Stimulated two-photon emission in bulk CdSe

While two-photon emission processes are firmly established in atomic physics, their observation and use in semiconductor physics remains elusive. Here, we experimentally investigate stimulated two-photon emission in photoexcited bulk CdSe and identify requirements for the observation of stimulated two-photon emission. In particular, this process requires population inversion as well as two-photon transition energies close to the bandgap energy. In any regime investigated in the present study, net optical gain is not achieved, as the free-carrier absorption intrinsically linked to the photoexcitation completely masks the two-photon gain. The results are well in line with a recent study on nondegenerate versions of two-photon emission in GaAs and place clear limits for the practical use of two-photon emission in optically excited semiconductors.