are the dominant photon loss mechanism. These dissipative two-photon losses increase the interaction strength by at least one order of magnitude as compared to dispersive two-photon processes and can drive the photons into the Tonks-Girardeau regime. Different scenarios for the observation of fermionic correlations between photons in the Tonks-Girardeau gas regime are discussed.
Quantum limit of photon-photon interactions using electromagnetically induced transparency
1999-02-02
Quantum limit of dissipation-free photon-photon interactions at the few photon level is studied in the context of giant Kerr nonlinearities in cavity electromagneti cally induced transparency (EIT). It is shown that photon-photon interaction is largest when the cavity contains a sing le atom. In contrast to conventional nonlinearities, increasing the number of atoms cannot in crease the interaction strength but will in general degrade the performance by enhancing di spersion. In the non-perturbative regime, the single-atom photon-photon interaction can be limited by lossy states excited from long-lived EIT states. Asymptotically, in the strong coupling limit, photon-photon interaction is determined by the single photon-atom coupling strength. Photon blockade occurs for single atoms but only partial blockade can occur for low dispersion and not at all in the high-dispersion limit of the multi-atom case.
Light-shift-induced photonic nonlinearities
2008-01-01
We propose a new method to produce self- and cross-Kerr photonic nonlinearities, using light-induced Stark shifts due to the interaction of a cavity mode with atoms. The proposed experimental set-up is simpler than in previous approaches, while the strength of the nonlinearity obtained with a single atom is the same as in the setting based on electromagnetically induced transparency. Furthermore our scheme can be applied to engineer effective photonic nonlinear interactions whose strength increases with the number of atoms coupled to the cavity mode, leading to photon-photon interactions several orders of magnitude larger than previously considered possible
Resonance parameters of the first 1/2+ state in 9Be and astrophysical implications
2010-06-14
Spectra of the 9Be(e,e') reaction have been measured at the S-DALINAC at an electron energy E_0 = 73 MeV and scattering angles of 93{\\deg} and 141{\\deg} with high energy resolution up to excitation energies E_x = 8 MeV. The astrophysically relevant resonance parameters of the first excited 1/2+ state of 9Be have been extracted in a one-level approximation of R-matrix theory resulting in a resonance energy E_R = 1.748(6) MeV and width Gamma_R = 274(8) keV in good agreement with the latest 9Be(gamma,n) experiment but with considerably improved uncertainties. However, the reduced B(E1) transition strength deduced from an extrapolation of the (e,e') data to the photon point is a factor of two smaller. Implications of the new results for a possible production of 12C in neutron-rich astrophysical scenarios are discussed.
Optical constants of Cu(In0.7Ga0.3)5Se8 and Cu(In0.4Ga0.6)5Se8 crystals
2010-01-01
Variable angle spectroscopic ellipsometry has been applied to characterize the optical constants of bulk Cu(In0.7Ga0.3)5Se8 and Cu(In0.4Ga0.6)5Se8 crystals grown by the Bridgman method. The spectra were measured at room temperature over the energy range 0.8–4.4eV. Adachi’s model was used to calculate the dielectric functions as well as the spectral dependence of complex refractive index, absorption coefficient, and normal-incidence reflectivity. The calculated data are in good agreement with the experimental ones over the entire range of photon energies. The parameters such as strength, threshold energy, and broadening, corresponding to the E0, E1A, and E1B interband transitions, have been determined using the simulated annealing algorithm.
2009-01-01
The valence shell electronic structure of hexafluorobenzene (C6F6) has been studied both experimentally and theoretically. The absolute photoabsorption cross section has been measured between 6 and 42 eV, using synchrotron radiation, and is dominated by prominent broad bands associated with intravalence transitions. In contrast, the structure due to Rydberg excitations is weak, but series have been observed converging onto the X-tilde 2E1g, A-tile 2A2u, B-tilde 2B2u or C-tilde 2E2g limits. At photon energies above 13.7 eV the absorption bands become strongly perturbed, possibly as a result of Rydberg/valence state mixing, and Rydberg series can no longer be identified. The TDDFT approach has been used to calculate oscillator strengths and ...
Comparison of photon-photon and photon-magnetic field pair production rates
1983-01-01
Neutron stars have been proposed as the site of ..gamma..-ray burst activity and the copious supply of MeV photons admits the possibility of electron-positron pair production. If the neutron star magnetic field is sufficiently intense (> 10/sup 12/ G), both photon-photon (2..gamma..) and photon-magnetic field (1..gamma..) pair production should be important mechanisms. Rates for the two processes have been calculated using a Maxwellian distribution for the photons. The ratio of 1..gamma.. to 2..gamma.. pair production rates has been obtained as a function of photon temperature and magnetic field strength.
Comparison of photon-photon and photon-magnetic field pair production rates
1983-03-01
Neutron stars were proposed as the site of gamma-ray burst activity and the copious supply of MeV photons admits the possibility of electron-positron pair production. If the neutron star magnetic field is sufficiently intense ( 10 to the 12th power G), both photon-photon (2 gamma) and photon-magnetic field ( gamma) pair production should be important mechanisms. Rates for the two processes were calculated using a Maxwellian distribution for the photons. The ratio of 1 gamma to 2 gamma pair production rates was obtained as a function of photon temperature and magnetic field strength.
A multiexcitonic quantum dot in an optical microcavity
2006-04-19
We theoretically study the coupled modes of a medium-size quantum dot, which may confine a maximum of ten electron-hole pairs, and a single photonic mode of an optical microcavity. Ground-state and excitation energies, exciton-photon mixing in the wave functions and the emission of light from the microcavity are computed as functions of the pair-photon coupling strength, photon detuning, and polariton number.
Spectral distribution of the two-photon decay of He-like krypton
1995-08-01
The 2 {sup 1}S{sub 0} state in helium-like ions is forbidden to decay to the ground state by the emission of a single photon so the dominant decay mode is emission of two E1 photons. The energies of the individual photons have a continuous distribution with a broad peak at half the transition energy and the sum of the energies of the two photons is equal to the transition energy. The shape of the continuum single-photon spectrum provides a sensitive probe of the calculation of the transition probability for this decay and we have started a program to make a precision measurement of the spectral shape of the decay of the 2 {sup 1}S{sub 0} level in He-like krypton in order to test the calculations.
Lower bounds of altitudes for pulsar $\\gamma$-ray radiation
2009-12-03
Determining radiation location observationally plays a very important role in testing the pulsar radiation models. One-photon pair production in the strong magnetic field, $\\gamma-e^{+}e^{1}$, is one of the important physical processes in pulsar radiation mechanisms. Photons near pulsar surface with sufficient energy will be absorbed in the magnetosphere and the absorption optical depth for these GeV $\\gamma$-ray photons is usually large. In this paper, we include the aberrational, rotational and general relativistic effects and calculate the $\\gamma$-B optical depth for $\\gamma$-ray photons. Then we use the derived optical depth to determine the radiation altitude lower bounds for photons with given energies. As a case study, we calculate the lower bounds of radiation altitudes of Crab pulsar for photons with energy from 5 GeV to 1 TeV.
Measurement of Quantum Weak Values of Photon Polarization
2005-01-01
We experimentally determine weak values for a single photon's polarization, obtained via a weak measurement that employs a two-photon entangling operation, and postselection. The weak values cannot be explained by a semiclassical wave theory, due to the two-photon entanglement. We observe the variation in the size of the weak value with measurement strength, obtaining an average measurement of the S-1 Stokes parameter more than an order of magnitude outside of the operator's spectrum for the smallest measurement strengths. Publisher: American Physical Society Contributor: Blume, Martin Coverage: 2005-01-01T00:00:00Z
On search for hidden sector photons in Super-Kamiokande
2008-02-12
If hidden sector photons exist, they could be produced through oscillations of photons emitted by the Sun. We show that a search for these particles could be performed in Super-Kamiokande due to the presence in this detector of a large number of photomultiplier's (PMTs) with a relatively low noise and big size. These particles would penetrate the Earth shielding and would be detected by PMTs through their oscillations into real photons inside the PMTs vacuum volume. This would results in an increase of the PMT counting rate and it daily variations depending on the Earth position with respect to the Sun. The proposed search for this effect is sensitive to the photon-hidden photon mixing strength as small as ~10^{-6} for the hidden photon mass region ~10^{-3} - 10^{-1} eV and, in the case of nonobservation, could improve limits recently obtained from photon regeneration laser experiments for this mass region.
Spectroscopic features of low-energy excitations in skin nuclei
2010-04-27
Systematic studies of dipole and other multipole excitations in stable and exotic nuclei are discussed theoretically. Exploring the relation of the strengths of low-energy dipole and quadrupole pygmy resonances to the thickness of the neutron (proton) skin a close connection between static and dynamic properties of the nucleus is observed. The fine structure of low-energy dipole strength in 138Ba nucleus is revealed from E1 and spin-flip M1 strengths distributions.
Efficient Two-Photon Excited Amplified Spontaneous Emission from Organic Single Crystals
2010-01-01
E, E-1, 4-bis[4prime-(N,N-dibutylamino)styryl]-2,5-dimethoxy-benzene (DBASDMB) organic crystals with high crystalline quality, large size and excellent optical properties are prepared. The linear and nonlinear properties in the crystal are comparatively studied. The relaxation dynamics pumped by two-photon are very similar with that pumped by one-photon. The crystal exhibits very strong two-photon excited fluorescence and amplified spontaneous emission. Efficient two-photon absorption, reasonably high fluorescent quantum efficiency, and high crystal quality together with stimulated emission make organic crystals ideal for the application in frequency upconversion and other optoelectronic fields.
Effective photon-photon interaction in a two-dimensional 'photon fluid'
2004-01-01
We formulate an effective theory for the atom-mediated photon-photon interactions in a two-dimensional 'photon fluid' confined in a Fabry-Perot resonator. With the atoms modeled by a collection of anharmonic Lorentz oscillators, the effective interaction is evaluated to second order in the coupling constant (the anharmonicity parameter). The interaction has the form of a renormalized two-dimensional delta-function potential, with the renormalization scale determined by the physical parameters of the system, such as density of atoms and the detuning of the photons relative to the resonance frequency of the atoms. For realistic values of the parameters, the perturbation series has to be resummed, and the effective interaction becomes independent of the 'bare' strength of the anharmonic term. The resulting expression for the nonlinear Kerr susceptibility is ...
The gamma-ray Strength Function in Nuclear Astrophysics
2009-01-01
The gamma-ray strength function is a key statistical nuclear ingredient to the s-, r- and p-process nucleosynthesis of heavy elements. It has recently become apparent that extra gamma-ray strengths that appear near neutron threshold on top of the low-energy tail of GDR play an important role in neutron capture and photodisintegration. We discuss extra gamma-ray strengths of pigmy E1 and giant M1 nature based on the latest experimental photoneutron cross sections measured with laser Compton scattering gamma-rays
Radiative strength functions for E1 transitions in deformed even-even nuclei
1982-09-01
The radiative strength functions of reduced E1-transition probabilities for deformed nuclei are investigated in the region of the neutron binding energy. The average reduced radiative widths are computed. The results obtained are in agreement with the available experimental data. It is shown that allowance for the anharmonicity of the deformed nuclei leads to some slight changes in the strength functions in the region of the neutron binding energy. The effect of the ''tail'' of the giant dipole resonance on the strength function for an E1 transition in this energy is investigated.
Photon Pickup by Intense Poynting Flows
2003-11-18
It is suggested that a Poynting flux-dominated outflow with a sufficiently strong magnetic field can pick up hard X-ray photons when the magnetic field is of sufficient strength. The zeroth generation X-rays pair produce, and the pairs radiate extremely energetic first generation photons that could be detected by extensive air shower arrays and/or MILAGRO if they escape the production site intact. Giant flares from magnetars may thus yield bursts of UHE photons. GRB-associated Poynting flows may be unstable to pair production near their source, and their energy rapidly converted to pairs.
2009-01-01
Mirror dark matter provides a simple framework for which to explain the DAMA/LIBRA annual modulation signal consistently with the null results of the other direct detection experiments. The simplest possibility involves ordinary matter interacting with mirror dark matter via photon-mirror photon kinetic mixing of strength epsilonapprox10-9. We confirm that photon-mirror photon mixing of this magnitude is consistent with constraints from ordinary Big Bang nucleosynthesis as well as the more stringent constraints from cosmic microwave background measurements and large scale structure considerations
2009-01-01
Mirror dark matter provides a simple framework for which to explain the DAMA/LIBRA annual modulation signal consistently with the null results of the other direct detection experiments. The simplest possibility involves ordinary matter interacting with mirror dark matter via photon-mirror photon kinetic mixing of strength Formula Not Shown . We confirm that photon-mirror photon mixing of this magnitude is consistent with constraints from ordinary Big Bang nucleosynthesis as well as the more stringent constraints from cosmic microwave background measurements and large scale structure considerations.
Single photon nonlinearities using arrays of cold polar molecules
2009-02-24
We model single photon nonlinearities via the dipole-dipole interactions of cold polar molecules. We propose utilizing "dark state polaritons" to effectively couple photon and molecular states; through this framework, coherent control of the nonlinearity can be expressed and potentially used in an optical quantum computation architecture. Due to the dipole-dipole interaction the photons pick up a measurable nonlinear phase even in the single photon regime. A manifold of protected symmetric eigenstates is used as basis. Depending on the implementation, major sources of decoherence result from non-symmetric interactions and phonon dispersion. We discuss the strength of the nonlinearity per photon and the feasibility of this system.
Photon echo studies of photosynthetic light harvesting
2009-01-01
The broad linewidths in absorption spectra of photosynthetic complexes obscure information related to their structure and function. Photon echo techniques represent a powerful class of time-resolved electronic spectroscopy that allow researchers to probe the interactions normally hidden under broad linewidths with sufficient time resolution to follow the fastest energy transfer events in light harvesting. Here, we outline the technical approach and applications of two types of photon echo experiments: the photon echo peak shift and two-dimensional (2D) Fourier transform photon echo spectroscopy. We review several extensions of these techniques to photosynthetic complexes. Photon echo peak shift spectroscopy can be used to determine the strength of coupling between a pigment and its surroun...
Photon Splitting and Pair Conversion in Strong Magnetic Fields
2008-01-01
The magnetospheres of neutron stars provide a valuable testing ground for as-yet unverified theoretical predictions of quantum electrodynamics (QED) in strong electromagnetic fields. Exhibiting magnetic field strengths well in excess of a TeraGauss, such compact astrophysical environments permit the action of exotic mechanisms that are forbidden by symmetries in field-free regions. Foremost among these processes are single-photon pair creation, where a photon converts to an electron-positron pair, and magnetic photon splitting, where a single photon divides into two of lesser energy via the coupling to the external field. The pair conversion process is exponentially small in weak fields, and provides the leading order contribution to vacuum polarization. In contrast, photon splitting possesses no energy threshold and can operate in kinematic regimes where the ...
Analog E1 transitions and isospin mixing
2008-01-01
We investigate whether isospin mixing can be determined in a model-independent way from the relative strength of E1 transitions in mirror nuclei. The specific examples considered are the A=31 and A=35 mirror pairs, where a serious discrepancy between the strengths of 7/2--
2010-01-13
Because of the fundamental importance of Bell's theorem, a loophole-free demonstration of a violation of local realism (LR) is highly desirable. Here, we study violations of LR involving photon pairs. We quantify the experimental evidence against LR by using measures of statistical strength related to the Kullback-Leibler (KL) divergence, as suggested by W. van Dam, P. Grunwald and R. Gill [IEEE Trans. Inf. Theory. 51, 2812 (2005)]. Specifically, we analyze a test of LR with entangled states created from two independent polarized photons passing through a polarizing beam splitter. We numerically study the detection efficiency required to achieve a specified statistical strength for the rejection of LR depending on whether photon counters or detectors are used. Based on our results, we find that a test of LR free of the detection loophole requires photon counters with efficiency at least 89.71%, or photon detectors with efficiency at least 91.11%. For comparison, we also perform this analysis with ideal unbalanced Bell states, which are known to allow rejection of LR with detector efficiencies above 2/3.
On the isoscalar-isovector splitting of pygmy dipole structures
2009-06-01
The electric dipole response of $^{140}$Ce is investigated using the fully consistent relativistic quasiparticle random phase approximation. By analyzing the isospin structure of the E1 response, it is shown that the low-energy (pygmy) strength separates into two segments with different isospin character. The more pronounced pygmy structure at lower energy is composed of predominantly isoscalar states with surface-peaked transition densities. At somewhat higher energy the calculated E1 strength is primarily of isovector character, as expected for the low-energy tail of the giant dipole resonance. The results are in qualitative agreement with those obtained in recent $(\\gamma,\\gamma')$ and $(\\alpha,\\alpha'\\gamma)$ experiments, and provide a simple explanation for the splitting of low-energy E1 strength into two groups of states with different isospin structure and radial dependence of the corresponding transition densities.
Extra gamma-ray strength for 116,117Sn arising from pygmy dipole resonance
2010-01-01
Photoneutron cross sections were measured for 117Sn and 116Sn near neutron thresholds with quasi-monochromatic laser Compton scattering gamma-rays. The measured cross sections for 117Sn and 116Sn are strongly enhanced from the threshold behavior expected for L = 1 neutron emissions after E1 photoexcitation. This suggests the presence of extra gamma-ray strength in the low-energy tail of the giant dipole resonance. The present cross sections were analyzed together with radiative neutron capture cross sections for 116Sn within the framework of the statistical model calculation. It is shown that the extra gamma-ray strength can be interpreted as pygmy E1 resonance which was previously reported in the nuclear resonance fluorescence experiment for 116Sn ...
Electric dipole strength distribution below the E1 giant resonance in N = 82 nuclei
2010-01-01
In this study quasiparticle random-phase approximation with the translational invariant Hamiltonian using deformed mean field potential has been conducted to describe electric dipole excitations in 136Xe, 138Ba, 140Ce, 142Nd, 144Sm and 146Gd isotones. The distribution of the calculated E1 strength shows a resonance like structure at energies between 68 MeV exhausting up to 1% of the isovector electric dipole Energy Weighted Sum Rule and in some aspects nicely confirms the experimental data. It has been shown that the main part of E1 strength, observed below the threshold in these nuclei may be interpreted as main fragments of the Pygmy Dipole resonance. The agreement between calculated mean excitation energies as well as summed B(E1) value of the 1 excitations and the available exper...
2010-09-28
Strong coupling between a two-level system (TLS) and bosonic modes produces dramatic quantum optics effects. We consider a one-dimensional continuum of bosons coupled to a single localized TLS, a system which may be realized in a variety of plasmonic, photonic, or electronic contexts. We present the exact many-body scattering eigenstate obtained by imposing open boundary conditions. Multi-photon bound states appear in the scattering of two or more photons due to the coupling between the photons and the TLS. Such bound states are shown to have a large effect on scattering of both Fock and coherent state wavepackets, especially in the intermediate coupling strength regime. We compare the statistics of the transmitted light with a coherent state having the same mean photon number: as the interaction strength increases, the one-photon probability is suppressed rapidly, and the two- and three-photon probabilities are greatly enhanced due to the many-body bound states. This results in non-Poissonian light.
