Showing papers on "Free electron model published in 1983"
TL;DR: In this paper, a new type of infrared photodetector using free electron absorption in a heavily doped GaAs/GaAlAs quantum well structure has been demonstrated, and preliminary results indicate a strong response in the near infrared with a responsivity conservatively estimated at 200 A/W.
Abstract: A new type of infrared photodetector using free electron absorption in a heavily doped GaAs/GaAlAs quantum well structure has been demonstrated. Preliminary results indicate a strong response in the near infrared with a responsivity conservatively estimated at 200 A/W. The structure can potentially be tailored during fabrication for use in several infrared bands of interest, including the 3 to 5 micron band and the 8 to 10 micron band.
145 citations
TL;DR: In this paper, a preliminary experimental investigation of the generation of second-harmonic photons from the interaction of free electrons with an intense laser beam has been performed, showing reasonable agreement with both classical and quantum electrodynamics.
Abstract: A preliminary experimental investigation of the generation of second-harmonic photons from the interaction of free electrons with an intense laser beam has been performed. Second-harmonic photons with a wavelength of 530 nm generated from the interaction of free electrons with 1060-nm photons from a neodymium-glass laser are implied by observing Doppler-shifted photons with wavelengths of 490 and 507 nm. The observed photon wavelengths result from a Doppler shift of the laser photon wavelength as viewed in the rest frame of the electrons, combined with a Doppler shift of the second-harmonic photon emitted from 1600- and 500-eV electrons. Comparison of experimental results with those predicted by cross sections, derived from classical and quantum electrodynamics, shows reasonable agreement with both theories. Although second-harmonic photons are created, the dynamics of second-harmonic-photon generation (accelerated electron motion due to the electromagnetic field or actual two-photon interaction with the electron) cannot be resolved p without further experiment.
62 citations
62 citations
TL;DR: In this paper, it was shown that the signal velocity of a free electron is the same as its group velocity, which in turn is also similar to that of a classical particle particle particle of the same energy.
Abstract: There has recently been a growth in interest in electron tunnelling through barriers, and in particular in the question of whether it is possible to talk of a tunnelling time and, if so, what is it? A brief account of a study of the signal velocity of wavepackets travelling into a rectangular barrier was given recently, and the present paper is an extended version of this theory. In particular it is shown that the signal velocity of a free electron is the same as its group velocity, which in turn is the same as that which a classical particle particle of the same energy would have. It is also shown that when the wavepacket enters a classically forbidden region the signal velocity continues to have a meaning, and indeed a pulse-like wavefunction travels very much like a light pulse in a dispersive and attenuating medium. The expression for the signal velocity is symmetrical with respect to the barrier height, so that pulses well below the barrier travel faster, though with greater attenuation, than pulses near the top of the barrier. This result agrees with conclusions reached by some other workers. It is also shown that an electron responds to an accelerating field in the barrier as would be expected for a classical particle. It is argued that the not uncommon statement that the non nor eigenstates of a free particle describe a beam of particles is incorrect for electrons, for such a solution can at most describe two electrons. The theory indicates that by using orthogonal wavepackets it is possible to construct many-electron wavefunctions which do describe beams of electrons, and then free electrons travel with the group (and signal) velocity.
52 citations
TL;DR: In this paper, a nonwiggler free electron laser, operating in uniform guide magnetic field, is analyzed and the amplifier problem is solved self-consistently on the basis of the kinetic theory.
Abstract: A nonwiggler free electron laser, operating in uniform guide magnetic field, is analyzed. The amplifier problem is solved self-consistently on the basis of the kinetic theory. It is shown that the asymmetry in the azimuthal distribution of the electrons' momentum leads to a coupling between the transverse and the space-charge modes. This, in turn, enhances the gain in the amplifier. In the case of a cold beam, with the electrons gyrating coherently, the spatial growth in the collective nonwiggler free electron laser (FEL) is comparable to that found in conventional free electron lasers operating in similar regimes.
39 citations
TL;DR: In this article, the collective interaction in a free electron laser with a combined helical wiggler and uniform axial guide field is presented in the low-gain regime, and substantial discrepancies are found between the results for the realizable and ideal wigglers, and a selection rule relating the TE and TM ln modes with resonant amplification at the l th harmonic of the FEL Doppler upshift.
