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^-2 intensity. A nonlinear pulse propagation model, including linear dispersion and 4PA was used to obtain the 4PA coefficients from measurements. The intensity-dependent effective 4PA coefficients vary from 2.6 × 10^-4 to 65 × 10^-4 cm⁵GW^-3 in GaP, and from 3.5 × 10^-4 to 9.1 × 10^-4 cm⁵GW^-3 in ZnTe. The anisotropy in 4PA was shown in GaP. The knowledge of 4PA coefficients is important for the design of semiconductor photonics devices.