Generation of an electron-positron plasma in a magnetar magnetosphere
2008-01-01
We consider the electron-positron plasma generation processes in the magnetospheres of magnetars--neutron stars with strong surface magnetic fields, B0approx =1014-1015 G. We show that the photon splitting in a magnetic field, which is effective at large field strengths, does not lead to the suppression of plasma multiplication, but manifests itself in a high polarization of gamma-ray photons. A high magnetic field strength does not give rise to the second generation of particles produced by synchrotron photons. However, the density of the first-generation particles produced by curvature photons in the magnetospheres of magnetars can exceed the density of the same particles in the magnetospheres of ordinary radio pulsars. The plasma generation inefficiency can be attributed only to slow magnetar ...
BLAZAR HALOS AS PROBE FOR EXTRAGALACTIC MAGNETIC FIELDS AND MAXIMAL ACCELERATION ENERGY
2009-01-01
High-energy photons from blazars interact within tens of kpc with the extragalactic photon background, initiating electromagnetic pair cascades. The charged component of such cascades is deflected by extragalactic magnetic fields (EGMFs), leading to halos even around initially point-like sources. We calculate the intensity profile of the resulting secondary high-energy photons for different assumptions on the initial source spectrum and the strength of the EGMF, employing also fields found earlier in a constrained simulation of structure formation including magnetohydrodynamics processes. We find that the observation of halos around blazars like Mrk 180 probes an interesting range of EGMF strengths and acceleration models: in particular, blazar halos test if the photon energy spectrum at the source extends beyond approx100 TeV and how anisotropic ...
Study of Photon Strength Functions of Actinides: the case of U-235, Np-238 and Pu-241
The decay from excited levels in medium and heavy nuclei can be described in a statistical approach by means of Photon Strength Functions and Level Density distributions combined with the theory of the compound. The study of electromagnetic cascades following neutron capture by means of high efficiency detectors has been shown to be well suited for probing the properties of the Photon Strength Function of heavy (high level density) and/or radioactive (high background) nuclei. In this work we have investigated for the first time the validity of the recommended PSF for actinides, in particular 235U, 238Np and 241Pu. Our study includes the search for resonance structures in the PSF below Sn and draws conclusions regarding their existence and their characteristics in terms of energy, width and electromagnetic nature.
2010-01-01
The kinetics of photocatalytic degradation of multicomponent mixtures of four of the most powerful endocrine disrupting chemicals (estrogens) estrone (E1), 17b-estradiol (E2), 17a-ethynylestradiol (EE2) and estriol (E3) was studied in the presence and in the absence of TiO2 (Degussa P25) suspensions. Experiments were carried out with UVA and UVC radiation in a well characterized annular photoreactor. The results were analysed in terms of a simple first-order kinetic model, but including the explicit effect of photon absorption. This was accomplished by modelling the radiation field under heterogeneous (photocatalysis) conditions and by determining the spatial distribution of the local volumetric rate of photon absorption (LVRPA) in the reactor. The Six-Flux Absorption-Scattering Model (i.e...
Measurement of direct photon emission in the K(L) ---> pi+ pi- gamma decay mode
2006-04-01
In this paper the KTeV collaboration reports the analysis of 112.1 x 10{sup 3} candidate K{sub L} {yields} {pi}{sup +}{pi}{sup -}{gamma} decays including a background of 671 {+-} 41 events with the objective of determining the photon production mechanisms intrinsic to the decay process. These decays have been analyzed to extract the relative contributions of the Cp violating bremsstrahlung process and the CP conserving M1 and CP violating E1 direct photon emission processes. The M1 direct photon emission amplitude and its associated vector form factor parameterized as |{bar g}{sub M1}|(1 + a{sub 1}/a{sub 2}/(M{sub {rho}}{sup 2}-M{sub K}{sup 2}) + 2M{sub K}E{sub {gamma}}) have been measured to be |{bar g}{sub M1}| = 1.198 {+-} 0.035(stat) {+-} 0.086(syst) and a{sub 1}/a{sub 2} = =0.738 {+-} 0.007(stat) {+-} 0.018(syst) GeV{sup 2}/c{sup 2} respectively. An upper limit for the CP violating E1 direct emission amplitude |g{sub E1}| {le} 0.1 (90%CL) has been found. The overall ratio of direct photon emission (DE) to total photon emission including the bremsstrahlung process (IB) has been determined to be DE/(DE + IB) = 0.689 {+-} 0.021 for E{sub {gamma}} {ge} 20 MeV.
ON THE QUESTIONS OF THE NUCLEAR LEVEL DENSITY AND THE E1 PHOTON STRENGTH FUNCTIONS
1999-11-15
New results were derived from average level spacings of neutron resonances for the spin dispersion parameter of the nuclear level density, which demonstrated the influence of shell effects, as well as the interplay of nucleon pairing correlations for nuclei in the mass range from {sup 29}Si to {sup 241}Pu. The volume and surface components of the nuclear level density parameter, as well as the shell-damping factor, were determined as, a{sub v} = 0.076 {+-} 0.009 MeV{sup {minus}1} , a{sub s} = 0.180 {+-} 0.047 MeV{sup {minus}1}, and y{sub 0} = 0.047 {+-} 0.04 MeV{+-}, respectively. The effective nucleon mass at the Fermi surface is derived as m*/m = 1.09 {+-} 0.13. New evidence is presented for a dipole-quadrupole interaction term in the primary E1 transitions of average resonance capture data. This evidence is obtained by testing a proposed generalized Landau Fermi liquid model for spherical and deformed nuclei, which includes the effect of the dipole-quadrupole interaction. The Landau-Migdal interaction constant and the effective nucleon mass, are determined as F{sub 0}{prime} = 1.49 {+-} 0.08, and m*/m=1.04 {+-} 0.07, respectively.
2005-06-13
We report the discovery of very-high-energy (VHE) gamma-ray emission of the binary system PSR B1259-63/SS 2883 of a radio pulsar orbiting a massive, luminous Be star in a highly eccentric orbit. The observations around the 2004 periastron passage of the pulsar were performed with the four 13 m Cherenkov telescopes of the H.E.S.S. experiment, recently installed in Namibia and in full operation since December 2003. Between February and June 2004, a gamma-ray signal from the binary system was detected with a total significance above 13 sigma. The flux was found to vary significantly on timescales of days which makes PSR B1259-63 the first variable galactic source of VHE gamma-rays observed so far. Strong emission signals were observed in pre- and post-periastron phases with a flux minimum around periastron, followed by a gradual flux decrease in the months after. The measured time-averaged energy spectrum above a mean threshold energy of 380 GeV can be fitted by a simple power law F_0(E/1 TeV)^-Gamma with a photon index Gamma = 2.7+-0.2_stat+-0.2_sys and flux normalisation F_0 = (1.3+-0.1_stat+-0.3_sys) 10^-12 TeV^-1 cm^-2 s^-1. This detection of VHE gamma-rays provides unambiguous evidence for particle acceleration to multi-TeV energies in the binary system. In combination with coeval observations of the X-ray synchrotron emission by the RXTE and INTEGRAL instruments, and assuming the VHE gamma-ray emission to be produced by the inverse Compton mechanism, the magnetic field strength can be directly estimated to be of the order of 1 G.
Non-Markovian dynamics of a microcavity coupled to a waveguide in photonic crystals
2010-06-15
In this paper, the non-Markovian dynamics of a microcavity coupled to a waveguide in photonic crystals is studied based on Fano-type tight binding model. Using the exact master equation, we solve analytically and numerically the temporal evolution of the cavity coherent state and the associated physical observables. A critical transition is revealed when the coupling increase between the cavity and the waveguide. In particular, the cavity field becomes dissipationless when the coupling strength goes beyond a critical value, as a manifestation of strong non-Markovian memory effect. The result also indicates that the cavity can maintain in a coherent state with arbitrary small number of photons when it strongly couples to the waveguide at very low temperature. These properties can be measured experimentally through the photon current flowing over the waveguide in photonic crystals.
Lasing oscillation in a three-dimensional photonic crystal nanocavity with a complete bandgap
2010-06-10
We demonstrate lasing oscillation in a three-dimensional photonic crystal nanocavity. The laser is realized by coupling a cavity mode, which is localized in a complete photonic bandgap and exhibits the highest quality factor of ~38,500, with high-quality semiconductor quantum dots. We show a systematic change in the laser characteristics, including the threshold and the spontaneous emission coupling factor by controlling the crystal size, which consequently changes the strength of photon confinement in the third dimension. This opens up many interesting possibilities for realizing future ultimate light sources and three-dimensional integrated photonic circuits and for more fundamental studies of physics in the field of cavity quantum electrodynamics.
Lifetime measurements in nuclei with different shapes
1999-07-01
The thesis has sections on transition probabilities, experimental techniques and methods, near spherical and deformed nuclei and includes four specific papers with titles: 1) M1 transition strength in the odd-odd nucleus N=83 I 136. 2) Level lifetime in the four-proton nucleus Xe 136. 3) Enhanced and quenched B(E1) Transition rates between parity doublet bands in Ra 227- 4) Quenched E1 transition rates in Th 231.
Effective photon-photon interaction in a two-dimensional "photon fluid"
2003-09-15
We formulate an effective theory for the atom-mediated photon-photon interactions in a two-dimensional ``photon fluid'' confined in a Fabry-Perot resonator. With the atoms modelled by a collection of anharmonic Lorentz oscillators, the effective interaction is evaluated to second order in the coupling constant (the anharmonicity parameter). The interaction has the form of a renormalized two-dimensional delta-function potential, with the renormalization scale determined by the physical parameters of the system, such as density of atoms and the detuning of the photons relative to the resonance frequency of the atoms. For realistic values of the parameters, the perturbation series has to be resummed, and the effective interaction becomes independent of the ``bare'' strength of the anharmonic term. The resulting expression for the non-linear Kerr susceptibility, is parametrically equal to the one found earlier for a dilute gas of two-level atoms. Using our result for the effective interaction parameter, we derive conditions for the formation of a photon fluid, both for Rydberg atoms in a microwave cavity and for alkali atoms in an optical cavity.
Earth Science Technology Office (ESTO)
Cloud heights, planetary boundary layer, radiation balance ... Signal extraction technique may have application to other low signal strength applications, e.g. ... Each point is a single photon time of flight measurement to ...
Distribution of photon strength in nuclei by a method of two-step cascades
The applicability of sum-coincidence measurements of two-step cascade {gamma}-ray spectra to the determination of photon strength functions at intermediate {gamma}-ray energies (3 or 4 MeV) is discussed. An experiment based on thermal neutron capture in Nd was undertaken at the Brookhaven National Laboratory High Flux Beam Reactor to test this model. To understand the role of various uncertainties in similar experiments a series of model calculations was performed. We present an analysis of our experimental data which demonstrates the high sensitivity of the method to E1 and M1 photon strength functions. Our experimental data are in sharp contradiction to those expected from an E1 photon strength distributed according to the classical Lorentzian form with an energy invariant damping width. An alternative distribution of Kadmenskij et al., which violates Brink's Hypothesis, is strongly preferred. 13 refs., 5 figs.
Distribution of photon strength in nuclei by a method of two-step cascades
1990-01-01
The applicability of sum-coincidence measurements of two-step cascade {gamma}-ray spectra to the determination of photon strength functions at intermediate {gamma}-ray energies (3 or 4 MeV) is discussed. An experiment based on thermal neutron capture in Nd was undertaken at the Brookhaven National Laboratory High Flux Beam Reactor to test this model. To understand the role of various uncertainties in similar experiments a series of model calculations was performed. We present an analysis of our experimental data which demonstrates the high sensitivity of the method to E1 and M1 photon strength functions. Our experimental data are in sharp contradiction to those expected from an E1 photon strength distributed according to the classical Lorentzian form with an energy invariant damping width. An alternative distribution of Kadmenskij et al., which violates Brink's Hypothesis, is strongly preferred. 13 refs., 5 figs.
Source of coherent short wavelength radiation
An apparatus for producing coherent radiation ranging from X-rays to the far ultraviolet (i.e., 1 Kev to 10 eV) utilizing the Compton scattering effect. A photon beam from a laser is scattered on a high energy electron bunch from a pulse power linac. The short wavelength radiation produced by such scattering has sufficient intensity and spatial coherence for use in high resolution applications such as microscopy.
Lifetime of the Kpi=8- isomer in the neutron-rich nucleus 174Er, and N=106 E1 systematics
2009-01-01
Chopped-beam techniques and gamma-ray spectroscopy with Gammasphere have been used to measure the lifetime of the 1112-keV 8- isomeric state in 174Er. The value obtained of tau=5.8(4) s corresponds to a reduced hindrance of fnu=98 for the 163-keV E1 transition to the 8+ state of the ground-state band, in good agreement with the systematics of the corresponding E1 strengths in the N=106 isotones. The K-mixing in the 8- states is calculated in the context of the particle-rotor model and used to extract the underlying reduced hindrances
The energy dependence of the electric dipole strength in heavy nuclei
2008-10-13
On the basis of new photon scattering measurements and a reevaluation of average neutron resonance capture data we investigate how well Lorentzians adjusted to photo-neutron data in the giant dipole resonances give a good description of the photon strength also below the neutron threshold. If deformation effects are properly taken into account this is verified down to about 5 MeV for various nuclei with A>80 such that the previously employed differentiation between deformed and non-deformed nuclei is no longer necessary.
Reanalysis of the process of the cascade gamma decay of compound state of $^{198}$Au
2008-10-02
To further study the "pygmy" resonance phenomena in the photon strength function, we reanalyzed the two-step cascade data for the target nucleus $^{197}$Au using the Dubna group approach. The range of obtained values allows for meaningful conclusions: the level density at low excitation energy shows a step-like behavior; the electric dipole photon strength function has a broad maximum around $E_{\\gamma}=5$ MeV and is not typical of a "pygmy" resonance; the level density below $B_{n}$ also demonstrates step-like behavior.
Confining potential from interacting magnetic and torsion fields
2008-10-17
Adopting the gauge-invariant but path-dependent variables formalism, we study the coupling of torsion fields with photons in the presence of an external background electromagnetic. We explicitly show that, in the case of a constant electric field strength expectation value, the static potential remains Coulombic, while in the case of a constant magnetic field strength expectation value a confining potential is obtained. This result displays a marked qualitative departure from the usual coupling of axionlike particles with photons in the presence of an external magnetic field.
Two-photon decay in highly charged heavy ions: Spectral shape of the 2E1 (2 1S0 -
2009-01-01
We have measured the two-photon 2E1 transition from the singlet 1s2s 1S0 to the 1s21S0 ground state of helium-like tin. The experiment was performed by using initially Li-like tin ions in collision with a nitrogen gas target at the ESR storage ring at the energy of 300 MeV/u. The two-photon emission arises from the decay of the exclusively formed 1s2s states following the ionization of one K-shell electron from the Li-like ions. The obtained spectral shape of the 1s2s1S0 -
Spin squeezing in the presence of dissipation
2009-01-01
The transfer of spin between photons and localized atomic levels, for a chain of two-level atoms, is studied. The Hamiltonian of the system is modelled by a radiation term and by atom-atom and radiation-atom interactions. Effects due to dissipation are accounted for by atom-photon exchange-interactions of complex strength. It is found that the spin-squeezing is suppressed by dissipation. Calculations are performed for arrays of Rb atoms excited by a GaAlAs laser
Photothermal cathode measurements at the Advanced Photon Source
2006-01-01
The Advanced Photon Source (APS) ballistic bunch compression (BBC) gun in the Injector Test Stand (ITS) presently uses an M-type thermionic dispenser cathode as a photocathode. This photothermal cathode offers substantial advantages over conventional metal photocathodes, including easy replacement and easy cleaning via the cathode's built-in heater. We present the results of photoemission measurements as a function of cathode heater power, laser pulse energy, and applied rf field strength
Interferometry of direct photons in central $^{208}$Pb+$^{208}$Pb collisions at 158A GeV
Two-particle correlations of direct photons were measured in central /sup 208208/Pb+Pb collisions at 158A GeV. The invariant interferometric radii were extracted for 100<K/sub T/<300 MeV/c and compared to radii extracted from charged pion correlations. The yield of soft direct photons, K/sub T/<300 MeV/c, was extracted from the correlation strength and compared to theoretical calculations. (13 refs).
An Introduction to Multiphoton Ionization and Study of Ionization Rate of Hydrogen Atom
2009-01-01
From a semiclassical point of view, we discuss the problem of nonlinear interaction between electromagnetic radiation and atoms. The time-dependent Schroedinger equation for single electron systems is solved using perturbative technique to obtain transition probability. We also discuss higher order perturbation used in multiple processes where two or more quanta are emitted instead of a single photon. The approach is based on the assumption that the perturbation is small. From the transition probability ionization rate and absorption, the cross-section of hydrogen atoms is calculated. Variation in photon energy and field strength is analyzed. Variation of cross-section with photon energy is discussed
Evolution of the pygmy dipole resonance in nuclei with neutron excess
2009-06-26
The electric dipole excitation of various nuclei is calculated with a Random Phase Approximation phenomenological approach. The evolution of the strength distribution in various groups of isotopes, oxygen, calcium, zirconium and tin, is studied. The neutron excess produces $E1$ strength in the low energy region. Indexes to measure the collectivity of the excitation are defined. We studied the behavior of proton and neutron transition densities to determine the isoscalar or isovector nature of the excitation. We observed that in medium-heavy nuclei the low-energy $E1$ excitation has characteristics rather different that those exhibited by the giant dipole resonance. This new type of excitation can be identified as pygmy dipole resonance.
Allowed and forbidden transition parameters for Fe XV
2009-01-01
A comprehensive set of fine structure energy levels, oscillator strengths (f), line strengths (S), and radiative decay rates (A) for bound-bound transitions in Fe XV is presented. The allowed electric dipole (E1) transitions were obtained from the relativistic Breit-Pauli R-matrix method which is based on the close coupling approximation. A total of 507 fine structure energy levels with n yield a total of 27,812 E1, same-spin multiplets and intercombination transitions. The A values are in good agreement with those compiled by NIST and other existing values for most transitions. Forbidden transitions are obtained from a set of 20 configurations with orbitals ranging from 1s to 5f using the relativistic code ...
