Two-photon absorption in semiconductors with picosecond laser pulses

Single pulses from a well-calibrated mode-locked YAlG:Nd laser have been used to measure the two-photon absorption coefficient at 1.064 μm in several semiconductors. The materials studied are four direct-gap semiconductors, GaAs, CdTe, ZnTe, and CdSe, and one indirect-gap semiconductor, GaP. The results for the direct-gap semiconductors are interpreted with respect to the imaginary part of the third-order nonlinear susceptibility ${\chi }_{1111}^{\mathrm{}\left(3\right)\mathrm{}}(-\omega ,\omega ,\omega ,-\omega )$. An anisotropy of the two-photon absorption coefficient is observed in GaAs.