Nonlinear Optics

Gallium-Selenide (GaSe) is a layered semiconductor which is characterized by a very high optical nonlinearity of second order (chi(2)). Optical second-harmonic generation (SHG) can therefore be accomplished with a weak cw laser with a power of a few milliwatts, if its beam is tightly focused onto the sample. The figures show Maker fringe curves (i. e., the second-harmonic signal as a function of the angle of incidence), which were recorded with low-power diode lasers of 1300 nm (left) and 1550 nm wavelength (right). The GaSe crystal was about 80 microns thick.