Allowed and forbidden transition parameters for Fe XV
2009-01-01
A comprehensive set of fine structure energy levels, oscillator strengths (f), line strengths (S), and radiative decay rates (A) for bound-bound transitions in Fe XV is presented. The allowed electric dipole (E1) transitions were obtained from the relativistic Breit-Pauli R-matrix method which is based on the close coupling approximation. A total of 507 fine structure energy levels with n10, l9, and 0J10 are found. They agree within 1% with the available observed energies. These energy levels yield a total of 27,812 E1, same-spin multiplets and intercombination transitions. The A values are in good agreement with those compiled by NIST and other existing values for most transitions. Forbidden transitions are obtained from a set of 20 configurations with orbitals ranging from 1s to 5f using...
Excitation energy and strength of the pygmy dipole resonance in stable tin isotopes
2009-01-19
The $^{112,120}$Sn$(\\gamma,\\gamma')$ reactions have been studied at the S-DALINAC. Electric dipole (E1) strength distributions have been determined including contributions from unresolved strength extracted by a fluctuation analysis. Together with available data on $^{116,124}$Sn, an experimental systematics of the pygmy dipole resonance (PDR) in stable even-mass tin isotopes is established. The PDR centroid excitation energies and summed strengths are in reasonable agreement with quasiparticle-phonon model calculations based on a nonrelativistic description of the mean field but disagree with relativistic quasiparticle random-phase approximation predictions.
Photon strength distributions in stable even-even molybdenum isotopes
2007-07-27
Electromagnetic dipole-strength distributions up to the particle separation energies are studied for the stable even-even nuclides $^{92,94,96,98,100}$Mo in photon scattering experiments at the superconducting electron accelerator ELBE of the Forschungszentrum Dresden-Rossendorf. The influence of inelastic transitions to low-lying excited states has been corrected by a simulation of $\\gamma$ cascades using a statistical model. After corrections for branching ratios of ground-state transitions, the photon-scattering cross-sections smoothly connect to data obtained from $(\\gamma,n)$-reactions. With the newly determined electromagnetic dipole response of nuclei well below the particle separation energies the parametrisation of the isovector giant-dipole resonance is done with improved precision.
Effect of a chameleon scalar field on the cosmic microwave background
2009-01-01
We show that a direct coupling between a chameleonlike scalar field and photons can give rise to a modified Sunyaev-Zel'dovich (SZ) effect in the cosmic microwave background (CMB). The coupling induces a mixing between chameleon particles and the CMB photons when they pass through the magnetic field of a galaxy cluster. Both the intensity and the polarization of the radiation are modified. The degree of modification depends strongly on the properties of the galaxy cluster such as magnetic field strength and electron number density. Existing SZ measurements of the Coma cluster enable us to place constraints on the photon-chameleon coupling. The constrained conversion probability in the cluster is PComa(204 GHz)-5 at 95% confidence, corresponding to an upper bound on the coupling strength of ...
An experiment is described which studied quantum electrodynamic interactions under conditions of extremely high fields, along with a review of the relevant theory. The high fields were created by an intense, tightly-focused pulse of laser light at green or infrared wavelengths, into which was sent an ultra-relativistic electron beam of 46.6-GeV energy. The relevant theory is that of an electron in an electromagnetic wave so intense that the electron's mass is effectively shifted by the transverse momentum imparted to it by the wave, and the electron encounters field strengths comparable to the Schwinger critical field strength of 511 kV per Compton wavelength. An electron in the intense wave may radiate a photon and balance 4- momentum by absorbing multiple photons from the laser, which can lead to real photons with energies above the kinematic limit for conventional Compton scattering....
Quantum interference of biphotons at a blazed grating
2009-03-17
Correlations between photons are interesting for a number of applications and concepts in metrology in particular for resolution improvements in different methods of quantum imaging. Since Fock-states of N-photons of wavelength lambda in interference schemes acquire N-times the phase shift of single photons these states can appear as if they had a de Broglie wavelength of lambda/N. A biphoton beam diffracted at a blazed grating shows this reduced de Broglie wavelength. This experiment can be seen as a purification of biphotons of a certain correlation strength on the one hand. On the other hand the evaluation of the one-photon and two-photon rate distributions in the Fraunhofer far field of the grating allows for an analysis of the spatial correlation between the photons. An experimental demonstration of these ideas tested for a biphoton beam generated by parametric down conversion (PDC) is reported. We demonstrate in addition that the existence of higher order spatial modes is important to observe strong spatial correlations and to observe the photonic de Broglie wavelength of lambda/2 for biphotons.
Complementarity in variable strength quantum non-demolition measurements
2009-09-15
Using a linear optic quantum gate we perform a variable strength quantum non-demolition measurement, to elucidate the role of which-path knowledge in a complementarity experiment. Specifically, we demonstrate that the entanglement created by the measurement interaction prevents an exhaustive description in terms of complementary wave-like and particle-like behaviour of a single photon in an interferometer.
Complementarity in variable strength quantum non-demolition measurements
2009-01-01
Using a linear optic quantum gate we perform a variable strength quantum non-demolition measurement, to elucidate the role of which-path knowledge in a complementarity experiment. Specifically, we demonstrate that the entanglement created by the measurement interaction prevents an exhaustive description in terms of complementary wave-like and particle-like behaviour of a single photon in an interferometer
Search for low lying dipole strength in the neutron rich nucleus $^{26}$Ne
2007-05-23
Coulomb excitation of the exotic neutron-rich nucleus $^{26}$Ne on a $^{nat}$Pb target was measured at 58 A.MeV in order to search for low-lying E1 strength above the neutron emission threshold. Data were also taken on an $^{nat}$Al target to estimate the nuclear contribution. The radioactive beam was produced by fragmentation of a 95 A.MeV $^{40}$Ar beam delivered by the RIKEN Research Facility. The set-up included a NaI gamma-ray array, a charged fragment hodoscope and a neutron wall. Using the invariant mass method in the $^{25}$Ne+n channel, we observe a sizable amount of E1 strength between 6 and 10 MeV. The reconstructed $^{26}$Ne angular distribution confirms its E1 nature. A reduced dipole transition probability of B(E1)=0.49$\\pm$0.16 $e^2fm^2$ is deduced. For the first time, the decay pattern of low-lying strength in a neutron-rich nucleus is obtained. The results are discussed in terms of a pygmy resonance centered around 9 MeV.
Resolving photon number states in a superconducting circuit
2006-08-30
Electromagnetic signals are always composed of photons, though in the circuit domain those signals are carried as voltages and currents on wires, and the discreteness of the photon's energy is usually not evident. However, by coupling a superconducting qubit to signals on a microwave transmission line, it is possible to construct an integrated circuit where the presence or absence of even a single photon can have a dramatic effect. This system is called circuit quantum electrodynamics (QED) because it is the circuit equivalent of the atom-photon interaction in cavity QED. Previously, circuit QED devices were shown to reach the resonant strong coupling regime, where a single qubit can absorb and re-emit a single photon many times. Here, we report a circuit QED experiment which achieves the strong dispersive limit, a new regime of cavity QED in which a single photon has a large effect on the qubit or atom without ever being absorbed. The hallmark of this strong dispersive regime is that the qubit transition can be resolved into a separate spectral line for each photon number state of the microwave field. The strength of each line is a measure of the probability to find the corresponding photon number in the cavity. This effect has been used to distinguish between coherent and thermal fields and could be used to create a photon statistics analyzer. Since no photons are absorbed by this process, one should be able to generate non-classical states of light by measurement and perform qubit-photon conditional logic, the basis of a logic bus for a quantum computer.
Characterization of multiple-photon absorption and dissociation of polyatomic molecules
A quantitative comparison of multiple-photon absorption (MPA) and dissociation (MPD) has been performed for experiments with a number of different polyatomic molecules. Appropriate normalization techniques for the absorption and dissociation parameters are formulated to account for the different conditions of the experiment and the molecular parameters. This procedure in a first approximation, accounts for the effects of independent variables such as gas pressure, optical bandwidth, optical pulse duration, excitation frequency, spectral width of the optical absorption band, absorption strength of the transition, bond strength, and the density of states in the molecule. The theoretical description of the dynamics of the absorbing ground state is considered and used to provide the rationale for the normalization procedure. The results of this analysis indicate that the functional dependence of the number of photons absorbed per molecule with fluence is qualitatively the same for the most molecules. Similarly, the probability for dissociation of most molecules can be related to the density of vibrational states, the bond strength, the number of photons absorbed per molecule, and the width of the absorbing transition. The functional relationships derived for MPA and MPD can be related to several theoretical aspects of the optical interaction process. In particular, the implications for the basic absorption mechanisms and the distribution of vibrational energy in the molecule will be addressed.
Characterization of multiple-photon absorption and dissociation of polyatomic molecules
1980-01-01
A quantitative comparison of multiple-photon absorption (MPA) and dissociation (MPD) has been performed for experiments with a number of different polyatomic molecules. Appropriate normalization techniques for the absorption and dissociation parameters are formulated to account for the different conditions of the experiment and the molecular parameters. This procedure in a first approximation, accounts for the effects of independent variables such as gas pressure, optical bandwidth, optical pulse duration, excitation frequency, spectral width of the optical absorption band, absorption strength of the transition, bond strength, and the density of states in the molecule. The theoretical description of the dynamics of the absorbing ground state is considered and used to provide the rationale for the normalization procedure. The results of this analysis indicate that the functional dependence of the number of photons absorbed per molecule with fluence is qualitatively the same for the most molecules. Similarly, the probability for dissociation of most molecules can be related to the density of vibrational states, the bond strength, the number of photons absorbed per molecule, and the width of the absorbing transition. The functional relationships derived for MPA and MPD can be related to several theoretical aspects of the optical interaction process. In particular, the implications for the basic absorption mechanisms and the distribution of vibrational energy in the molecule will be addressed.
2009-01-01
We present, in this work, Doppler-free two-photon optogalvanic spectroscopy as a tool to measure the electric field strength in the cathode fall region of a hollow cathode discharge via the Stark splitting of the 2S level of atomic deuterium. The strong electric field strength (1 to 4 kV cm-1) present in the hollow cathode is determined for various discharge conditions (currents from 50 to 200 mA and pressures from 400 to 1350 Pa), which allows investigation of the corresponding variations of the cathode fall and its changes with discharge operation time
2009-01-01
Dipole-strength distributions in the stable even-mass molybdenum isotopes up to the neutron-separation energies have been studied in photon-scattering experiments with bremsstrahlung at the superconducting electron accelerator ELBE at the Research Center Dresden-Rossendorf, Germany, and with mono-energetic photon beams at the High Intensity Gamma-ray Source facility at Triangle Universities Nuclear Laboratory. In order to determine the dipole-strength distribution, statistical methods were developed for the analysis of the measured spectra. The data obtained for the stable even-mass molybdenum isotopes from the present (gamma,gamma') experiments are combined with (gamma,n) cross sections from the literature resulting in a photoabsorption cross section covering the full range from about 4 to 15 MeV, which is of ...
Dipole strength in 144Sm studied via (gamma,n), (gamma,p) and (gamma,alpha) reactions
2010-05-13
Photoactivation measurements on 144Sm have been performed with bremsstrahlung endpoint energies from 10.0 to 15.5 MeV at the bremsstrahlung facility of the superconducting electron accelerator ELBE of Forschungszentrum Dresden-Rossendorf. The measured activation yield for the 144Sm(gamma,n) reaction is compared with the calculated yield using cross sections from previous photoneutron experiments. The activation yields measured for all disintegration channels 144Sm(gamma,n), (gamma,p) and (gamma,alpha) are compared to the yield calculated by using Hauser-Feshbach statistical models. A new parametrization of the photon strength function is presented and the yield simulated by using the modified photon strength parameters are compared to the experimental data.
2002-11-13
We present a theoretical study of radiative transfer in strongly magnetized electron-ion plasmas, focusing on the effect of vacuum polarization due to quantum electrodynamics. This study is directly relevant to thermal radiation from the surfaces of highly magnetized neutron stars, which have been detected in recent years. Strong-field vacuum polarization modifies the photon propagation modes in the plasma, and induces a ``vacuum resonance'' at which a polarized X-ray photon propagating outward in the neutron star atmosphere can convert from a low-opacity mode to a high-opacity mode and vice versa. The effectiveness of this mode conversion depends on the photon energy and the atmosphere density gradient. For a wide range of field strengths, $7\\times 10^{13}< B < 10^{16}$ G, the vacuum resonance lies between the photospheres of the two photon modes, and the emergent radiation spectrum from the neutron star is significantly modified by the vacuum resonance. (For lower field strengths, only the polarization spectrum is affected.) Under certain conditions, which depend on the field strength, photon energy and propagation direction, the vacuum resonance is accompanied by the phenomenon of mode collapse (at which the two photon modes become degenerate) and the breakdown of Faraday depolarization. Thus, the widely used description of radiative transfer based on photon modes is not adequate to treat the vacuum polarization effect rigorously. We study the evolution of polarized X-rays across the vacuum resonance and derive the transfer equation for the photon intensity matrix (Stokes parameters), taking into account the effect of birefringence of the plasma-vacuum medium, free-free absorption, and scatterings by electrons and ions.
Mechanisms of the ultrasonic modulation of fluorescence in turbid media
2008-11-15
Full Text Available.To understand the modulation mechanisms of fluorescence emission induced by ultrasonic waves in turbid media, a mathematical model is proposed and compared with the recent experimental observations of Kobayashi et al. [Appl. Phys. Lett. 89, 181102 (2006)]. Modulation of fluorophore concentration is considered as the source of the oscillation of fluorescence signals when fluorophore concentration is low enough so that quenching effects can be ignored. By solving the rate equation and photon diffusion equation, quantitative solutions are given to quantify the modulation strength. Our calculations predict that the modulation depth (the ratio of the modulated signal strength to the unmodulated signal strength) can reach 10
Quantum non-demolition measurement of microwave photons using engineered quadratic interactions
2010-08-20
We present a quantum electrical circuit with Josephson junctions formed of two anharmonic oscillators coupled with an interaction $g\\gamma_{1}^{2}\\gamma_{2}^{2}$ where $\\gamma_{1}$ and $\\gamma_{2}$ are position-like coordinates. This type of coupling allows the quantum non-demolition measurement of the energy of one oscillator by monitoring the frequency of the second oscillator. Despite the fundamental tradeoff between the coupling strength $g$ and maximum photon storage capacity of the oscillators, it is possible to achieve high fidelity detection of up to 10 photons over time scale of the order of microseconds. We discuss the possibility of observing quantum jumps in the number of photons and related applications.
Polariton optics of semiconductor photonic dots: weak and strong coupling limits
2004-01-01
We develop coherent optics of dipole-active, dispersionless excitons in spherical semiconductor photonic dots (PDs). In the absence of any incoherent scattering, both the strong and weak coupling regimes can intrinsically be realized simply by changing the parameters of the dot and surrounding medium. A criterion, which attributes the transition between these two regimes to a discrete topological change of the relevant dispersion curves, is found and approximated by an analytic expression. The transition depends upon the intrinsic radiative lifetime of the PD photon eigenstates, i.e. it is determined by the parameters of the structure (the oscillator strength of the exciton-photon interaction, PD radius and the ratio of the background dielectric constants inside and outside of the dot). We propose the use of high-precision modulation spectroscopy in order to ...
Photon-stimulated production of electron-positron pairs in electric field
2009-10-27
The rate of $e^+e^-$ pair creation by external electric field in the presence of an incident photon beam is calculated for the photon energy far below the threshold, $\\omega \\ll m$, and the field strength small as compared to the critical one, $e E \\ll m^2$. We find the pair production rate using a recently developed method based on calculation of the process in a thermal bath with subsequent identification of the contribution of single-photon states. We demonstrate that a non-trivial dependence on the ratio of the small parameters, $\\omega m/(e E)$, emerges in this approach from an essentially (semi)classical calculation.
Photon scattering experiment on 139La below neutron separation energy at ELBE
2009-01-01
Gamma strength function is the important input parameter to determine the photodisintegration rate and neutron capture rate for astrophysics and nuclear technologies. To test the model calculation, photon-scattering cross sections were measured for 139La up to the neutron separation energy with bremsstrahlung at an electron kinetic energy of 11.5 MeV. Scattered photons were measured with four 100% HPGe detectors, and 11B is used to determine the gamma flux. The experimental data was analyzed with statistical methods to obtain the intensities of the ground-state transitions and their branching ratios. The present 139La photon scattering cross sections are combined with 139La photoneutron cross sections
2008-01-01
Microphotoluminescence measurements on InAs/GaAs quantum rings embedded in a bi-dimensional photonic crystal cavity display enhanced emission intensity of single rings depending on the coupling strength to the cavity modes. The cavity is formed by three holes missing at the center of the photonic crystal structure (a linear 3 defect, L3). Light emission by the quantum rings show sharp lines at low excitation power. They undergo different enhancement factors by the separate effects of the photonic crystal and by coupling to the resonant modes, which show full linear polarization. Upon changing temperature, the uncoupled emission of single quantum rings and the resonant modes undergo different frequency shifts. This allows for an external control of the coupling.
Mechanism of photonic band gap, optical properties, tuning and applications
2006-01-01
Mechanism of occurrence of Photonic Band Gap (PBG) is presented for 3-D structure using close packed face centered cubic lattice. Concepts and our work, specifically optical properties of 3-D photonic crystal, relative width, filling fraction, effective refractive index, alternative mechanism of photonic band gap scattering strength and dielectric contrast, effect of fluctuations and minimum refractive index contrast, are reported. The temperature tuning and anisotropy of nematic and ferroelectric liquid crystal infiltrated opal for different phase transitions are given. Effective dielectric constant with filling fraction using Maxwell Garnet theory (MG), multiple modified Maxwell Garnet (MMMG) and Effective Medium theory (EM) and results are compared with experiment to understand the occurrence of PBG. Our calculations of Lamb shifts including ...
2009-08-24
Mirror dark matter provides a simple framework for which to explain the DAMA/LIBRA annual modulation signal consistently with the null results of the other direct detection experiments. The simplest possibility involves ordinary matter interacting with mirror dark matter via photon-mirror photon kinetic mixing of strength {epsilon}{approx}10{sup -9}. We confirm that photon-mirror photon mixing of this magnitude is consistent with constraints from ordinary Big Bang nucleosynthesis as well as the more stringent constraints from cosmic microwave background measurements and large scale structure considerations.
Direct gamma and gamma-jet measurement capability of ATLAS for Pb+Pb collisions
2009-01-01
The ATLAS detector at the LHC is capable of efficiently separating photons and neutral hadrons based on their shower shapes over a wide range in eta, phi, and ET, either in addition to or instead of isolation cuts. This provides ATLAS with a unique strength for direct photon and gamma-jet physics as well as access to the unique capability to measure non-isolated photons from fragmentation or from the medium. We present a first look at the ATLAS direct photon measurement capabilities in Pb+Pb and, for reference, p+p collisions at sq root(sNN)=5.5TeV over the region |eta|
Direct $\\gamma$ and $\\gamma$-jet measurement capability of ATLAS for Pb+Pb collisions
The ATLAS detector at the LHC is capable of efficiently separating photons and neutral hadrons based on their shower shapes over a wide range in eta, phi, ET, either in addition to or instead of isolation cuts. This provides ATLAS with a unique strength for direct photon and gamma-jet physics as well as access to the unique capability to measure non-isolated photons from fragmentation or from the medium. We present a first look at the ATLAS direct photon measurement capabilities in Pb+Pb and, for reference, p+p collisions at sqrt(sNN)=5.5 TeV over the region |eta|<2.4.
