Observation of the forbidden second-harmonic generation in resonance with 2PWannier exciton in ZnSe thin films

Publisher Website
Google Scholar
Abstract
We have observed for the first time a drastic enhancement of the normally forbidden second-harmonic generation signal when twice the incident-photon energy is resonant with the excitation energy of a 2P exciton in thin ZnSe crystals. Measurements were performed, using a titanium sapphire laser, at 4.2 K in such a geometrical configuration, x(zz, x or y) or x(yy, x or y)z, that transitions are forbidden by the usual selection rules. The results are shown to be well accounted for in the framework of a time-dependent perturbation formalism.