OPTICAL SECOND HARMONIC GENERATION IN FORM OF COHERENT CERENKOV RADIATION FROM A THIN-FILM WAVEGUIDE

We report optical second harmonic generation in form of coherent Cerenkov radiation. The fundamental wave at 1.06 μm propagates in a thin-film optical waveguide which is simply a ZnS film vacuum-deposited on a single-crystal ZnO substrate. The nonlinear polarization excited in the substrate has a phase velocity exceeding that of radiation propagating freely in the substrate material. It thus acts as the source of the observed Cerenkov radiation.