Multiphoton absorption and nonlinear refraction of GaAs in the mid-infrared

We report the wavelength dependencies of the two- and three-photon absorption coefficients of undoped GaAs in the spectral range 1.3 – 3.5 um, as well as nonlinear refractive index n2 in the range 1.7 – 3.25 um. The data were obtained by using the single-beam Z-scan method with 100-fs-long optical pulses. Anisotropy of the three-photon absorption coefficient was observed and found to be consistent with the crystal symmetry of GaAs.