Temporal stimulated intersubband emission of photoexcited electrons

TL;DR

This paper investigates the transient behavior of electrons in quantum wells after ultrafast excitation, revealing negative absorption effects and demonstrating potential for THz wave amplification via stimulated emission.

Contribution

It presents a novel analysis of electron dynamics in quantum wells and demonstrates stimulated emission in the THz range using a multiquantum well structure.

Findings

Negative absorption observed in intersubband response

Significant THz signal amplification achieved

Evidence of temporal stimulated emission in quantum wells

Abstract

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.