Two-color interband and intraband quantum well heterolaser

Abstract

A method of mid-infrared (ir) $(\ensuremath{\lambda}\ensuremath{\simeq}50\phantom{\rule{0.3em}{0ex}}\ensuremath{\mu}\mathrm{m})$ generation at an intraband transition in interband optical $(\ensuremath{\lambda}\ensuremath{\simeq}0.6\phantom{\rule{0.3em}{0ex}}\ensuremath{\mu}\mathrm{m})$ semiconductor quantum well (QW) heterolasers is considered. It is based on partial inversion of the intraband transition due to the electron population of its upper level, stimulated by a strong optical field simultaneously generated in the same device. In previous studies of the problem, the inhomogeneous broadening of this transition (i.e., its frequency dependence on the electron energies in the subbands that form it) was not taken into account. As a result, mid-ir generation was possible only under the condition of total (i.e., integrated over electron energies) inversion. In the present work it is shown that the inhomogeneous broadening of the intraband transition allows one to achieve mid-ir generation when it is inverted only in a narrow spectral range containing the interval where its interaction with the mid-ir mode has resonant character. At the same time, total inversion at this transition is absent. This circumstance makes it possible to significantly (by several times in comparison with previous estimates) reduce the threshold pumping current density for the start of mid-ir generation. As a result, this value proves to be in the experimentally achievable domain even at room temperature. This allows one to hope for the practical realization of a pulsed two-color optical and mid-ir laser based on a heterostructure with just one QW, employing simple and cheap injection pumping only, and working without any cooling.