Measurement of four-photon absorption in GaP and ZnTe semiconductors.

Intensity-dependent effective four-photon absorption (4PA) coefficients in GaP and ZnTe semiconductors were measured by the z-scan method using pump pulses of 1.75 µm wavelength, 135 fs duration, and up to 500 GWcm intensity. A nonlinear pulse propagation model, including linear dispersion and 4PA was used to obtain the 4PA coefficients from measurements.

High-energy terahertz pulses from semiconductors pumped beyond the three-photon absorption edge.

A new route to efficient generation of THz pulses with high-energy was demonstrated using semiconductor materials pumped at an infrared wavelength sufficiently long to suppress both two- and three-photon absorption and associated free-carrier absorption at THz frequencies. For pumping beyond the three-photon absorption edge, the THz generation efficiency for optical rectification of femtosecond laser pulses with tilted intensity front in ZnTe was shown to increase 3.5 times, as compared to pumping below the absorption edge.