Constraining resonant photon-axion conversions in the Early Universe
2009-05-15
The presence of a primordial magnetic field would have induced resonant conversions between photons and axion-like particles (ALPs) during the thermal history of the Universe. These conversions would have distorted the blackbody spectrum of the cosmic microwave background (CMB). In this context, we derive bounds on the photon-ALP resonant conversions using the high precision CMB spectral data collected by the FIRAS instrument on board of the Cosmic Background Explorer. We obtain upper limits on the product of the photon-ALP coupling constant g times the magnetic field strength B down to gB<or similar 10{sup -13} GeV{sup -1} nG for ALP masses below the eV scale. (orig.)
Constraining resonant photon-axion conversions in the Early Universe
2009-06-01
The presence of a primordial magnetic field would have induced resonant conversions between photons and axion-like particles (ALPs) during the thermal history of the Universe. These conversions would have distorted the blackbody spectrum of the cosmic microwave background (CMB). In this context, we derive bounds on the photon-ALP resonant conversions using the high precision CMB spectral data collected by the FIRAS instrument on board of the Cosmic Background Explorer. We obtain upper limits on the product of the photon-ALP coupling constant g times the magnetic field strength B down to g B > 10^{-13} GeV^{-1} nG for ALP masses below the eV scale.
Lifetime measurements and calculated transition probabilities in W III
2008-01-01
New experimental lifetimes for two levels in doubly ionized tungsten, W III, have been obtained using the time-resolved laser-induced-fluorescence technique. Theoretical oscillator strengths obtained from a HFR calculation including the effects of core-polarization are reported for all transitions from levels below E-1 and with log gf
Wouthuysen-Field coupling strength and application to high-redshift 21 cm radiation
2005-07-05
The first UV sources in the universe are expected to have coupled the HI spin temperature to the gas kinetic temperature via scattering in the Lyman-alpha resonance [the Wouthuysen-Field (WF) effect]. By establishing an HI spin temperature different from the temperature of the CMB, the WF effect should allow observations of HI during the reionization epoch in the redshifted 21 cm line. This paper investigates four mechanisms that can affect the strength of the WF effect that were not previously considered: (1) Photons redshifting into the HI Lyman resonances may excite an H atom and result in a radiative cascade terminating in two-photon 2s->1s emission, rather than always degrading to Lyman-alpha as usually assumed. (2) The fine structure of the Lyman-alpha resonance alters the photon frequency distribution and leads to a suppression of the scattering rate. (3) The spin-flip scatterings change the frequency of the photon and cause the photon spectrum to relax not to the kinetic temperature of the gas but to a temperature between the kinetic and spin temperatures, effectively reducing the strength of the Wouthuysen-Field coupling. (4) Near line centre, a photon can change its frequency by several times the line width in a single scattering event, thus potentially invalidating the usual calculation of the Lyman-alpha spectral distortion based on the diffusion approximation. It is shown that (1) suppresses the WF coupling strength by a factor of up to ~2, while (2) and (3) are important only at low kinetic temperatures. Effect (4) has a =2K. If the pre-reionization IGM was efficiently heated by X-rays, only effect (1) is important. Fitting formulae are provided for the range of T_k>=2K and Gunn-Peterson optical depth 10^5--10^7. [ABRIDGED]
Spin- and time-resolved photoemission studies of thin Co2FeSi Heusler alloy films
2006-05-31
We have studied the possibly half metallic Co2FeSi full Heusler alloy by means of spin- and time-resolved photoemission spectroscopy. For excitation, the second and fourth harmonic of femtosecond Ti:sapphire lasers were used, with photon energies of 3.1 eV and 5.9 eV, respectively. We compare the dependence of the measured surface spin polarization on the particular photoemission mechanism, i.e. 1-photon-photoemission (1PPE) or 2-photon photoemission (2PPE). The observed differences in the spin polarization can be explained by a spin-dependent lifetime effect occurring in the 2-photon absorption process. The difference in escape depth of the two methods in this context suggests that the observed reduction of spin polarization (compared to the bulk) cannot be attributed just to the outermost surface layer but takes place at least 4-6 nm away from the surface.
gamma-strength functions in 60Ni from two-step cascades following proton capture
2010-01-01
The two-step cascade method previously used in neutron-capture experiments is now applied to a proton-capture reaction. The spectrum of two-step cascades populating the first 2+ level of 60Ni has been measured with the 59Co(p,2gamma)60Ni reaction. The simulation technique used for the spectrum analysis allows one to reveal the range of possible shapes of both E1 and M1 gamma-strength functions. The low-energy enhancement previously observed in 3He-induced reactions is seen to appear in M1 strength functions of 60Ni
Gamma-strength functions in 60Ni from two-step cascades following proton capture
2009-11-11
The two-step cascade method previously used in neutron capture experiments is now applied to a proton capture reaction. The spectrum of two-step cascades populating the first 2+ level of 60Ni has been measured with 59Co(p,2gamma)60Ni reaction. The simulation technique used for the spectrum analysis allows one to reveal the range of possible shapes of both E1 and M1 gamma-strength functions. The low-energy enhancement previously observed in 3He induced reactions is seen to appear in M1 strength functions of 60Ni.
Dipole responses in Nd and Sm isotopes with shape transitions
2010-08-10
Photoabsorption cross sections of Nd and Sm isotopes from spherical to deformed even nuclei are systematically investigated by means of the quasiparticle-random-phase approximation based on the Hartree-Fock-Bogoliubov ground states (HFB+QRPA) using the Skyrme energy density functional. The gradual onset of deformation in the ground states as increasing the neutron number leads to characteristic features of the shape phase transition. The calculation well reproduce the isotopic dependence of broadening and emergence of a double-peak structure in the cross sections without any adjustable parameter. We also find that the deformation plays a significant role for low-energy dipole strengths. The $E1$ strengths are fragmented and considerably lowered in energy. The summed $E1$ strength up to 10 MeV is enhanced by a factor of five or more.
Search for low lying dipole strength in the neutron rich nucleus 26Ne
2007-01-01
Coulomb excitation of the exotic neutron-rich nucleus 26Ne on a natPb target was measured at 58 A.MeV in order to search for low-lying E1 strength above the neutron emission threshold. Data were also taken on an natAl target to estimate the nuclear contribution. The radioactive beam was produced by fragmentation of a 95 A.MeV 40Ar beam delivered by the RIKEN Research Facility. The set-up included a NaI gamma-ray array, a charged fragment hodoscope and a neutron wall. Using the invariant mass method in the 25Ne+n channel, we observe a sizable amount of E1 strength between 6 and 10 MeV. The reconstructed 26Ne angular distribution confirms its E1 nature. A reduced dipole transition probability of B(E1)=0.49+/-0.16 e2fm2 is deduced. For the first time, the decay pattern of ...
Electric dipole strength distribution below the E1 giant resonance in N = 82 nuclei
In this study quasiparticle random-phase approximation with the translational invariant Hamiltonian using deformed mean field potential has been conducted to describe electric dipole excitations in 136Xe, 138Ba, 140Ce, 142Nd, 144Sm and 146Gd isotones. The distribution of the calculated E1 strength shows a resonance like structure at energies between 6-8 MeV exhausting up to 1% of the isovector electric dipole Energy Weighted Sum Rule and in some aspects nicely confirms the experimental data. It has been shown that the main part of E1 strength, observed below the threshold in these nuclei may be interpreted as main fragments of the Pygmy Dipole resonance. The agreement between calculated mean excitation energies as well as summed B( E1) value of the 1? excitations and the available experimental data is quite good. The calculations indicate the presence of a few prominent positive parity 1+ States in heavy N = 82 isotones in the energy interval 6-8 MeV which shows not all dipole excitations were of electric character in this energy range.
Measurement of Atomic Oscillator Strength Distribution from the Excited States
Saturation technique has been employed to measure the oscillator strength distribution in spectra of helium lithium using an electrical discharge cell a thermionic diode ion detector respectively. The photoabsorption cross sections in the discrete or bound region (commonly known as f-values) have been determined form the Rydberg series accessed from a particular excited state calibrating it with the absolute value of the photoionization cross section measured at the ionization threshold. The extracted discrete f-values merge into the oscillator strength densities, estimated from the measured photoionization cross sections at different photon energies above the first ionization threshold. The experimental data on helium and lithium show continuity between the discrete and the continuous oscillator strengths across the ionization threshold.
Improved Bar Impact Tests Using A Photonic Doppler Velocimeter
2009-01-01
Bar impact tests, using the techniques described elsewhere in this symposium, were used to measure compressive and tensile strengths of borosilicate glass, soda lime glass, and a glass ceramic. The glass ceramic was 25% crystalline spinel, furnished by Corning Inc. There are two measures of compressive strength: the peak stress that can be transmitted in unconfined compression, and the 'steady state' strength. For borosilicate glass and soda lime glass, these values were similar, being about 1.8 and 1.5 GPa, respectively. The glass ceramic (25% spinel) was almost 50% stronger. Tensile failure in the glass and glass ceramic takes places via surface flaws, and thus tensile strength is an extrinsic, as opposed to intrinsic property
IMPROVED BAR IMPACT TESTS USING A PHOTONIC DOPPLER VELOCIMETER
Bar impact tests, using the techniques described elsewhere in this symposium, were used to measure compressive and tensile strengths of borosilicate glass, soda lime glass, and a glass ceramic. The glass ceramic was 25% crystalline spinel, furnished by Corning Inc. There are two measures of compressive strength: the peak stress that can be transmitted in unconfined compression, and the 'steady state' strength. For borosilicate glass and soda lime glass, these values were similar, being about 1.8 and 1.5 GPa, respectively. The glass ceramic (25% spinel) was almost 50% stronger. Tensile failure in the glass and glass ceramic takes places via surface flaws, and thus tensile strength is an extrinsic, as opposed to intrinsic property.
IMPROVED BAR IMPACT TESTS USING A PHOTONIC DOPPLER VELOCIMETER
2009-08-24
Bar impact tests, using the techniques described elsewhere in this symposium, were used to measure compressive and tensile strengths of borosilicate glass, soda lime glass, and a glass ceramic. The glass ceramic was 25% crystalline spinel, furnished by Corning Inc. There are two measures of compressive strength: the peak stress that can be transmitted in unconfined compression, and the 'steady state' strength. For borosilicate glass and soda lime glass, these values were similar, being about 1.8 and 1.5 GPa, respectively. The glass ceramic (25% spinel) was almost 50% stronger. Tensile failure in the glass and glass ceramic takes places via surface flaws, and thus tensile strength is an extrinsic, as opposed to intrinsic property.
IMPROVED BAR IMPACT TESTS USING A PHOTONIC DOPPLER VELOCIMETER
2009-01-01
Bar impact tests, using the techniques described elsewhere in this symposium, were used to measure compressive and tensile strengths of borosilicate glass, soda lime glass, and a glass ceramic. The glass ceramic was 25% crystalline spinel, furnished by Corning Inc. There are two measures of compressive strength: the peak stress that can be transmitted in unconfined compression, and the 'steady state' strength. For borosilicate glass and soda lime glass, these values were similar, being about 1.8 and 1.5 GPa, respectively. The glass ceramic (25% spinel) was almost 50% stronger. Tensile failure in the glass and glass ceramic takes places via surface flaws, and thus tensile strength is an extrinsic, as opposed to intrinsic property
The problem of determining the contribution of the exciton--photon coupling to the absorption line shape or width of an exciton is addressed. In this regard, both the spatially homogeneous (polariton) and inhomogeneous wave models are considered. For the latter model, the theory is complex although a line shape expression is derived for the case of high exciton velocity and low oscillator strength. The related problem of determining the conditions under which the strong exciton--photon coupling limit is attained is also discussed. It is in this limit that light attenuation is independent of the oscillator strength. The theory plus new experimental data on the a exciton of naphthalene argue for the inadequacy of the polariton model. On the other hand, reasonable agreement between the data and the spatially inhomogeneous wave theory developed here is obtained. Thus, it is possible to estimate that the exciton--photon coupling contribution to the a-exciton linewidth is 0.26 cm/sup -1/. This is the major portion of the 2 K linewidth of 0.3 cm/sup -1/.
1978-12-15
The problem of determining the contribution of the exciton--photon coupling to the absorption line shape or width of an exciton is addressed. In this regard, both the spatially homogeneous (polariton) and inhomogeneous wave models are considered. For the latter model, the theory is complex although a line shape expression is derived for the case of high exciton velocity and low oscillator strength. The related problem of determining the conditions under which the strong exciton--photon coupling limit is attained is also discussed. It is in this limit that light attenuation is independent of the oscillator strength. The theory plus new experimental data on the a exciton of naphthalene argue for the inadequacy of the polariton model. On the other hand, reasonable agreement between the data and the spatially inhomogeneous wave theory developed here is obtained. Thus, it is possible to estimate that the exciton--photon coupling contribution to the a-exciton linewidth is 0.26 cm/sup -1/. This is the major portion of the 2 K linewidth of 0.3 cm/sup -1/.
2004-10-29
Directed and elliptic flow of inclusive photons near mid-rapidity in $158 $A GeV Pb+Pb collisions has been studied. The data have been obtained with the photon spectrometer LEDA of the WA98 experiment at the CERN SPS. The flow strength has been measured for various centralities as a function of $p_T$ and rapidity over $0.18 < p_T < 1.5 \\mathrm{GeV}/c$ and $2.3 < y < 2.9$. The angular anisotropy has been studied relative to an event plane obtained in the target fragmentation region that shows the elliptic flow to be in-plane. The elliptic flow has also been studied using two-particle correlations and shown to give similar results. A small directed flow component is observed. Both the directed and elliptic flow strengths increase with $p_T$. The photon flow results are used to estimate the corresponding neutral pion flow.
Nuclear Molecular Halo$$bThreshold Effect or Soft Dipole in $^{11}Li$?
The observation of large E1 strength near threshold in the electromagnetic dissociation of 11Li poses a fundamental question: Is the large E1 strength due to the threshold or is it due to a low lying E1 state? Such molecular cluster states were observed in 18O and in several nuclei near the drip line. We discuss the nature of the "threshold effect" as well as review the situation in Molecular (and Particle Physics) where such Molecular States are observed near the dissociation limit. We suggest that the situation in 11Li is reminiscent of the argon-benzene molecule where the argon atom is loosely bound by a polarization (van der Waals) mechanism and thus leads to a very extended object lying near the dissociation limit. Such states are also suggested to dominate the structure of mesons [a_0(980), f_0(975)] and baryons [Lambda(1405)] with proposed Kaon molecular structure (e.g. by Dalitz) near threshold. The inspection of such states throughout Physics allows us to gain insight into this phenomenon and suggest that a new collective Molecular Dipole Degree of Freedom plays a major role in the structure of hadrons (halo nuclei, mesons and baryons), and that quantitative tools such as the E1 Molecular Sum Rule are useful for elucidating the nature of the observed low lying E1 strength in halo nuclei.
Photon data shed new light upon the GDR spreading width in heavy nuclei
2008-10-14
A global study of the electric dipole strength in and below the isovector giant dipole resonance (GDR) is presented for mass numbers A>80. It relies on the recently established remarkably good match between data for the nuclear photo effect to novel photon scattering data covering the region below the neutron emission threshold as well as by average resonance neutron capture (ARC). From the wide energy coverage of these data the correlation of the GDR spreading width with energy can be studied with remarkable accuracy. A clear sensitivity to details of the nuclear shape, i.e. the beta- and gamma-deformations, is demonstrated. Based hereon a new parameterization of the energy dependence of the nuclear electric-dipole strength is proposed which - with only two new parameters - allows to describe the dipole strength in all heavy nuclei with A>80. Although it differs significantly from previous parameterizations it holds for spherical, transitional, triaxial and well deformed nuclei. The GDR spreading width depends in a regular way on the respective resonance energy, but it is independent of the photon energy.
Sub-wavelength interference in macroscopic observation
2004-11-29
We study the generalized Young's double-slit interference for the beam produced in the spontaneous parametric down-conversion (SPDC). It has been found that the sub-wavelength interference can occur macroscopically in both the two-photon intensity measurement and the single-photon spatial intensity-correlation measurement. The former refers to the quantum entanglement and the latter originates from the thermal spatial correlation. We show the visibility and the strength of the interference fringe related to the SPDC interaction, which may provide a strong sub-wavelength lithography with a moderate visibility in practical application.
Doppler-free two-photon-excited fluorescence spectroscopy of atomic hydrogen in flames
We describe Doppler-free 205-nm two-photon excitation studies of atomic hydrogen performed using a single-mode pulsed dye-laser system in low-pressure flames. Excitation spectra confirm calculated line-strength ratios for transitions to the 3{ital S} and 3{ital D} states. Collisional broadening rates are obtained in several flames and compared with quenching rates measured in the same flames, using time-resolved fluorescence measurements.
Doppler-free two-photon-excited fluorescence spectroscopy of atomic hydrogen in flames
1990-07-15
We describe Doppler-free 205-nm two-photon excitation studies of atomic hydrogen performed using a single-mode pulsed dye-laser system in low-pressure flames. Excitation spectra confirm calculated line-strength ratios for transitions to the 3{ital S} and 3{ital D} states. Collisional broadening rates are obtained in several flames and compared with quenching rates measured in the same flames, using time-resolved fluorescence measurements.
Doppler-free two-photon-excited fluorescence spectroscopy of atomic hydrogen in flames
1990-01-01
We describe Doppler-free 205-nm two-photon excitation studies of atomic hydrogen performed using a single-mode pulsed dye-laser system in low-pressure flames. Excitation spectra confirm calculated line-strength ratios for transitions to the 3S and 3D states. Collisional broadening rates are obtained in several flames and compared with quenching rates measured in the same flames, using time-resolved fluorescence measurements
2010-01-05
Optical fiber tapers are used to collect photoluminescence emission at ~1.5 um from photonic crystal cavities fabricated in erbium doped silicon nitride on silicon. Photoluminescence collection via fiber taper is enhanced 2.5 times relative to free space, with a total taper collection efficiency of 53%. By varying the fiber taper offset from the cavity, a broad tuning range of coupling strength is obtained. This material system combined with fiber taper collection is promising for building on-chip optical amplifiers.
