We report the study of optically induced terahertz (THz) electromagnetic radiation from (110) oriented zinc-blende crystals. This work extends our previous studies of (100) and (111) GaAs. Excellent agreement between calculated results and experimental data indicates that, under conditions of moderate optical fluence and normal incidence on the unbiased sample, second-order optical rectification is the major nonlinear process that generates THz radiation.

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We present recent experimental results of difference-frequency generation (DFG) and sum-frequency generation (SFG) from zincblende materials. We measure the radiation field of difference-frequency generation and the radiation intensity of sum-frequency generation versus crystallographic orientation and fundamental photon energy. The simultaneous measurement of the angular dependence of polarized DFG and SFG is well characterized by the bulk second-order nonlinearity calculation. Pronounced resonant behaviors near the GaAs band gap for both radiations (DFG and SFG) are compared.

Phosphorus is one of several dopants that electronically compensate the native deep donor responsible for the yellow coloration observed in bismuth silicon oxide (BSO). Low-temperature optical absorption measurements of a series of Czochralski-grown P-doped BSO crystals show that ∼0.1–0.15 at. % P is needed in the sample to fully remove the yellow coloration. The absorption cutoff in the fully compensated P-doped sample was at 3.2 eV while compensated Al- and Ga-doped samples cutoff at 3.35 eV. Excitation at 10–15 K with near band-edge light produces photochromic absorption bands. In the lightly-doped (partially bleached) samples these bands were identical to those observed in undoped BSO. In the fully bleached sample a new spectrum was observed. Its major contribution was a band centered near 1.8 eV with a weaker absorption in the blue-green. By comparison with the spectra observed in undoped and in Al-doped material before and after photoexcitation it is believed that the 1.8 eV band is due to the [PO4]− center and that the broad 2.45 eV band observed in Al- and Ga-doped BSO is due to the [BiO4]0 center.