Abstract: The collective interaction in a free electron laser with a combined helical wiggler and uniform axial guide field is presented in the low-gain regime. The wiggler model we employ is fully self-consistent and includes all transverse inhomogeneities. The analysis is performed for a free electron laser (FEL) amplifier in which the radial dependence of the radiation is treated using both the TE and TM waveguide modes. Substantial discrepancies are found to exist between the results for the realizable and ideal wigglers, and a selection rule relating the TE ln and TM ln modes with resonant amplification at the l th harmonic of the FEL Doppler upshift.
39 citations
TL;DR: In this article, the authors measured the birefringence changes induced in LiNbO3:Fe by a light beam to determine the photovoltaic characteristics such as the saturation value of space charge field, dielectric relaxation time, the probability φ of creating a free electron by an absorbed photon and the mean migration length L of the electron.
Abstract: Birefringence changes induced in LiNbO3:Fe by a light beam have been measured to determine the photovoltaic characteristics such as the saturation value of space charge field, dielectric relaxation time, the probability φ of creating a free electron by an absorbed photon and the mean migration length L of the electron. These quantities are determined for different wavelengths covering the region 400–600 nm. The product φL that determines the photorefractive sensitivity of the material increases with decreasing wavelength. This increase is largely due to the increase of φ, the variation of the migration length being relatively small.
38 citations
TL;DR: In this article, an analysis of the free-electron-laser (FEL) oscillator startup problem in the linear regime is presented, where the wiggler field is assumed to occupy a portion of the finite $Q$ resonator.
Abstract: An analysis of the free-electron-laser (FEL) oscillator startup problem in the linear regime is presented. The model is spatially one dimensional, though many important three-dimensional effects are included heuristically. The electron beam consists of pulses of arbitrary shape separated by approximately twice the radiation transit time. The small gain per pass approximation is employed in deriving an energy rate equation, which describes the evolution of the radiation pulses within the resonator. The wiggler field is assumed to occupy a portion of the finite $Q$ resonator. In the energy rate equation, the spontaneous (incoherent) radiation term is represented by a source matrix, while the stimulated (coherent) radiation term is represented by a gain matrix. The effect of small variations in the mirror separation are investigated in the context of laser lethargy. Our analysis suggests possible methods which could substantially shorten the startup times in FEL oscillators. Finally, our results are compared with the FEL oscillator experiments performed at Stanford University.
38 citations
TL;DR: In this paper, the influence of an intense laser field on the motion of an electron in the effective lattice potential was investigated and it was shown that, for moderately intense fields, the band gap decreases linearly with increasing laser intensity.
36 citations
TL;DR: In this article, photo-injection experiments show that the energy V 0 of the quasi-free electron in methane is negative at all densities from the dilute gas to the solid with a minimum roughly coinciding with the mobility maximum.
TL;DR: In this article, a Lagrangian formalism is used to describe the dynamics of the interacting electron beam and optical wave in a single pass, and several laser magnet designs are compared under the same formalism.
Abstract: In a free-electron laser oscillator, both the amplitude and frequency of the optical field are free to evolve. We use a Lagrangian formalism to describe the dynamics of the interacting electron beam and optical wave in a single pass. The character of the evolution over many passes is controlled by the design of the undulating magnetic field in the free-electron laser interaction region. Several laser magnet designs are presented under the same formalism and compared: the undulator, the tapered undulator, the optical klystron, and transverse gradient (''gain-expansion'') undulator. For each of these designs we numerically calculate the gain as a function of optical amplitude and frequency. These ''gain surfaces'' are used to infer a variety of properties of oscillator evolution and clearly demonstrate the relative merits of each magnet design.
TL;DR: In this article, the differential cross section for photon scattering from relativistic polarized free electrons in motion is derived, and the results provide an alternative check on recent work carried out using a quasi-relativistic Hamiltonian.
Abstract: The differential cross section for photon scattering from relativistic polarized free electrons in motion is derived. The calculation extends early results from electrons at rest. It is argued that the present derivation is required for use in bound-state spin-dependent Compton scattering from polarized electrons. The results provide an alternative check on recent work carried out using a quasi-relativistic Hamiltonian.