Axions, their Relatives and Prospects for the Future
2008-11-26
The observation of a non-vanishing rotation of linear polarized laser light after passage through a strong magnetic field by the PVLAS collaboration has renewed the interest in light particles coupled to photons. Axions are a species of such particles that is theoretically well motivated. However, the relation between coupling and mass predicted by standard axion models conflicts with the PVLAS observation. Moreover, light particles with a coupling to photons of the strength required to explain PVLAS face trouble from astrophysical bounds. We discuss models that can avoid these bounds. Finally, we present some ideas to test these possible explanations of PVLAS experimentally.
1997-02-01
We derive an analytic form for the Heisenberg-Euler Lagrangian in the limit where the component of the electric field parallel to the magnetic field is small. We expand these analytic functions to all orders in the field strength (F{sub {mu}{nu}}F{sup {mu}{nu}}) in the limits of weak and strong fields, and use these functions to estimate the pair-production rate in arbitrarily strong electric fields and the photon-splitting rate in arbitrarily strong magnetic fields. {copyright} {ital 1997} {ital The American Physical Society}
1997-01-01
We derive an analytic form for the Heisenberg-Euler Lagrangian in the limit where the component of the electric field parallel to the magnetic field is small. We expand these analytic functions to all orders in the field strength (FmunuFmunu) in the limits of weak and strong fields, and use these functions to estimate the pair-production rate in arbitrarily strong electric fields and the photon-splitting rate in arbitrarily strong magnetic fields. copyright 1997 The American Physical Society
A "poor man's approach" to modelling of micro-structured optical fibres
Based on the scalar Helmholtz equation and the finite-difference approximation, we formulate a matrix eigenvalue problem for the calculation of propagation constants, beta(omega), in micro-structured optical fibres. The method is applied to index-guiding fibres as well as air-core photonic bandgap fibres, and in both cases qualitatively correct results are found. The strength of this approach lies in its very simple numerical implementation and its ability to find eigenmodes at a specific eigenvalue, which is of great interest, when modelling defect modes in photonic bandgap fibres.
SU(3) symmetries in exotic neutron-rich nuclei
We examine the structure of the exotic neutron-rich nucleus {sup 11}Li with an emphasis on understanding the origin of the soft E1 resonance and the neuron halo. The similarities and differences between shell model and di-neutron cluster model descriptions of the system are displayed using the Hecht expansion techniques. We find that the ground state {sup 11}Li as described in large shell model calculations is well approximated by the di-neutron cluster state. In contrast to the ground state, the soft E1 model of {sup 11}Li appears to have a more complicated structure and the E1 strength of this resonance is very sensitive to cancellations between p{yields}s and p{yields}d contributions to the dipole matrix elements. 12 refs., 6 figs., 3 tabs.
SU(3) symmetries in exotic neutron-rich nuclei
We examine the structure of the exotic neutron-rich nucleus {sup 11}Li with an emphasis on understanding the origin of the soft E1 resonance and the neuron halo. The similarities and differences between shell model and di-neutron cluster model descriptions of the system are displayed using the Hecht expansion techniques. We find that the ground state {sup 11}Li as described in large shell model calculations is well approximated by the di-neutron cluster state. In contrast to the ground state, the soft E1 model of {sup 11}Li appears to have a more complicated structure and the E1 strength of this resonance is very sensitive to cancellations between p{yields}s and p{yields}d contributions to the dipole matrix elements. 12 refs., 6 figs., 3 tabs.
Accelerated aging and stabilization of radiation-vulcanized EPDM rubber
2000-03-01
The effect of different antioxidants and their mixtures on the thermal aging and accelerated weathering of {gamma}-radiation vulcanized EPDM rubber in presence of crosslinking coagent, was investigated. The compounds used were either a synergistic blend of phenolic and phosphite antioxidants, i.e. 1:4 Irganox 1076: Irgafos 168 or a blend of arylamine and quinoline type antioxidants, i.e. 1:1 IPPD:TMQ, at fixed concentration. Tinuvin 622 LD hindered amine light stabilized (HALS) was also used. The response was evaluated by the tensile strength and elongation at break for irradiated samples after thermal aging at 100 deg. C for 28 days and accelerated weathering (Xenon test) up to 200 h. (author)
Accelerated aging and stabilization of radiation-vulcanized EPDM rubber
2000-01-01
The effect of different antioxidants and their mixtures on the thermal aging and accelerated weathering of gamma-radiation vulcanized EPDM rubber in presence of crosslinking coagent, was investigated. The compounds used were either a synergistic blend of phenolic and phosphite antioxidants, i.e. 1:4 Irganox 1076: Irgafos 168 or a blend of arylamine and quinoline type antioxidants, i.e. 1:1 IPPD:TMQ, at fixed concentration. Tinuvin 622 LD hindered amine light stabilized (HALS) was also used. The response was evaluated by the tensile strength and elongation at break for irradiated samples after thermal aging at 100 deg. C for 28 days and accelerated weathering (Xenon test) up to 200 h. (author)
The impact of models for E1 gamma-ray strength functions in the mass region A=140-200
1994-12-31
Hauser-Feshbach calculations of capture cross sections require among other ingredients gamma-ray strength functions f{sub XL} for various multipole orders XL. We assess the validity of various models for the dominating E1 strength by demanding the simultaneous reproduction of various experimental data related to neutron capture. For the strength of the other less important multipole radiations simple global prescriptions are used. None of the commonly used f{sub EI} models gives satisfactory results in the whole mass range A=140-200. In order to obtain an E1 strength function prescription for the whole mass region, we employ an enhancement in terms of two parameters of the width of the {open_quotes}generalised Lorentzian{close_quotes} model. In view of cross section calculations we study the systematics of these parameters.
Finite element model for the creep analysis of composite steel-concrete push tests
2007-01-01
Composite steel-concrete structures are employed extensively in modern high rise buildings and bridges. Even though the combination of steel and concrete enhances the strength and stiffness of the composite beams, the time-dependent behaviour of concrete may weaken the strength of the shear connection. When the concrete loses its strength, it will transfer its stresses to the structural steel through the shear studs. This behaviour will reduce the strength of the composite member. This paper presents the development of an accurate finite element model using ABAQUS to study the behaviour of shear connectors in push tests incorporating the time-dependent behaviour of concrete. The structure is modelled using three-dimensional solid elements for the structural steel beam, shear connectors, concrete slab and profiled sheeting. The finite element analyses indicated that the slip ductility, the strength and the stiffness of the composite member were reduced with respect to time. Further experiments to validate the models presented herein will be conducted and reported at a later stage.2007E1Yes Publisher: Singapore Research Publishing Format: 6 Other identifier: ; URN:ISBN:9789810593667 Language: eng Source: Proceedings of the Fifth International Conference on Advances in Steel Structures pp:400 - 395
Photon Strength Functions of Heavy Nuclei: Achievements and Open Problems
2009-01-01
Experimental studies of gamma decay of highly excited levels in nuclei started as early as 60 years ago. Soon, it turned out that this decay is strongly dominated by E1 transitions and that it is closely related to the giant electric dipole resonances built not only on the ground state, but also on each excited level, including the levels in the quasicontinuum. These findings brought the first evidence for the electric dipole vibrations coupled to the excited levels and demonstrated viability of Brink's concept. Nevertheless, with growing information on gamma rays following neutron capture it emerged that extrapolation of the photonuclear cross sections to the energy region below the neutron separation energy leads in some cases to overpredictions of the E1 photon strength. Several theories were developed, but this disproportion has not yet been ...
Equilibration and Out-of-equilibrium Effect in Relativistic Heavy Ion Collisions
The approach of a parton plasma at future heavy ion colliders towards kinetic and chemical equilibrium is considered. A plasma with a self-consistent evolving parton-parton interaction strength is shown to equilibrate better and faster than the usual but inconsistent one with a fixed strength. We explain why as a consequence of this, a parton plasma is a unique kind of many-body system. Because our time evolution scheme does not require the plasma to be in either kind of equilibrium from the outset, out-of-equilibrium effect on particle productions can be revealed. We show this on photon production and discuss the implications on photon as a signal to detect the quark-gluon plasma.
1990-03-01
This paper presents a new radiation diagnostic for assaying the energy spectrum and the angular distribution of energetic ions incident on thick hydrogen-rich thermal targets. This diagnostic compares the number of emergent photons in the narrow neutron capture line at 2.223 MeV to the number of Compton scattered photons that form a low-energy tail on the line. It is shown that the relative strength of the tail can be used as a measure of the hardness of the incident ion-energy spectrum. Application of this diagnostic to solar flare conditions is the main thrust of the work presented here. It is examined how the strength of the Compton tail varies with flare viewing angle and the angular distribution of the flare-accelerated particles. Application to compact X-ray binary systems is also briefly discussed. 39 refs.
2010-01-22
Two methods based on bremsstrahlung were applied to the stable even Mo isotopes for the experimental determination of the photon strength function covering the high excitation energy range above 4 MeV with its increasing level density. Photon scattering was used up to the neutron separation energies Sn and data up to the maximum of the isovector giant resonance(GDR) were obtained by photo-activation. After a proper correction for multi-step processes the observed quasi-continuous spectra of scattered photons show a remarkably good match to the photon strengths derived from nuclear photo effect data obtained previously by neutron detection and corrected in absolute scale using the new activation results. The combined data form an excellent basis to derive a shape dependence of the E1 strength in the even Mo isotopes with increasing deviation from the N = 50 neutron shell, i.e. with the impact of quadrupole deformation and triaxiality. The wide energy coverage of the data allows for a stringent assessment of the dipole sum-rule, and a test of a novel parameterization developed previously which is based upon. This parameterization for the electric dipole strength function in nuclei with A>80 deviates significantly from prescriptions generally used previously. In astrophysical network calculations it may help to quantify the role the p-process plays in the cosmic nucleosynthesis. It also has impact on the accurate analysis of neutr on capture data of importance for future nuclear energy systems and waste transmutation.
Two-photon absorption properties of meso-substituted A3-corroles
2008-01-01
We report for the first time two-photon absorption (2PA) cross sections and spectra of corroles within a broad spectral range of excitation wavelengths, 800-1400nm. Compared to symmetrically-substituted porphyrins, the 2PA spectrum of corroles contains a distinct peak at the laser wavelength close to twice the wavelength of Soret maximum (850nm), with a quite significant cross section, 2=60-130GM. Lowering of the symmetry relaxes the parity selection rules for 2PA, thus making the Soret band allowed for two-photon transition. We also observe that the strength of the 2PA peak in Soret region strongly decreases with the electron-withdrawing ability of the side substituents.
Thermo-mechanical optimization of photon shutter 1 for APS front ends
Photon shutter 1 (PS1) is one of the most critical elements on the front end of the beamlines at the Advanced Photon Source (APS) now under construction at Argonne National Laboratory (ANL). The PS1 uses an enhanced heat transfer tube developed at ANL. Due to large thermal loads on these components, inclined geometry is used in the design to spread the footprint of the x-ray beam. Even then, thermal loads are very critical. To address the thermal and thermo-mechanical issues, analytical studies have been applied to a simplified model of the shutter tube. The maximum temperature and maximum effective stress have been parametrically studied. Results for maximum temperatures and stresses are obtained and compared with the available strength/fatigue data for the materials proposed for the shutter design.
Thermo-mechanical optimization of photon shutter 1 for APS front ends
1992-07-28
Photon shutter 1 (PS1) is one of the most critical elements on the front end of the beamlines at the Advanced Photon Source (APS) now under construction at Argonne National Laboratory (ANL). The PS1 uses an enhanced heat transfer tube developed at ANL. Due to large thermal loads on these components, inclined geometry is used in the design to spread the footprint of the x-ray beam. Even then, thermal loads are very critical. To address the thermal and thermo-mechanical issues, analytical studies have been applied to a simplified model of the shutter tube. The maximum temperature and maximum effective stress have been parametrically studied. Results for maximum temperatures and stresses are obtained and compared with the available strength/fatigue data for the materials proposed for the shutter design.
The data recorded at a centre-of-mass energy of 189GeV by the OPAL detector at LEP are used to search for trilinear couplings of the neutral gauge bosons in the process e+e- --> Z-gamma. The cross-sections are measured for multihadronic events with an energetic isolated photon and for events with a high energy photon accompanied by missing energy. These cross-sections and the photon energy, polar angle and isolation angle distributions are compared to the Standard Model predictions and to the theoretical expectations of a model allowing for Z-gamma-Z and Z-gamma-gamma vertices. Since no significant deviations with respect to the Standard Model expectations are found, constraints are derived on the strength of neutral trilinear gauge couplings.
Quantum noise generated by four-wave mixing process within a fiber ring resonator
2010-01-01
We have analyzed the dissipative effect of the entangled photons generated by a nonlinear optical ring resonator from a non-degenerate four-wave mixing (FWM) process. The system and reservoir Hamiltonian are established in the interaction picture. To eliminate the reservoir operators, the Markov approximation is used and result them in a Linblad form in the master equation. Consequently, the positive P representation can recast this equation to the Fokker-Planck equation, and then the stochastic differential equations i.e., the entangled photon state equation of motion for photons propagating in the fiber, are obtained and easy to analyze numerically. Results obtained have shown that the entangled strength measurement depends on three main factors; first the nonlinear susceptibility of the...
Pseudoscalar Perturbations and Polarization of the Cosmic Microwave Background
2009-01-01
We show that models of new particle physics containing massless pseudoscalar fields superweakly coupled to photons can be very efficiently probed with CMB polarization anisotropies. The stochastic pseudoscalar fluctuations generated during inflation provide a mechanism for converting E-mode polarization to B-mode during photon propagation from the surface of last scattering. The efficiency of this conversion process is controlled by the dimensionless ratio H/(2pifa), where H is the Hubble scale during inflation, and fa-1 is the strength of the pseudoscalar coupling to photons. The current observational limits on the B mode constrain this ratio to be less than 0.07, which in many models of inflation translates to a sensitivity to fa exceeding 1014 GeV, which surpasses other tests
2007-02-15
Recently, the PVLAS collaboration has reported evidence for an anomalous rotation of the polarization of light in vacuum in the presence of a transverse magnetic field. This may be explained through the production of a new light spin-zero (axion-like) neutral particle coupled to two photons. In this letter-of-intent, we propose to test this hypothesis by setting up a photon regeneration experiment which exploits the photon beam of a high-power infrared laser, sent along the transverse magnetic field of a superconducting HERA dipole magnet. The proposed1 ALPS (Axion-Like Particle Search) experiment offers a window of opportunity for a rapid firm establishment or exclusion of the axion-like particle interpretation of the anomaly published by PVALS. It will also allow for the measurement of mass, parity, and coupling strength of this particle. (orig.)
2007-01-01
Recently, the PVLAS collaboration has reported evidence for an anomalous rotation of the polarization of light in vacuum in the presence of a transverse magnetic field. This may be explained through the production of a new light spin-zero (axion-like) neutral particle coupled to two photons. In this letter-of-intent, we propose to test this hypothesis by setting up a photon regeneration experiment which exploits the photon beam of a high-power infrared laser, sent along the transverse magnetic field of a superconducting HERA dipole magnet. The proposed1 ALPS (Axion-Like Particle Search) experiment offers a window of opportunity for a rapid firm establishment or exclusion of the axion-like particle interpretation of the anomaly published by PVALS. It will also allow for the measurement of mass, parity, and coupling strength of this particle. (orig.)
2008-01-01
Two independent groups have published intrinsic dosimetry parameters for the recently introduced OptiSeed103 interstitial brachytherapy source which contains 103Pd encapsulated by a novel polymer shell. The dose rate constant (LAMBDA) reported by the two groups, however, differed by more than 6% and there is currently no AAPM recommended consensus value for this source in clinical dosimetry. The aim of this work was to perform an independent determination of LAMBDA for the OptiSeed103 source using a recently developed photon spectrometry technique. Three OptiSeed103 sources (model 1032P) with known air-kerma strength were used in this study. The photon energy spectrum emitted along the radial direction on the source's bisector was measured in air using a high-resolution intrinsic ...
2009-06-09
Structured, periodic optical materials can be used to form photonic crystals capable of dispersing, routing, and trapping light. A similar phenomena in periodic elastic structures can be used to manipulate mechanical vibrations. Here we present the design and experimental realization of strongly coupled optical and mechanical modes in a planar, periodic nanostructure on a silicon chip. 200-Terahertz photons are co-localized with mechanical modes of Gigahertz frequency and 100-femtogram mass. The effective coupling length, which describes the strength of the photon-phonon interaction, is as small as 2.9 microns, which, together with minute oscillator mass, allows all-optical actuation and transduction of nanomechanical motion with near quantum-limited sensitivity. Optomechanical crystals have many potential applications, from RF-over-optical communication to the study of quantum effects in mesoscopic mechanical systems.
Optimization of coupling between photonic crystal resonator and curved microfiber
2005-08-12
The evanescent coupling from a photonic crystal resonator to a micron-thick optical fiber is investigated in detail by using a 3D-FDTD method. Properly designed photonic crystal cavity and taper structures are proposed, and optimal operating conditions are found to enhance the coupling strength while suppressing other cavity losses including the coupling to the slab propagating mode and to the higher-order fiber mode. In simulation, the coupling into the fundamental fiber mode is discriminated from other cavity losses by spatial and parity filtering of the FDTD results. The coupling efficiency of more than 80% into the fundamental fiber mode together with a total Q factor of 5,200 is achieved for the fiber diameter of 1.0 um and the air gap of 200 nm between the fiber and the cavity.
2007-01-01
The superconducting electron accelerator ELBE at Rossendorf delivers electron beams of energies up to 20 Me V with average currents up to 1 mA for experiments using photon-induced reactions. The Bremsstrahlung facility installed at this accelerator and the experimental area were designed such that the production of neutrons and the scattering of photons from surrounding materials are strongly reduced. We have investigated the nuclides 92Mo, 98Mo and 100Mo in photon-scattering experiments at electron energies from 6 to 13 Me V. Several hundred dipole transitions were observed in each of the nuclides. The experimental dipole-strength distributions of the nuclei are compared with calculations on the basis of a quasiparticle-random-phase approximation for deformed nuclei. Statistical approaches to the correction of level feeding ...
NLC Polarized Positron Photon Beam Target Thermal Structural Modeling
2002-06-11
The NLC polarized positron photon beam target is a 0.4 radiation length thick titanium target. Energy deposition from one pulse occurs over 266 nano-seconds and results in heating of the target and pressure pulses straining the material. The 22.1 MeV photon beam has a spot size of 0.75 mm and results in a maximum temperature jump of 233 C. Stresses are induced in the material from thermal expansion of the hotter material. Peak effective stresses reach 19 Ksi (1.34 x 10{sup 8} Pa), which is lower than the yield strength of a titanium alloy by a factor of six.
