Intensity-dependent hot-phonon relaxation in ZnSe

We performed time-resolved anti-Stokes Raman-scattering experiments on ZnSe crystals using pump and probe techniques. To create non-equilibrium phonons we excited the ZnSe crystals at λ = 632.8 nm with an intense pump pulse with a pulse duration of about 4 ps, which leads to efficient two-photon absorption and therefore to the creation of free carriers. By relaxation to the band edge, the highly excited free carriers emit longitudinal optical (LO) phonons. By varying the time delay between the probe and the pump pulse, the dynamical behavior of the pump pulse-induced anti-Stokes Raman signal was studied. The results are discussed with respect to plasma effects influencing the dynamical behavior of the phonon lifetime in ZnSe.