Inverse distribution of hot electrons in a two-level quantum well with nonsymmetric scattering

We have studied the transient evolution of electrons distributed over two levels in a wide quantum well, with the two levels below the optical phonon energy, after an ultrafast interband excitation and cascade emission of optical phonons. If electrons are distributed near the top of the passive region, a temporal negative absorption appears to be dominant in the intersubband response. This is due to the effective broadening of the upper level state under the optical phonon emission. We have then considered the amplification of the ground mode in a THz waveguide with a multiquantum well placed at the center of the cavity. A huge increase of the probe signal is obtained, which permits the temporal stimulated emission regime of the photoexcited electrons in the THz spectral region.

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“…A similar description of the quasi-elastic relaxation in a two-level system was discussed in Ref. 8.…”

Section: Temporal Evolution Of the Electronic Distributionmentioning

confidence: 77%

“…The temporal evolution of the resonant absorption of the non-equilibrium electrons is described by the real part of the conductivity (see 8 and Appendix):…”

Section: Temporal Evolution Of the Electronic Distributionmentioning

confidence: 99%

Temporal stimulated intersubband emission of photoexcited electrons

2005

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“…The DQW's are described with an accuracy of the order T 2 for the case of independently-contacted DQW's with a thick barrier. The high-frequency response was considered self-consistently, with an accuracy of the order of e 2 terms, which has been successfully used both for a single QW with large-scale nonuniformities 15 and for a DQW structure ͑see Ref. 14͒; these results show that the approach used is valid for DQW structures with a broadening energy у0.1 meV).…”

Section: Discussionmentioning

confidence: 99%

“…The modal gain can be maximized if the DQW structure is placed along the central axis of a THz resonator with ideal mirrors at zϭϮL/2, where L is the width of the resonator, with dielectric permittivity ⑀. A simplified formula for the gain coefficient g is given for the fundamental mode by ͑see Ref 15. for details͒…”

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confidence: 99%

Negative intersubband absorption in biased tunnel-coupled wells

2003

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We investigate the use of intersubband transitions between two weakly coupled shallow quantum wells to generate terahertz radiation. The wells are designed for independent contacting and biasing. The maximum gain ͑absorption͒ scales with the wavefunction overlap and difference between the well carrier densities. The absorption line shape is studied taking into account the interplay between inhomogeneous and homogeneous broadening mechanisms, including both large-scale variations in the coupled levels and also short-range scattering. The intersubband transitions are strongly renormalized due to Coulomb interactions ͑depolarization and exchange effects͒. Population inversion can be achieved through independent variation of the upper and lower well Fermi energy with applied bias. Numerical estimates of the negative absorption coefficient are obtained using realistic parameters, indicating the possible application of such a THz resonator to achieve stimulated emission.

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“…This approximation is widely accepted because a detailed microscopical analysis of the relaxation does not basically affect the obtained results. An exact calculation including both scattering mechanisms can be found [10]. It would be possible to study electron-LO phonon interaction and elastic scattering as in [10], but under THz pump conditions.…”

Section: Introductionmentioning

confidence: 99%

Intersubband infrared absorption in stepped quantum wells under intense irradiation

Aceituno

Hernández‐Cabrera

Vasko

2005

J. Phys.: Condens. Matter

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The effect of an intense THz irradiation on the relative intersubband absorption of electrons in stepped quantum wells of GaAs-GaAlAs is theoretically studied. Analytical expressions for the induced current are obtained by means of the adiabatic and resonant approximations within the matrix density formalism. This method allows one to predict the presence of a marked fine structure on the absorption, together with a shift and broadening of the absorption peaks, when the pump intensity is around the megawatts level.

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Inverse distribution of hot electrons in a two-level quantum well with nonsymmetric scattering

Cited by 6 publications

References 22 publications

Temporal stimulated intersubband emission of photoexcited electrons

Temporal stimulated intersubband emission of photoexcited electrons

Negative intersubband absorption in biased tunnel-coupled wells

Intersubband infrared absorption in stepped quantum wells under intense irradiation

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