Klein-Nishina steps in the energy spectrum of galactic cosmic-ray electrons
2010-01-01
The full Klein-Nishina cross-section of the inverse Compton scattering interactions of electrons implies a significant reduction of the electron energy loss rate compared with the Thomson limit when the electron energy exceeds the critical Klein-Nishina energy EK=gammaKmec2=0.27m2ec 4/(kBT), where T denotes the temperature of the photon graybody distribution. As a consequence, the total radiative energy loss rate of single electrons exhibits sudden drops in the overall gamma-dot alpha gamma2-dependence when the electron energy reaches the critical Klein-Nishina energy. The strength of the drop is proportional to the energy density of the photon radiation field. The diffuse galactic optical photon ...
Elliptic flow of thermal photons at midrapidity in Au+Au collisions at sq root(SNN)=200GeV
2009-01-01
The elliptic flow v2 of thermal photons at midrapidity in Au+Au collisions at sq root(SNN)=200GeV is predicted, based on three-dimensional ideal hydrodynamics. Because of the interplay between the asymmetry and the strength of the transverse flow, the thermal photon v2 reaches a maximum at pTapprox2GeV/c and the pT-integrated v2 reaches a maximum at about 50% centrality. The pT-integrated v2 is very sensitive to the lower limit of the integral but not sensitive to the upper limit due to the rapid decrease in the spectrum of the transverse momentum
A microwave beam waveguide undulator for a brilliant above 100 keV photon source.
For generation of photons above 100-keV with a magnetic field strength in the range 0.2-0.5 Tesla, an undulator wavelength {lambda}{sub u} shorter than 5 mm may be needed with beam in the Advanced Photon Source (APS) storage ring. A microwave beam waveguide undulator system has been investigated for generation of such light. The waveguide structure consists of two parallel reflector surfaces that can be derived from an elliptically cylindrical waveguide. The structure can support deflecting TE{sub m0} modes with very low microwave loss. A microwave ring resonator circuit employing the beam waveguide is considered to construct an undulator with the above requirement. Microwave properties of the beam waveguide structure have been investigated, and the design criteria for a microwave undulator are discussed.
A microwave beam waveguide undulator for a brilliant above 100 keV photon source.
1999-04-19
For generation of photons above 100-keV with a magnetic field strength in the range 0.2-0.5 Tesla, an undulator wavelength {lambda}{sub u} shorter than 5 mm may be needed with beam in the Advanced Photon Source (APS) storage ring. A microwave beam waveguide undulator system has been investigated for generation of such light. The waveguide structure consists of two parallel reflector surfaces that can be derived from an elliptically cylindrical waveguide. The structure can support deflecting TE{sub m0} modes with very low microwave loss. A microwave ring resonator circuit employing the beam waveguide is considered to construct an undulator with the above requirement. Microwave properties of the beam waveguide structure have been investigated, and the design criteria for a microwave undulator are discussed.
Photon condensation and its phase diffusion
2009-12-11
Recently, several experiments successfully achieved the strong coupling of a BEC of $ N \\sim 10^{5} $ $ ^{87}Rb $ atoms to the photons inside an ultrahigh-finesse optical cavity. The strong coupling regime was also achieved with artificial atoms such as superconducting qubits inside micro-wave circuit cavity. These systems are described by the Dicke model where a single mode of photons coupled to an assembly of $ N $ atoms with the same coupling strength $ g $. In this paper, by solving the Dicke model by $ 1/ N $ expansion, we show that at the thermodynamic limit $ N = \\infty $, one can achieve the Bose-Einstein Condensation (BEC) of the cavity photons at sufficiently strong coupling $ g $. At a finite $ N $, we identify an emergent quantum phase diffusion mode inside the BEC phase and also work out many remarkable experimental consequences of this mode such as its low frequency, photon number squeezing properties and photon statistics. The photons from the BEC phase are in a number squeezed state with much enhanced signal/noise ratio which may have wide applications in the field of high resolution, high sensitive measurement and also in quantum information processing. The effects of dissipations due to leaking photons out of the cavity are also briefly discussed. The difference with a Laser beam is stressed. Several experimental schemes to realize the BEC of the photons and detect the phase diffusion mode are proposed.
2009-12-21
Features of screening and confinement are studied for the coupling of axial torsion fields with photons in the presence of an external electromagnetic field. To this end we compute the static quantum potential. Our discussion is carried out using the gauge-invariant but path-dependent variables formalism which is alternative to the Wilson loop approach. Our results show that, in the case of a constant electric field strength expectation value, the static potential remains Coulombic, while in the case of a constant magnetic field strength expectation value the potential energy is the sum of a Yukawa and a linear potential, leading to the confinement of static probe charges.
Complementarity in variable strength quantum non-demolition measurements
2009-01-01
Using a linear optic quantum gate we perform a variable strength quantum non-demolition measurement, to elucidate the role of which-path knowledge in a complementarity experiment. Specifically, we demonstrate that the entanglement created by the measurement interaction prevents an exhaustive description in terms of complementary wave-like and particle-like behaviour of a single photon in an interferometer. Publisher: Institute of Physics Publishing Contributor: Eberhard Bodenschatz Coverage: 2009-09-14T00:00:00Z
Automatic beamline calibration procedures
1992-01-01
Recent experience with the SLC and SPEAR accelerators have led to a well-defined set of procedures for calibration of the beamline model using the orbit fitting program, RESOLVE. Difference orbit analysis is used to calibrate quadrupole strengths, BPM sensitivities, corrector strengths, focusing effects from insertion devices, and to determine the source of dispersion and coupling errors. Absolute orbit analysis is used to locate quadrupole misalignments, BPM offsets, or beam loss. For light source applications, the photon beam source coordinates can be found. Automatic beamline calibration procedures are outlined and illustrated with recent examples. (author) 5 refs. 4 figs
Optical properties of semiconductors quantum microcavity structures
1996-12-01
The principal phenomenon investigated in this thesis is vacuum Rabi coupling in semiconductor microcavity structures. In these structures quantum well excitons are embedded in a Fabry - Perot like cavity, defined by two semiconductor dielectric mirrors. In such a system the coupled exciton and cavity photon mode form a mixed - mode polariton, where on - resonance there are two branches, each having 50% exciton and 50% photon character. The separation between the upper and lower branches is a measure of the coupling strength where the strength is dependent on the exciton oscillator strength. This interaction is known as vacuum Rabi coupling, and clear anticrossing is seen when the exciton is tuned through the cavity. In our reflectivity experiments we demonstrate control of the coupling between the cavity mode and the exciton by varying temperature, applied electric or magnetic field. Modelling of the reflectivity spectra and the tuning was done using a Transfer Matrix Reflectivity (TMR) model or a linear dispersionmodel, where in both cases the excitons are treated as Lorentz oscillators. Temperature tuning is achieved because exciton energy decreases with temperature at a much faster rate than the cavity mode. We have demonstrated vacuum Rabi coupling of the cavity mode with both the heavy - hole and light - hole excitons. Electric field tuning is achieved via the quantum confined Stark effect which decreases the exciton energy with increasing field, whilst at the same time the cavity mode energy remains constant. A study of how the electric field reduction of exciton oscillator strength reduces the vacuum Rabi coupling strength is performed. We report the first observation in a semiconductor structure of motional narrowing, seen in both electric field and in temperature tuning experiments at high magnetic field. In magnetic field studies we show how magnetic field induced increase in exciton oscillator strength affects the vacuum Rabi coupling. We also show by circular polarisation measurements on-resonance that each Zeeman split component of the exciton interacts only with the appropriately circularly polarised component of the photon mode. (author)
2009-01-01
Polymer gels are generally assumed to exhibit no significant dependence of the dose response on the energy or type of irradiation for clinically used beam qualities. Based on reports on differences in dose response for low energy photons and particle beams with high linear energy transfer (LET) we here investigate the dose response and energy dependence for a normoxic methacrylic acid polymer gel (MAGAT) for X-rays (100 kV), high energy photon beams (E = 1.2 MeV (60Co), 6 MV and 15 MV) and for three different electron energies (4, 12 and 20 MeV). Due to the possible impact also the sensitivity of the dose response to the dose rate is reported. A reduction in polymer gel relaxation rate has been observed for proton and carbon beams due to the high Linear Energy Transfer (LET) of these types of radiations. We here report on the dose response of an acryl-amide polymer gel (PAG) in a ...
Oscillator strength, transition rates and lifetimes for n=3 states in Al-like ions
Transition rates, oscillator strengths, and line strengths are calculated for the 3220 possible electric-dipole (E1) transitions between the 73 even-parity 3s3p sup 2 , 3s sup 2 3d, 3p sup 2 3d, 3d sup 2 3s and 3d sup 3 states and the 75 odd-parity 3s sup 2 3p, 3p sup 3 , 3s3p3d, and 3d sup 2 3p states in Al-like ions with the nuclear charges ranging from Z=15 to 100. Relativistic many-body perturbation theory (MBPT), including the Breit interaction, is used to evaluate retarded E1 matrix elements in length and velocity forms. The calculations start from a 1s sup 2 2s sup 2 2p sup 6 Dirac-Fock potential. First-order MBPT is used to obtain intermediate coupling coefficients and second-order MBPT is used to calculate transition matrix elements. Contributions from negative-energy states are included in the second order E1 matrix elements to ensure gauge-independence of transition amplitudes. The transition energies used in the calculation of oscillator strengths and transition rates are from second-order MBPT. Transition rates, line strengths, and oscillator strengths are compared with critically evaluated experimental values and with results from other recent calculations. As a result, we present data for the selected transition, that includes transitions between the 10 even-parity 3s3p sup 2 , 3s sup 2 3p states and the 29 odd-parity 3s sup 2 3p, 3p sup 3 , and 3s3p3d states in Al-like ions. Trends of the transition rates as functions of Z are illustrates graphically for the 220 transitions. Lifetimes of the 10 possible even-parity lower levels and the 27 possible odd-parity upper levels are given for Z=15-100.
Chameleon-Photon Mixing in a Primordial Magnetic Field
2010-03-02
We consider the non-resonant mixing between photons and scalar axion-like particles (ALPs) in a primordial magnetic field, with specific reference to the chameleon scalar field model. This mixing would affect the intensity and polarization state of the cosmic microwave background (CMB) radiation. We find that the average modification to the CMB polarization modes is negligible. However the average modification to the CMB intensity spectrum is more significant and we compare this to high precision measurements of the CMB monopole made by the far infrared absolute spectrophotometer (FIRAS) on board the COBE satellite. The resulting 95% confidence limit on the scalar-photon conversion probability in the primordial field (at 100 GHz) is P < 2.6x10^{-2}. This corresponds to a degenerate constraint on the photon-scalar coupling strength, g, and the magnitude of the primordial magnetic field. Taking the 95% confidence upper bound on the strength of the primordial magnetic field found by Kahniashvili et al., this would imply an upper bound on the photon-scalar coupling strength in the range g < 2.13x10^{-13}GeV^{-1} to g < 2.04x10^{-14} GeV^{-1}, depending on the power spectrum of the primordial magnetic field.
Linear response calculation using the canonical-basis TDHFB with a schematic pairing functional
2010-09-20
A canonical-basis formulation of the time-dependent Hartree-Fock-Bogoliubov (TDHFB) theory is obtained with an approximation that the pair potential is assumed to be diagonal in the time-dependent canonical basis. The canonical-basis formulation significantly reduces the computational cost. We apply the method to linear-response calculations for even-even nuclei. E1 strength distributions for proton-rich Mg isotopes are systematically calculated. The calculation suggests strong Landau damping of giant dipole resonance for drip-line nuclei.
Isomer spectroscopy in {sup 92}Ru and {sup 95}Pd
1996-12-31
The parity changing {gamma}-transitions like E1, M2, E3 in {sup 92}Ru and {sup 95}Pd nuclei have been investigated to probe the purity of the Shell Model. Two isomers of {sup 92}Ru and {sup 95}Pd have been produced in the {sup 58}Ni + {sup 40}Ca heavy ion reaction at {sup 58}Ni beams energy 215 MeV. The gamma-ray transition strength have been deduced. 10 refs, 2 figs, 1 tab.
Photon Splitting and Pair Conversion in Strong Magnetic Fields
2008-04-08
The magnetospheres of neutron stars provide a valuable testing ground for as-yet unverified theoretical predictions of quantum electrodynamics (QED) in strong electromagnetic fields. Exhibiting magnetic field strengths well in excess of a TeraGauss, such compact astrophysical environments permit the action of exotic mechanisms that are forbidden by symmetries in field-free regions. Foremost among these processes are single-photon pair creation, where a photon converts to an electron-positron pair, and magnetic photon splitting, where a single photon divides into two of lesser energy via the coupling to the external field. The pair conversion process is exponentially small in weak fields, and provides the leading order contribution to vacuum polarization. In contrast, photon splitting possesses no energy threshold and can operate in kinematic regimes where the lower order pair conversion is energetically forbidden. This paper outlines some of the key physical aspects of these processes, and highlights their manifestation in neutron star magnetospheres. Anticipated observational signatures include profound absorption turnovers in pulsar spectra at gamma-ray wavelengths. The shapes of these turnovers provide diagnostics on the possible action of pair creation and the geometrical locale of the photon emission region. There is real potential for the first confirmation of strong field QED with the new GLAST mission, to be launched by NASA in 2008. Suppression of pair creation by photon splitting and its implications for pulsars is also discussed.
Multi-photon fluorescence imaging through biological tissue and image reconstruction
2001-01-01
In this paper, image formation under single-photon (1-p), two-photon (2-p) and three-photon (3-p) fluorescence imaging through turbid media which consist of different sized scatterers has been investigated in detail. It has been demonstrated that the size of scattering particles plays an important role in determining whether to use 1-p, 2-p, or 3-p excitation. For small scatterers, where Rayleigh scattering is dominant, multi-photon excitation provides significantly better resolution. Such improvement reduces dramatically for large scatterers, where Mie scattering becomes dominant. Another disadvantage of using multi-photon fluorescence excitation in highly scattered media is that penetration depth is limited by fast dropping of signal strength in deep tissue imaging. In this paper, we introduce a deconvolution method with a novel concept of the effective point spread function, which is effective in restoring the loss of imaging resolution caused by multiple scattering in a tissue medium. Publisher: SPIE Contributor: Swinburne University of Technology. School of Biophysical Sciences and Electrical Engineering. Centre for Micro-Photonics Other identifier: swin:15353 Language: English Source: Proceedings of SPIE: Photon Migration, Optical Coherence Tomography, and Microscopy, Munich, Germany, 17 June 2001 / Stefan Andersson-Engels and Michael Kaschke (eds.), Vol. 4431, pp. 226-232 Rights: Copyright 2003 SPIE Society of Photo-Optical Instrumentation Engineers. This paper was originally published in Proceedings of SPIE (Vol. 4431), and is available from: http://dx.doi.org/10.1117/12.447426. The published version of the paper is reproduced here in accordance with the copyright policy of the publisher. One print or electronic copy may be made for personal use only. Systematic electronic or print reproduction and distribution, duplication of any material in this paper for a fee or for commercial purposes, or modification of the content of the paper are prohibited.
GeV and higher energy photon interactions in gamma-ray burst fireballs and surroundings
2004-01-01
We have calculated the opacities and secondary production mechanisms of high energy photons arising in gamma-ray burst internal shocks, using exact cross-sections for the relevant processes. We find that for reasonable choices of parameters, photons in the range of 10's to 100's of GeV may be emitted in the prompt phase. Photons above this range are subject to electron-positron pair production with fireball photons and would be absent from the spectrum escaping the gamma-ray burst. We find that, in such cases, the fireball becomes optically thin again at ultra-high energies ($\\gtrsim$ PeV). On the other hand, for sufficiently large fireball bulk Lorentz factors, the fireball is optically thin at all energies. Both for $\\gamma\\gamma$ self-absorbed and optically thin cases, the escaping high energy photons can interact with infra-red and microwave background photons to produce delayed secondary photons in the GeV-TeV range. These may be observable with GLAST, or at low redshifts with ground-based air Cherenkov telescopes. Detection of the primary prompt spectrum constrains the bulk Lorentz factor, while detection of delayed secondary gamma-rays would provide a consistency check for the primary spectrum and the bulk Lorentz factor as well as constraints on the intergalactic magnetic field strength.
1984-10-15
An inverse-photoemission study (at h..omega.. = 9.7 eV) of the adsorption of carbon monoxide on a Pd(111) surface is compared with a first-principles calculation of the cross section for the emission of photons as a function of electron angle of incidence. It is found that the calculation is able to explain the experimental results in terms of the relative strengths of the sigma..--> pi.. and ..pi --> pi.. channels in the optical transitions.
1984-10-15
An inverse-photoemission study (at h omega = 9.7 eV) of the adsorption of carbon monoxide on a Pd(111) surface is compared with a first-principles calculation of the cross section for the emission of photons as a function of electron angle of incidence. It is found that the calculation is able to explain the experimental results in terms of the relative strengths of the sigma ..-->.. ..pi.. and ..pi.. ..-->.. ..pi.. channels in the optical transitions.
1990-09-01
Simple methods were applied to investigate the characteristics of a Geiger-Mueller counter with Q-gas flowing at 1 atm. The propagation velocity of the photon-aided avalanche along the anode wire depends linearly on the strength of the electric field in the counter. Its fluctuation (FWHM) as a function of distance between the source position and the end point is discussed. (orig.).
1985-01-01
Sources of neutron and photon transport data are described as well as the processing of the evaluated data sets into continuous-energy and multigroup cross-section sets. The procedures for checking and validating the processed data are discussed. The question of why so many data sets are available is addressed by indicating the differences between data sets as well as their relative strengths and weaknesses. Suggestions are made to help the MCNP user in selecting appropriate cross-section sets. 31 refs.
Neutron resonance averaging with filtered beams
1985-01-01
Neutron resonance averaging using filtered beams from a reactor source has proven to be an effective nuclear structure tool within certain limitations. These limitations are imposed by the nature of the averaging process, which produces fluctuations in radiative intensities. The fluctuations have been studied quantitatively. Resonance averaging also gives us information about initial or capture state parameters, in particular the photon strength function. Suitable modifications of the filtered beams are suggested for the enhancement of non-resonant processes.
Self-consistent Skyrme QRPA for use in axially-symmetric nuclei of arbitrary mass
2010-06-02
We describe a new implementation of the quasiparticle random phase approximation (QRPA) in axially-symmetric deformed nuclei with Skyrme and volume-pairing energy-density functionals. After using a variety of tests to demonstrate the accuracy of the code in ^{24,26}Mg and ^{16}O, we report the first fully self-consistent application of the Skyrme QRPA to a heavy deformed nucleus, calculating strength distributions for several K^pi in ^{172}Yb. We present energy-weighted sums, properties of gamma-vibrational and low-energy K^pi=0^+ states, and the complete isovector E1 strength function. The QRPA calculation reproduces the properties of the low-lying 2^+ states as well or better than it typically does in spherical nuclei.
