Periodic formation of transient population inversion for intersubband laser transitions in quantum wells.

A method of periodic short-term inversion for intersubband laser transitions in a quantum well with a repetition frequency of ∼1 GHz and inversion retention time ∼1 ps is suggested. The method is based on fast population of the upper transition level as a result of resonance tunneling of charge carriers from neighboring quantum wells as the electric field applied to the heterostructure is varied. As a consequence, the peak value of the population inversion can be as large, for example, as 8 × 1010 cm−2 for the transition corresponding to the wavelength λ ≈ 10 μm and 2 × 1010 cm−2 in the case of λ ≈ 25 μm. This method can be implemented at room temperature, which makes it attractive for fabrication of amplifiers of picosecond pulses for the middle and far infrared optical regions and the terahertz band. [ABSTRACT FROM AUTHOR]