Periodic Transient Inversion at Intersubband Laser Transitions in Quantum Wells in an External Electric Field

A method of the periodic transient inversion of an intersubband laser transition in a quantum well (QW) with the repetition rate < 1 GHz and the inversion lifetime of ~ 1 ps is suggested. The method is based on the rapid population of the upper transition level via carrier resonant tunneling from an adjacent QW under not an adiabatic (as in previous studies of the problem), but a quick biased electric field change. It allows one to speed up this process significantly (by an order of magnitude) employing the same fields, and thereby, reach a peak inversion of 4 times 10¹⁰ cm^-2 at room temperature for a transition corresponding to lambda lsim 10 mum. This makes it possible to achieve the fivefold power amplification of picosecond mid-infrared pulses using three consequent synchronized QW heterostructures (the cascade scheme). The possibility of operating at room temperature renders this method attractive for various applications.