Probing quantum efficiency by laser-induced hot-electron cooling

Experimental evidence of a physical phenomenon characteristic of semiconductor lasers, i.e., cooling of the electrons above the threshold for stimulated emission, is reported. We show that this effect is directly related with the internal quantum efficiency (ηint), which is one of the central physical quantities in the theory of semiconductor lasers. As a model system we selected the terahertz quantum-cascade laser that is particularly suitable for the investigation of nonequilibrium electronic ensembles. The reported procedure for the assessment of ηint can be easily extended to other model systems, enlightening the relevance of including hot-electron distributions in semiconductor laser modeling.