TL;DR: In this paper, the electronic specific heat coefficient ψ can be described by the free electron density of states with an electron-phonon mass enhancement factor 1 + λ = 1.24.
TL;DR: In this paper, a model for electron transfer across a modulation doped (Al,Ga)As/GaAs heterostructures is proposed to calculate the change in free electron concentration in the As.
Abstract: When modulation doped (Al,Ga)As/GaAs heterostructures are exposed to light, the interface electron concentration and in most cases the mobility increases substantially for lattice temperatures below ∼100 K. A substantial part of the increase is persistent and attributed to the excitation of electrons from a donor–vacancy complex in the (Al,Ga)As. The change in the free electron concentration in the (Al,Ga)As is calculated using a recently developed model for electron transfer across a modulation doped heterojunction. The persistent increase in the free electron concentration is used as a measure of the trap concentration. The magnitude of the photoconductivity response decreased with increasing growth temperature in the range 580–750 °C. The dependence on Al mole fraction was studied for 0.16≤x≤1.0 and found to be a maximum for x∼0.3.
TL;DR: In this paper, the problem of oscillator evolution and mode competition in free electron lasers is studied, where Relativistic quantum field theory is used to calculate electron wave functions, the angular distribution of spontaneous emission and the transition rates for stimulated emission and absorption in each mode.
Abstract: The problem of oscillator evolution and mode competition in free electron lasers is studied. Relativistic quantum field theory is used to calculate electron wave functions, the angular distribution of spontaneous emission, and the transition rates for stimulated emission and absorption in each mode. The photon rate equation for the weak-field regime is presented. This rate equation is applied to oscillator evolution with a conventional undulator, a two-stage optical klystron, and a tapered undulator. The effects of noise are briefly discussed.
TL;DR: In this article, the authors measured the optical absorption of submonolayer silver films deposited on a fused quartz ATR prism for the spectral range between 1.5 and 6.0 eV.
TL;DR: In this article, the main focus was on the propagation propagation of pulse propagation and the main influence on the electrability of the propagation of the pulse propagation with respect to a comparison with Stanford's experimental data.
Abstract: The main fea tures re levan t t o pulse propagation i n f r e e elect r o n l a s e r s a r e discussed together with a comparison t o t h e Stanford os c i l l a t o r experimental data .
TL;DR: In this article, the competition between electron-electron and the electron-lattice interactions is studied with the 4-site-4electron model characterized by B (half of the band width), U (on-site Coulomb repulsion) and S (lattices relaxation energy).
Abstract: Competition between the electron-electron and the electron-lattice interactions is studied with the 4-site-4-electron model characterized by B (half of the band width), U (on-site Coulomb repulsion) and S (lattice relaxation energy). In the whole range of B , U and S the lowest adiabatic potential is exactly calculated, and all of its minima and their existence conditions are found. The absolute minimum is the antiferromagnetic phase (with antiferromagnetic spin correlation but no lattice distortion) or the charge density wave phase (with alternating lattice distortion). The first-order transition between them occurs along a line close to U = S . Electronic and structural properties of these two phases are studied in detail. System size dependence of the phase diagram is discussed, with the emphasis on the difference between 4 n - and (4 n +2)-electron systems.
TL;DR: In this article, the resistivity, Hall coefficient and magnetoresistance of thin bismuth films were measured at various temperatures (80 − 300 K) and thicknesses (0.1 − 3 μm).
TL;DR: In this paper, the authors used free electron theory to estimate the Ba-O charge transfer and made a semiquantitative evaluation of the Ba dipole, assuming the Helmholtz equation applies.
TL;DR: In this article, a mechanism is proposed to interpret the experimental results which show a reduction in the short wavelength output power when gyroresonance is reached, and the presence of an axial magnetic field in a free electron laser around gyroreonance introduces a strong long wavelength Raman backscattering instability which itself gives rise to electron trapping and causes the desired short wavelength radiation to saturate earlier than unmagnetized free electron lasers.