Modification of bone graft by blending with lecithin to improve hydrophilicity and biocompatibility
2008-01-01
Lecithin was blended to improve the hydrophilicity and biocompatibility of bone graft containing poly(l-lactic acid) (PLLA). Solution blending and freeze drying were used to fabricate symmetrical scaffolds containing different percentages of lecithin (lecithin: PLLA = 0, 5, 10 wt%). Scanning electron microscopy showed that the scaffolds maintained the three-dimensional porous structure. A water uptake experiment proved the significant improvement of hydrophilicity of the blend scaffold. With the addition of lecithin, the compressive strength and compressive modulus decreased. When the weight ratio of lecithin to PLLA was up to 10%, the compressive strength was still more than the lower limit of natural cancellous bone. To test the biocompatibility of the scaffolds, cell culture in vitro and subcutaneous implantation in vivo were performed. MC3T3-E1 ...
Continuum Random Phase Approximation for Relativistic Point Coupling Models
2009-07-21
Relativistic Continuum Random Phase Approximation (CRPA) is used to investigate collective excitation phenomena in several spherical nuclei along the periodic table. We start from relativistic mean field calculations based on a covariant density functional with density dependent zero range forces. From the same functional an effective interaction is obtained as the second derivative with respect to the density. This interaction is used in relativistic continuum-RPA calculations for the investigation of isoscalar monopole, isovector dipole and isoscalar quadrupole resonances of spherical nuclei. In particular we study the low-lying E1 strength in the vicinity of the neutron evaporation threshold. The properties of the resonances, such as centroid energies and strengths distributions are compared with results of discrete RPA calculations for the same model as well as with experimental data.
Analog E1 transitions and isospin mixing
We investigate whether isospin mixing can be determined in a model-independent way from the relative strength of E1 transitions in mirror nuclei. The specific examples considered are the A=31 and A=35 mirror pairs, where a serious discrepancy between the strengths of 7/2{sup -}{yields}5/2{sup +} transitions in the respective mirror nuclei has been observed. A theoretical analysis of the problem suggests that it ought to be possible to disentangle the isospin mixing in the initial and final states given sufficient information on experimental matrix elements. With this in mind, we obtain a lifetime for the relevant 7/2{sup -} state in {sup 31}S using the Doppler-shift attenuation method. We then collate the available information on matrix elements to examine the level of isospin mixing for both A=31 and A=35 mirror pairs.
1994-12-31
The photon scattering experiments were performed for the lower energy range up to 4 MeV at the Stuttgart Dynamitron and for the upper energy range up to 12 MeV at the Gent Linear Accelerator. By the measurement on the Er isotopes the systematic studies of the M1 scissor mode were supplemented in the region of the well deformed rare earth nuclei. The fragmentation of the transition strength increases to the lighter Er isotopes. In the measurement on {sup 164}Er only states with smaller transition strength than in the other isotopes were observed. Furthermore the summed strength is distinctly smaller than in {sup 166}Er.
1994-01-01
The photon scattering experiments were performed for the lower energy range up to 4 MeV at the Stuttgart Dynamitron and for the upper energy range up to 12 MeV at the Gent Linear Accelerator. By the measurement on the Er isotopes the systematic studies of the M1 scissor mode were supplemented in the region of the well deformed rare earth nuclei. The fragmentation of the transition strength increases to the lighter Er isotopes. In the measurement on 164Er only states with smaller transition strength than in the other isotopes were observed. Furthermore the summed strength is distinctly smaller than in 166Er
Continuous measurement feedback control of a Bose-Einstein condensate using phase-contrast imaging
2009-01-01
We consider the theory of feedback control of a Bose-Einstein condensate (BEC) confined in a harmonic trap under a continuous measurement constructed via nondestructive imaging. A filtering theory approach is used to derive a stochastic master equation (SME) for the system from a general Hamiltonian based upon system-bath coupling. Numerical solutions for this SME in the limit of a single atom show that the final steady-state energy is dependent upon the measurement strength, the ratio of photon kinetic energy to atomic kinetic energy, and the feedback strength. Simulations indicate that for a weak measurement strength, feedback can be used to overcome heating introduced by the scattering of light, thereby allowing the atom to be driven toward the ground state
2009-01-01
Photoneutron cross sections were measured for 117Sn and 116Sn near the neutron thresholds at 6.94 and 9.56 MeV, respectively, with quasi-monochromatic laser-Compton scattering gamma rays. The 117Sn cross section, which is strongly enhanced near the low threshold, provides evidence for the presence of extra gamma strength in the low-energy tail of the giant dipole resonance. A coherent analysis of the photoneutron data for 117Sn together with the neutron capture on 116Sn shows that the gamma-ray strength function is balanced in the photoneutron and neutron capture channels in terms of the microscopic Hartree-Fock-Bogoliubov plus quasiparticle random-phase approximation model of E1 strength combined with a pygmy E1 resonance at 8.5 MeV. The high-energy part of the ...
Strength of short high strength steel composite columns under biaxial bending
2004-01-01
High strength quenched and tempered structural steel has seen an increased usage in multistorey building construction. Many current international codes do not cater for the use of high strength steel and thus much needed research is required to give structural engineers the confidence to use this new and innovative material in a safe and efficient manner. This paper presents the results of an experimental program designed to consider the behaviour of short composite columns under biaxial bending. Coupled with these experiments is the assessment of current international design models for biaxial bending. The paper concludes with suggestions for further research.2004E1Yes Publisher: Korea Korea Science and Engineering Foundation Format: 10 Other identifier: ; URN:ISBN:8989693128 Language: eng Source: ICSCS04: Proceedings of the 2nd International Conference on Steel and Composite Structures, held in Seoul, Korea, 2-4 September, 2004 pp:1154 - 1145
First results from electron-photon damage equivalence studies on a generic ethylene-propylene rubber
1986-04-01
As part of a simulator adequacy assessment program, the relative effectiveness of electrons and photons to produce damage in a generic ethylene propylene rubber (EPR) has been investigated. The investigation was limited in extent in that a single EPR material, in three thickness, was exposed to Cobalt-60 photons and three electron beam energies. Basing material damage on changes in the EPR mechanical properties elongation and tensile strength, we observed that EPR damage was a smoothly varying function of absorbed energy and independent of irradiating particle type. EPR damage tracked equally well as a function of both incident particle energy and material front surface dose. Based on these preliminary data, we tentatively concluded that a correlation between particle, particle energy, and material damage (as measured by changes in material elongation and/or tensile strength) has been demonstrated. 14 figs.
2009-06-17
The re-analysis of the published experimental data on the primary gamma-transition intensities following neutron capture in different groups of neutron resonances in $^{156,158}$Gd has been performed. There are determined the most probable values of sum of E1 and M1 primary transitions, numbers of excited by them levels of both parities, ratios of radiative strength functions k(M1)/k(E1), dispersions of deviations of random values of intensities from the average and ratios of mean intensities of primary transitions to levels J=5/2 with respect to analogous data for J=1/2 and 3/2 (capture of the 24 keV neutrons) in narrow excitation energy intervals. All the data on level density and sums of radiative strength functions confirm the presence of clearly expressed step-like structure in level density below 3 MeV and general trend in change in strength functions as changing primary gamma-transition energy. Variations of distribution dispersions and, especially, ratio k(M1)/k(E1) (or $k(E1)/k(M1)$) at changing excitation energy point to strong change in structure of these nuclei above 1.0-1.5 MeV.
An investigation of giant Kerr nonlinearity
2002-01-01
This thesis investigates the properties of an atomic system exhibiting a giant Kerr nonlinearity. The atomic energy level scheme involves four energy levels. A three level A subsystem in the atom exhibits the effect of electromagnetically induced transparency (EIT), reducing the spontaneous emission noise. The fourth level leads to an ac-Stark shift of the ground state, which in turn leads to a giant, noiseless Kerr nonlinearity. Two different environments are explored. First, a system comprising of large number of atoms in an optical cavity is analysed. Detailed aspects of noise reduction in this system are investigated. In particular, strong squeezing in the quadrature in phase with the field driving the cavity mode is found, if the effective coupling of light to the atoms is strong. However, the linewidth of the predicted squeezing is found to be very narrow. This is attributed to a very steep linear susceptibility of the atomic medium. Since the widening of the squeezing window is possible only for weaker effective coupling, in turn reducing the squeezing level, a different environment is proposed. This involves a single four level atom, strongly coupled to the cavity mode. In such a strongly coupled system, the most appropriate approach is found to be that formulated in terms of polaritons – composite excitations of the 'atom-cavity molecule'. Adopting the polariton approach, nonclassical correlations in the field leaving the cavity are investigated. Strong photon antibunching is found and the effect of photon blockade predicted and described. The photon blockade effect can also be found in a system comprised of a two level atom coupled to the cavity mode, if the external driving is tuned to one of the vacuum Rabi resonances. A comparison between the two schemes is performed, and it is found that the four level scheme exhibits much better photon blockade. The reason for this is quantum interference between secondary transitions in the dressed states picture. Destructive interference cancels the transitions that would otherwise introduce a second photon into the system, hence producing a more robust photon blockade. All of these results are valid in the regime where external driving is weak. If the external driving strength is increased, the photon statistics (as measured by the zero-delay second order correlation function) changes from strong antibunching to strong bunching, over a relatively narrow range of driving strengths. The occurrence of this change can again be attributed to quantum interference. It is shown that the interference effect prevents the excitation of the composite system by a second photon, but not excitation by a two-photon transition (following the first excitation). Therefore, the third excitation manifold is excited, which then decays back to the first manifold in a two photon cascade. This two photon cascade is the source of correlated photon pairs causing an increase in the second order correlation function. The dynamics of forward scattering of light is presented, and nonclassical behaviour of the delay dependence of correlation function ('overshoots' and 'undershoots') is discussed. For the analytical treatment of this system, a method based on the polariton approach is devised, which includes the treatment of driving and damping. It is shown that this method is ideally suited to the analysis of strongly coupled systems, where only a few photons contribute to the dynamics. Publisher: ResearchSpace@Auckland Language: en Rights: Items in ResearchSpace are protected by copyright, with all rights reserved, unless otherwise indicated.; http://researchspace.auckland.ac.nz/docs/uoa-docs/rights.htm; Copyright: The author
Special concrete 1; Tokushu konkurito 1
1998-09-10
In this session, the lecture announcement was carried out on light cellular concrete, replanting concrete, photonic band gap, antimicrobe concrete as special concrete. Since the uniform bubble of that foaming agent was used further than foaming agent on the effect of the bubble distribution on dynamic characteristics of high-intense cement paste hardening body is easy to be obtained, in the light cellular concrete, it was reported that compression strength rises in the comparison of identical air quantity. The case there was a question for brittle with the strengthening, and there was a response of considering the fiber reinforcement. In the replanting concrete, the effect on aggregate grain diameter in the porous concrete of the vegetation basis, strength of the aggregate cement ratio, permeability, grass length quantity was reported, and it was shown that the growth of the grass became bad, when the aggregate cement ratio decreases, by the decrease in the connected void quantity. In photonic band gap, the relation of mixed state and rigidity and strength of the accelerating agent in the concrete was reported on ettringite system admixture and rigidity and strength of high-intense photonic band gap by combined use of accelerating agent and timbering performance in each. It was shown that the mixed state of accelerating agent became unequal that water cement ratio decreases with the cause to the fluctuation of the transfer-ness of the concrete of water cement ratio by the difference and that there is no strengthening by the decrease in the water cement ratio. There was a question of whether it could cope in the construction for it. In the latter, the expression of elastic modulus and compression strength remarkably increased by the use of the ettringite system admixture, and the possibility that it blew concerning the timbering performance and can reduce the pressure was shown. There was a question for the rebound by the high flow, and there was a response of the effect which could cope by type and mixture of the accelerating agent. In the antimicrobe concrete, though there was the condensation delayed, when physical property and antimicrobe effect of the mortar which mixed organic system antimicrobe medicine are reported, and when the additive rate of antimicrobe medicine increases, that there is no problem and that it obtains large antimicrobe effect were shown. There was a question on possibility such as not only contamination to persistence and mortar but also impregnation of antimicrobe medicine surface application impregnation of the antimicrobe effect for it. (translated by NEDO)
Searching for the light dark gauge boson in GeV-scale experiments
2009-04-14
We study current constraints and search prospects for a GeV scale vector boson at a range of low energy experiments. It couples to the Standard Model charged particles with a strength <= 10^-3 to 10^-4 of that of the photon. The possibility of such a particle mediating dark matter self-interactions has received much attention recently. We consider searches at low energy high luminosity colliders, meson decays, and fixed target experiments. Based on available data, searches both at colliders and in meson decays can discover or exclude such a scenario if the coupling strength is on the larger side. We emphasize that a dedicated fixed target experiment has a much better potential in searching for such a gauge boson, and outline the desired properties of such an experiment. Two different optimal designs should be implemented to cover the range of coupling strength 10^-3 to 10^-5, and < 10^-5 of the photon, respectively. We also briefly comment on other possible ways of searching for such a gauge boson.
Vacuum chamber thermal protection for the APS (Advanced Photon Source)
The addition of undulators and wigglers into synchrotron storage rings created new problems in terms of protecting the integrity of the ring vacuum chamber. If the photon beam from these devices were missteered into striking an inadequately cooled section of the storage ring vacuum chamber, the structural strength might be reduced sufficiently that the vacuum envelope could be penetrated, resulting in long downtime of the storage ring. The new generation of high-energy synchrotron light sources will produce photon beams of such high power density that cooling of the vacuum chamber will not prevent a potential penetration of the vacuum envelope, and other methods of preventing this occurrence will be required. Since active methods will be used to ensure that the beams are delivered to beam lines for users during normal operation, there is a need for passive protection methods during non-routine operation, such as turning on new beam lines, injection, etc., when the active systems may be disabled. In addition, the passive methods could prevent the problem from arising and provide the rapid time response necessary for the highest power beams, a property that might not be easily and reliably provided by active methods during the early operation of these machines. This paper summarizes the results of a task group that studied the problem and outlines passive methods of protection for the Advanced Photon Source (APS). 2 refs., 3 figs., 1 tab.
Vacuum chamber thermal protection for the APS (Advanced Photon Source)
1989-01-01
The addition of undulators and wigglers into synchrotron storage rings created new problems in terms of protecting the integrity of the ring vacuum chamber. If the photon beam from these devices were missteered into striking an inadequately cooled section of the storage ring vacuum chamber, the structural strength might be reduced sufficiently that the vacuum envelope could be penetrated, resulting in long downtime of the storage ring. The new generation of high-energy synchrotron light sources will produce photon beams of such high power density that cooling of the vacuum chamber will not prevent a potential penetration of the vacuum envelope, and other methods of preventing this occurrence will be required. Since active methods will be used to ensure that the beams are delivered to beam lines for users during normal operation, there is a need for passive protection methods during non-routine operation, such as turning on new beam lines, injection, etc., when the active systems may be disabled. In addition, the passive methods could prevent the problem from arising and provide the rapid time response necessary for the highest power beams, a property that might not be easily and reliably provided by active methods during the early operation of these machines. This paper summarizes the results of a task group that studied the problem and outlines passive methods of protection for the Advanced Photon Source (APS). 2 refs., 3 figs., 1 tab.
Microscopic Approach to Analyze Solar-Sail Space-Environment Effects
2009-01-05
Near-sun space-environment effects on metallic thin films solar sails as well as hollow-body sails with inflation fill gas are considered. Analysis of interaction of the solar radiation with the solar sail materials is presented. This analysis evaluates worst-case solar radiation effects during solar-radiation-pressure acceleration. The dependence of the thickness of solar sail on temperature and on wavelength of the electromagnetic spectrum of solar radiation is investigated. Physical processes of the interaction of photons, electrons, protons and helium nuclei with sail material atoms and nuclei, and inflation fill gas molecules are analyzed. Calculations utilized conservative assumptions with the highest values for the available cross sections for interactions of solar photons, electrons and protons with atoms, nuclei and hydrogen molecules. It is shown that for high-energy photons, electrons and protons the beryllium sail is mostly transparent. Sail material will be partially ionized by solar UV and low-energy solar electrons. For a hollow-body photon sail effects including hydrogen diffusion through the solar sail walls, and electrostatic pressure is considered. Electrostatic pressure caused by the electrically charged sail's electric field may require mitigation since sail material tensile strength decreases with elevated temperature.
Entangled photons from a strongly coupled quantum dot-cavity system
2008-11-21
A quantum dot strongly coupled to a photonic crystal has been recently proposed as a source of entangled photon pairs [R. Johne et al., Phys. Rev. Lett. 100, 240404 (2008)]. The biexction decay via intermediate polariton states can be used to overcome the natural splitting between the exciton states coupled to the horizontally and vertically polarized light modes, so that high degrees of entanglement can be expected. We investigate theoretically the features of realistic dot-cavity systems, including the effect of the different oscillator strength of excitons resonances coupled to the different polarizations of light. We show that in this case, an independent adjustment of the cavity resonances is needed in order to keep a high entanglement degree. We also consider the case when the biexciton-exciton transition is also strongly coupled to a cavity mode. We show that a very fast emission rate can be achieved allowing the repetition rates in the THz range. Such fast emission should however be paid for by a very complex tuning of the many strongly coupled resonances involved and by a loss of quantum efficiency. Altogether a strongly coupled dot-cavity system seems to be very promising as a source of entangled photon pairs.
Electron correlation in two-photon double ionization of helium from attosecond to FEL pulses
2009-01-27
We investigate the role of electron correlation in the two-photon double ionization of helium for ultrashort XUV pulses with durations ranging from a hundred attoseconds to a few femtoseconds. We perform time-dependent ab initio calculations for pulses with mean frequencies in the so-called "sequential" regime (photon energy above 54.4 eV). Electron correlation induced by the time correlation between emission events manifests itself in the angular distribution of the ejected electrons, which strongly depends on the energy sharing between them. We show that for ultrashort pulses two-photon double ionization probabilities scale non-uniformly with pulse duration depending on the energy sharing between the electrons. Most interestingly we find evidence for an interference between direct ("nonsequential") and indirect ("sequential") double photo-ionization with intermediate shake-up states, the strength of which is controlled by the pulse duration. This observation may provide a route toward measuring the pulse duration of FEL pulses.
