Quantum fountain infrared light sources based on intersubband emissions in quantum wells

Abstract

Recent achievements on quantum fountain infrared sources relying on intersubband emission under optical pumping of coupled quantum well structures are reviewed. Population inversion can be achieved at mid-infrared wavelengths using a careful engineenng of the scattering rates between subbands. Observations of intersubband luminescences under either intersubband or interband optical pumping is reported. At low temperatures, the spontaneous emission is shown to result from direct optical excitation of the electrons in the upper subband. However, under interband excitation at room-temperature, the luminescence is the manifestation of the black-body emission of the two-dimensional electron gas. Population inversion at 77 K is then demonstrated for the first time using optical pumping by a free-electron laser. Large stimulated gains at 12.5 μm wavelength are reported. Lasing action appears to be feasible under infrared optical pumping.