Abstract: A mechanism is proposed to interpret the experimental results which show a reduction in the short wavelength output power when gyroresonance is reached. The presence of an axial magnetic field in a free electron laser around gyroresonance introduces a strong long wavelength Raman backscattering instability which itself gives rise to electron trapping and causes the desired short wavelength radiation to saturate earlier than unmagnetized free electron lasers.
TL;DR: In this paper, a wiggler-free free electron laser operating in a waveguide was analyzed by using a single particle treatment, and the use of either a TE or a TM mode was shown to enhance the gain for a resonant frequency much higher than the cyclotron frequency.
Abstract: A wiggler‐free free electron laser operating in a waveguide is analyzed by using a single particle treatment. The use of either a TE or a TM mode is shown to enhance the gain for a resonant frequency much higher than the cyclotron frequency. It is demonstrated that a source of a submillimeter radiation, based on this analysis, may have output power comparable to that of a wiggler‐type free electron laser.
TL;DR: In this paper, a simple analytical expression of the scattering cross-section was demonstrated independently by a thermodynamical method and by a stochastic formulation, and a numerical simulation of the fluctuating electron concentration leads to a numerical crosssection profile which agrees with the theoretical expression.
TL;DR: In this article, the magnetoresistance and cyclotron resonance of a two-dimensional sheet of electrons localized above liquid and solid hydrogen surfaces is investigated at the frequency of 20 GHz.
Abstract: The magnetoresistance and cyclotron resonance of a two-dimensional sheet of electrons localized above liquid and solid hydrogen surfaces are investigated at the frequency of 20 GHz. It is found that the effective electron mass relevant to the motion along the surface is close to the free electron mass. The electron mean free path is determined by collisions with defects of the solid hydrogen surface. For 5≲T≲12 K the electron mobility was ∼8×104/T cm2/V sec, with 20% accuracy, for all the specimens investigated. ForT≲5 K the mobility follows the law
$$\mu \propto 1/\sqrt {{\text{W}}_{\text{e}} } $$
, wherew
e
is the mean electron energy. The numerical values of the electron mobilities for different specimens differ by factors up to five, and forT≲1 K they fall within within the range 2×104 to 105 cm2/V sec. The experimental results indicate that the solid hydrogen surface has a terrace structure with flat sections about 10−5 cm in size. During the investigation of electrons localized above a saturated helium film wetting the solid hydrogen, we observed a shift of the resonance to weaker magnetic fields, which amounts to ∼100% at a pressing field of ∼103 V/cm. It is shown that this shift can be explained by the terrace structure of the substrate.
01 Jan 1983
TL;DR: In this paper, an atmospheric pressure air breakdown plasma using the emission from a short-pulse millimeter-wave free-electron maser is used to demonstrate frequency tunability over the range 50-100 GHz, via breakdown standing wave patterns, and very high peak power.
Abstract: Production of an atmospheric pressure air breakdown plasma using the emission from a short‐pulse millimeter‐wave free‐electron maser is used to demonstrate frequency tunability over the range 50–100 GHz, via breakdown standing wave patterns, and very high peak power.
TL;DR: In this paper, a commercial Auger spectrometer was used to analyse the surface composition and to measure the electron loss spectra of eight different samples, and the electron primary energies were 100 and 300 eV.
TL;DR: In this article, Ag-Ge and Au-Ge amorphous alloy films have been prepared by co-evaporation on cold (15-20 K) substrates under ultra-high vacuum for Ge concentrations between 20 and 40 at.% by resistance versus temperature measurements during annealing and room-temperature electron diffraction experiments.
Abstract: Ag—Ge and Au—Ge amorphous alloy films have been prepared by co-evaporation on cold (15–20 K) substrates under ultra-high vacuum for Ge concentrations between 20 and 40 at.%. Changes in short-range order for samples with Ge concentrations larger than 30 at.% were studied by resistance versus temperature measurements during annealing and room-temperature electron diffraction experiments. The d.c. electrical resistivity and the optical properties measured in situ at the deposition temperature are examined in detail. The Drude model with a constant relaxation time is found to reproduce the optical data at low energies satisfactorily. Deviations from this model at higher energies, as well as discrepancies between the average effective number of conduction electrons per atom and the predictions of a rigid-band model, are attributed to s, p-d hybridization. Interband transitions are also discussed.