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We report the wavelength dependencies of the two- and three-photon absorption coefficients of undoped GaAs in the spectral range 1.3-3.5 microm, as well as nonlinear refractive index n2 in the range 1.7-3.25 microm. 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.

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The authors demonstrate an efficient room temperature source of terahertz radiation using femtosecond laser pulses as a pump and GaAs structures with periodically inverted crystalline orientation, such as diffusion-bonded stacked GaAs and epitaxially grown orientation-patterned GaAs, as a nonlinear optical medium. By changing the GaAs orientation-reversal period ͑504-1277 m͒, or the pump wavelength ͑2 -4.4 m͒, we were able to generate narrow-bandwidth ͑ϳ100 GHz͒ terahertz wave packets, tunable between 0.9 and 3 THz, with the optical-to-terahertz photon conversion efficiency of 3.3%.

We developed a tabletop source of intense, narrow band terahertz pulses via type-II difference-frequency generation in ZnTe crystal using two linearly chirped and orthogonally polarized optical pulses. The pulse energy is in the range of 1-3 nJ depending on the variable pulse duration from 1 to 5 ps. The amplitude of electric field reaches ϳ10 kV/ cm. The central frequency of the spectrum is continuously tunable from 0.3 to 2.5 THz with the bandwidth at 0.2-0.5 THz.