Gain without inversion in a biased superlattice

TL;DR

This paper investigates gain without inversion in a biased superlattice, revealing negative absorption below resonance and potential THz spectral gain in low-doped GaAs superlattices.

Contribution

It provides a theoretical analysis of intersubband transitions showing gain without inversion beyond the Born approximation, including effects of broadening mechanisms.

Findings

Negative absorption occurs below resonance.

Detectable THz gain in low-doped GaAs superlattices.

Spectral dependencies influenced by broadening mechanisms.

Abstract

Intersubband transitions in a superlattice under homogeneous electric field is studied within the tight-binding approximation. Since the levels are equi-populated, the non-zero response appears beyond the Born approximation. Calculations are performed in the resonant approximation with scattering processes exactly taken into account. The absorption coefficient is equal zero for the resonant excitation while a negative absorption (gain without inversion) takes place below the resonance. A detectable gain in the THz spectral region is obtained for the low-doped $GaAs$-based superlattice and spectral dependencies are analyzed taking into account the interplay between homogeneous and inhomogeneous mechanisms of broadening.