Design of a GaN∕AlGaN intersubband Raman laser electrically tunable over the 3–5μm atmospheric transmission window

Design results aimed at achieving tunable high-temperature operation in the 3–5μm atmospheric transmission window are presented for the intersubband Raman lasers based on GaN∕AlGaN coupled quantum wells. The ultrafast longitudinal-optical-phonon (LO-phonon) scattering in GaN∕AlGaN quantum wells (QWs) can be used for the rapid depopulation of the lower laser state, while the large LO-phonon energies (∼90meV) allow for a design to minimize the thermal population of the lower laser state, and are therefore beneficial for obtaining high-temperature operation. The Raman gain is proportional to the difference between the virtual lifetime of the upper laser state and the effective lifetime of the lower laser state instead of the real lifetimes. The advantage is that these lifetimes can be tuned with the detuning of the pump photon energy from the subband energy separation. At a fixed pumping wavelength of 2.7μm, the tuning range of 3.6–5.2μm is predicted with a moderate Raman gain of at least 100∕cm as the electric field is varied. Furthermore, the output power of this laser is unlikely to saturate because of the intrinsically short intersubband lifetimes in the GaN-based QWs.