The present article is the second out of three on a study of the sup 4 sup 0 Ca(e,e'x) reaction discussing the multipole decomposition of the measured cross sections and the analysis of angular correlations. The decomposition of the strongly overlapping E0, E1 and E2 giant resonance strengths using the (e,e'x; x=p,alpha) reaction in sup 4 sup 0 Ca is discussed for excitation energies between 10 and about 21 MeV. Two extraction methods are presented based on the variation of the form factors for the different multipoles. The resulting B(E1) strength distribution is in good agreement with (gamma,x) photoabsorption data. The summed B(E2) and B(E0) strength is highly fragmented and spread out over the energy region investigated. Microscopic continuum RPA calculations including the coupling of the basic particle-hole states to the low-lying surface vibrations are capable of reproducing the strength distributions quite accurately. Exhaustion of the energy-weighted sum rules (EWSR) for the various decay channels is presented. A complete decomposition of E0, E1 and E2 contributions in sup 4 sup 0 Ca is possible for (e,e'alpha) angular correlations populating the sup 3 sup 6 Ar ground state. Contrary to expectations, the form factors of isoscalar E0 and E2 strengths in the sup 4 sup 0 Ca(e,e'alpha sub 0) reaction exhibit increasing differences towards smaller momentum transfers. Angular correlations for proton decay into low-lying states of sup 3 sup 9 K are compared to a self-consistent continuum RPA calculation which allows a systematic description of the strong variations observed as a function of sup 4 sup 0 Ca excitation energy and momentum transfer. The success implies that direct knock-out models of the sup 4 sup 0 Ca(e,e'p) reaction are too simple. Furthermore, the shapes of the angular correlations seem to be determined largely by the final-state interaction, in particular by charge exchange reactions in the nuclear medium.
Cosmological Hydrogen Recombination: influence of resonance and electron scattering
2009-04-16
In this paper we consider the effects of resonance and electron scattering on the escape of Lyman alpha photons during cosmological hydrogen recombination. We pay particular attention to the influence of atomic recoil, Doppler boosting and Doppler broadening using a Fokker-Planck approximation of the redistribution function describing the scattering of photons on the Lyman alpha resonance of moving hydrogen atoms. We extend the computations of our recent paper on the influence of the 3d/3s-1s two-photon channels on the dynamics of hydrogen recombination, simultaneously including the full time-dependence of the problem, the thermodynamic corrections factor, leading to a frequency-dependent asymmetry between the emission and absorption profile, and the quantum-mechanical corrections related to the two-photon nature of the 3d/3s-1s emission and absorption process on the exact shape of the Lyman alpha emission profile. We show here that due to the redistribution of photons over frequency hydrogen recombination is sped up by DN_e/N_e~-0.6% at z~900. For the CMB temperature and polarization power spectra this results in |DC_l/C_l|~0.5%-1% at l >~ 1500, and therefore will be important for the analysis of future CMB data in the context of the PLANCK Surveyor, SPT and ACT. The main contribution to this correction is coming from the atomic recoil effect (DN_e/N_e~-1.2% at z~900), while Doppler boosting and Doppler broadening partially ca ncel this correction, again slowing hydrogen recombination down by DN_e/N_e~0.6% at z~900. The influence of electron scattering close to the maximum of the Thomson visibility function at z~1100 can be neglected. (abridged)
2010-01-01
InAs0.05Sb0.95 film with thickness of 100 mum has been grown by a modified LPE technique, and optical properties of the material have been investigated using spectroscopic-ellipsometry at room temperature within 1.5-4.5 eV. The dielectric function epsilon(E) spectra that show high-lying interband structure associated with E1, E1+DELTA1, and E2 transition have been observed and analyzed on the basis of a simplified model of the interband transitions. Results agree satisfactorily with the experimental data over the entire range of photon energies. The transition energies E1 and E2, the spin-orbit splitting energy DELTA1, and the broadening parameters are given, respectively
2007-07-15
The present work contains two parts. The first one is devoted to the investigation of mixed-symmetry structure in {sup 94}Mo and the second one to the astrophysical relevant line shape of the first excited 1/2{sup +} state in {sup 9}Be. In the first part of the thesis the nature of one- and two-phonon symmetric and mixed-symmetric 2{sup +} states in {sup 94}Mo is investigated with high-resolution inelastic electron and proton scattering experiments in a combined analysis. The (e,e') experiments were carried out at the 169 magnetic spectrometer at the S-DALINAC. Data were taken at a beam energy E e=70 MeV and scattering angles {theta}{sub e}=93 -165 . In dispersion-matching mode an energy resolution {delta}{sub E}=30-45 keV (full width at half maximum) was achieved. The (p,p') measurements were performed at iThemba LABS, South Africa, using a K600 magnetic spectrometer at a proton energy E p=200 MeV and scattering angles {theta}{sub p}=4.5 -26 . Typical energy resolutions were {delta}{sub E}{approx_equal}35 keV. The combined analysis reveals a dominant one-phonon structure of the transitions to the first and third 2{sup +} states, as well as an isovector character of the transition to the one-phonon mixed-symmetric state within the valence shell. Quantitatively consistent estimates of the one-phonon admixtures are obtained from both experimental probes when two-step contributions to the proton scattering cross sections are taken into account. In the second part of the thesis the line shape of the first excited 1/2{sup +} state in {sup 9}Be is studied. Spectra of the {sup 9}Be(e,e') reaction were measured at the S-DALINAC at an electron energy E e=73 MeV and scattering angles of 93 and 141 with high energy resolution up to excitation energies E{sub x}=8 MeV. The form factor of the first excited state has been extracted from the data. The astrophysical relevant {sup 9}Be({gamma},n) cross sections have been extracted from the (e,e') data. The resonance parameters of the first excited 1/2{sup +} state in {sup 9}Be are derived in a one-level R-matrix approximation. The deduced resonance parameters averaged over all available (e,e') data are E{sub R}=1.748(6) MeV and {gamma}{sub R}=274(8) keV However, the extracted B(E1) strength is a factor of two smaller than found in the latter indicating a violation of Siegert's theorem at the photon point. (orig.)
1995-12-31
We present the results of photoconductivity measurements of the resonant electron-phonon interaction in the middle of the Reststrahlen band using two-photon excitation with intense picosecond pulses with frequency around 143 cm{sup -1} (70 {mu}m). We use two photons rather than a single photon for the excitation of the resonant-polaron to avoid the problems of strong reflection and dielectric artifacts encountered in direct single-photon excitation in the Reststrahlen band. The sample is a 10 {mu}m thick Si-doped GaAs epitaxial layer on a 400 {mu}m semi-insulating GaAs substrate. The electronic levels of the Si shallow donor can be tuned by the application of a magnetic field. Intense tunable picosecond pulses with a frequency of around 143 cm{sup -1} from the Dutch free-electron laser FELIX are weakly focussed onto the sample, which is kept at 8 K. Electrons excited to the 3d{sup +2} state via the electric-dipole allowed two-photon transition out of the 1s{sub 0-} ground state, decay to the conduction band and give rise to an increase in the photoconductivity. The figure shows the energy-peak position of the 3d{sup +2} transition thus obtained as a function of the magnetic-field strength. The figure clearly shows the avoided crossing around the LO-phonon energy where the coupling shows the avoided crossing around the LO-phonon energy where the coupling between the 3d{sup +2} state and the LO phonon is strongest. Note that the data between 267 cm{sup -1} and 296 cm{sup -1} are extremely difficult to obtain with single-photon excitation because of their position in the middle of the Reststrahlen band.
Hints of the existence of Axion-Like-Particles from the gamma-ray spectra of cosmological sources
2009-05-21
Axion Like Particles (ALPs) are predicted to couple with photons in the presence of magnetic fields. This effect may lead to a significant change in the observed spectra of gamma-ray sources such as AGNs. Here we carry out a detailed study that for the first time simultaneously considers in the same framework both the photon/axion mixing that takes place in the gamma-ray source and that one expected to occur in the intergalactic magnetic fields. An efficient photon/axion mixing in the source always means an attenuation in the photon flux, whereas the mixing in the intergalactic medium may result in a decrement and/or enhancement of the photon flux, depending on the distance of the source and the energy considered. Interestingly, we find that decreasing the value of the intergalactic magnetic field strength, which decreases the probability for photon/axion mixing, could result in an increase of the expected photon flux at Earth if the source is far enough. We also find a 30% attenuation in the intensity spectrum of distant sources, which occurs at an energy that only depends on the properties of the ALPs and the intensity of the intergalactic magnetic field, and thus independent of the AGN source being observed. Moreover, we show that this mechanism can easily explain recent puzzles in the spectra of distant gamma-ray sources... [ABRIDGED] The consequences that come from this work are testable with the current generation of gamm a-ray instruments, namely Fermi (formerly known as GLAST) and imaging atmospheric Cherenkov telescopes like CANGAROO, HESS, MAGIC and VERITAS.
Search for low lying dipole strength in the neutron rich nucleus {sup 26}Ne
2007-05-15
Coulomb excitation of the exotic neutron-rich nucleus {sup 26}Ne on a {sup nat}Pb target was measured at 58 A.MeV in order to search for low-lying E1 strength above the neutron emission threshold. Data were also taken on an {sup nat}Al target to estimate the nuclear contribution. The radioactive beam was produced by fragmentation of a 95 A.MeV {sup 40}Ar beam delivered by the RIKEN Research Facility. The set-up included a NaI gamma-ray array, a charged fragment hodoscope and a neutron wall. Using the invariant mass method in the {sup 25}Ne+n channel, we observe a sizable amount of E1 strength between 6 and 10 MeV. The reconstructed {sup 26}Ne angular distribution confirms its E1 nature. A reduced dipole transition probability of B(E1)=0.49+/-0.16 e{sup 2}fm{sup 2} is deduced. For the first time, the decay pattern of low-lying strength in a neutron-rich nucleus is obtained. The results are discussed in terms of a pygmy resonance centered around 9 MeV.
B(E1) strengths from Coulomb excitation of {sup 11}Be
2007-06-28
The B(E1;1/2{sup +}->1/2{sup -}) strength for {sup 11}Be has been extracted from intermediate energy Coulomb excitation measurements, over a range of beam energies using a new reaction model, the extended continuum discretized coupled channels (XCDCC) method. In addition, a measurement of the excitation cross section for {sup 11}B + {sup 208}Pb at 38.6 MeV/nucleon is reported. The B(E1) strength of 0.105(12) e{sup 2} fm{sup 2} derived from this measurement is consistent with those made previously at 60 and 64 MeV/nucleon, in contrast to an anomalously low result obtained at 43 MeV/nucleon. By coupling a multi-configuration description of the projectile structure with realistic reaction theory, the XCDCC model provides for the first time a fully quantum mechanical description of Coulomb excitation. The XCDCC calculations reveal that the excitation process involves significant contributions from nuclear, continuum, and higher-order effects. An analysis of the present and two earlier intermediate energy measurements yields a combined B(E1) strength of 0.105(7) e{sup 2} fm{sup 2}. This value is in good agreement with the value deduced independently from the lifetime of the 1/2{sup -} state in {sup 11}Be, and has a comparable precision.
B(E1) Strengths from Coulomb excitation of 11Be
The B(E1;1/2{sup +}{yields} 1/2{sup -}) strength for {sup 11}Be has been extracted from intermediate energy Coulomb excitation measurements, over a range of beam energies using a new reaction model, the extended continuum discretized coupled channels (XCDCC) method. In addition, a measurement of the excitation cross section for {sup 11}Be+{sup 208}Pb at 38.6 MeV/nucleon is reported. The B(E1) strength of 0.105(12) e{sup 2}fm{sup 2} derived from this measurement is consistent with those made previously at 60 and 64 MeV/nucleon, in contrast to an anomalously low result obtained at 43 MeV/nucleon. By coupling a multi-configuration description of the projectile structure with realistic reaction theory, the XCDCC model provides for the first time a fully quantum mechanical description of Coulomb excitation. The XCDCC calculations reveal that the excitation process involves significant contributions from nuclear, continuum, and higher-order effects. An analysis of the present and two earlier intermediate energy measurements yields a combined B(E1) strength of 0.105(7) e{sup 2}fm{sup 2}. This value is in good agreement with the value deduced independently from the lifetime of the 1/2{sup -} state in {sup 11}Be, and has a comparable precision.
B(E1) Strengths from Coulomb excitation of 11Be
The B(E1;1/2{sup +}{yields} 1/2{sup -}) strength for {sup 11}Be has been extracted from intermediate energy Coulomb excitation measurements, over a range of beam energies using a new reaction model, the extended continuum discretized coupled channels (XCDCC) method. In addition, a measurement of the excitation cross section for {sup 11}Be+{sup 208}Pb at 38.6 MeV/nucleon is reported. The B(E1) strength of 0.105(12) e{sup 2}fm{sup 2} derived from this measurement is consistent with those made previously at 60 and 64 MeV/nucleon, in contrast to an anomalously low result obtained at 43 MeV/nucleon. By coupling a multi-configuration description of the projectile structure with realistic reaction theory, the XCDCC model provides for the first time a fully quantum mechanical description of Coulomb excitation. The XCDCC calculations reveal that the excitation process involves significant contributions from nuclear, continuum, and higher-order effects. An analysis of the present and two earlier intermediate energy measurements yields a combined B(E1) strength of 0.105(7) e{sup 2}fm{sup 2}. This value is in good agreement with the value deduced independently from the lifetime of the 1/2{sup -} state in {sup 11}Be, and has a comparable precision.
B(E1) Strengths from Coulomb excitation of 11Be
2007-03-06
The B(E1;1/2{sup +}{yields} 1/2{sup -}) strength for {sup 11}Be has been extracted from intermediate energy Coulomb excitation measurements, over a range of beam energies using a new reaction model, the extended continuum discretized coupled channels (XCDCC) method. In addition, a measurement of the excitation cross section for {sup 11}Be+{sup 208}Pb at 38.6 MeV/nucleon is reported. The B(E1) strength of 0.105(12) e{sup 2}fm{sup 2} derived from this measurement is consistent with those made previously at 60 and 64 MeV/nucleon, in contrast to an anomalously low result obtained at 43 MeV/nucleon. By coupling a multi-configuration description of the projectile structure with realistic reaction theory, the XCDCC model provides for the first time a fully quantum mechanical description of Coulomb excitation. The XCDCC calculations reveal that the excitation process involves significant contributions from nuclear, continuum, and higher-order effects. An analysis of the present and two earlier intermediate energy measurements yields a combined B(E1) strength of 0.105(7) e{sup 2}fm{sup 2}. This value is in good agreement with the value deduced independently from the lifetime of the 1/2{sup -} state in {sup 11}Be, and has a comparable precision.
B(E1) Strengths from Coulomb Excitation of 11Be
2007-03-16
The $B$(E1;$1/2^+\\to1/2^-$) strength for $^{11}$Be has been extracted from intermediate energy Coulomb excitation measurements, over a range of beam energies using a new reaction model, the extended continuum discretized coupled channels (XCDCC) method. In addition, a measurement of the excitation cross section for $^{11}$Be+$^{208}$Pb at 38.6 MeV/nucleon is reported. The $B$(E1) strength of 0.105(12) e$^2$fm$^2$ derived from this measurement is consistent with those made previously at 60 and 64 MeV/nucleon, i n contrast to an anomalously low result obtained at 43 MeV/nucleon. By coupling a multi-configuration description of the projectile structure with realistic reaction theory, the XCDCC model provides for the first time a fully quantum mechanical description of Coulomb excitation. The XCDCC calculations reveal that the excitation process involves significant contributions from nuclear, continuum, and higher-order effects. An analysis of the present and two earlier intermediate energy measurements yields a combined B(E1) strength of 0.105(7) e$^2$fm$^2$. This value is in good agreement with the value deduced independently from the lifetime of the $1/2^-$ state in $^{11}$Be, and has a comparable p recision.
Polariton optics of semiconductor photonic dots: weak and strong coupling limits
2004-09-08
We develop coherent optics of dipole-active, dispersionless excitons in spherical semiconductor photonic dots (PDs). In the absence of any incoherent scattering, both the strong and weak coupling regimes can intrinsically be realized simply by changing the parameters of the dot and surrounding medium. A criterion, which attributes the transition between these two regimes to a discrete topological change of the relevant dispersion curves, is found and approximated by an analytic expression. The transition depends upon the intrinsic radiative lifetime of the PD photon eigenstates, i.e. it is determined by the parameters of the structure (the oscillator strength of the exciton-photon interaction, PD radius and the ratio of the background dielectric constants inside and outside of the dot). We propose the use of high-precision modulation spectroscopy in order to visualize the above 'phase' transition between a well-developed polariton picture (the strong coupling regime) and weakly-interacting exciton and PD photon states (the weak coupling regime). It is shown that the radiative decay of optically dressed PD excitons, coherently distributed among the relevant PD eigenstates, is non-monotonous against the dot radius a: a size-dependent increase of the effective oscillator strength at small a saturates at a {approx} {lambda}, and with a increasing further towards a >> {lambda} the optical lifetime of excitons starts to increase proportionally to a, reflecting the ballistic escape of nearly bulk polaritons from the PD. The numerical simulations are scaled to dispersionless excitons in PDs fabricated from cyanine dye J aggregates.
Climbing the Jaynes-Cummings Ladder and Observing its Sqrt(n) Nonlinearity in a Cavity QED System
2009-02-17
The already very active field of cavity quantum electrodynamics (QED), traditionally studied in atomic systems, has recently gained additional momentum by the advent of experiments with semiconducting and superconducting systems. In these solid state implementations, novel quantum optics experiments are enabled by the possibility to engineer many of the characteristic parameters at will. In cavity QED, the observation of the vacuum Rabi mode splitting is a hallmark experiment aimed at probing the nature of matter-light interaction on the level of a single quantum. However, this effect can, at least in principle, be explained classically as the normal mode splitting of two coupled linear oscillators. It has been suggested that an observation of the scaling of the resonant atom-photon coupling strength in the Jaynes-Cummings energy ladder with the square root of photon number n is sufficient to prove that the system is quantum mechanical in nature. Here we report a direct spectroscopic observation of this characteristic quantum nonlinearity. Measuring the photonic degree of freedom of the coupled system, our measurements provide unambiguous, long sought for spectroscopic evidence for the quantum nature of the resonant atom-field interaction in cavity QED. We explore atom-photon superposition states involving up to two photons, using a spectroscopic pump and probe technique. The experiments have been performed in a circuit QED set up, in which ultra strong coupling is realized by the large dipole coupling strength and the long coherence time of a superconducting qubit embedded in a high quality on-chip microwave cavity.
Hyperfine splitting in hydrogen with form factors
2010-08-27
Proton structure corrections to the hyperfine splittings in hydrogen are evaluated using the Breit potential with electromagnetic form factors. In contrast to other methods, several new features emerge: the Breit potential with $q^2$-dependent form factors is just an extension of the standard Breit equation which gives the hyperfine Hamiltonian. Order $\\alpha^5$ corrections are obtained from a one-photon exchange amplitude and time-independent perturbation theory. Structure corrections to $D_{21} = 8 E^{2S}_{hfs} - E^{1S}_{hfs}$ start at order $\\alpha^6$. QED corrections are comparable to structure corrections which must be evaluated ab initio.
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