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THz radiation is detected by a low-temperature-grown GaAs (LT-GaAs) photoconductive antenna probed with a 1.55 μm probe laser. The detection efficiency is found to be approximately 10% of that obtained with a 780 nm probe. From the nonquadratic dependence of photoconductivity on laser intensity, two-step photoabsorption mediated by midgap states in LT-GaAs is suggested, instead of the two-photon absorption, as the primary process for the photoconductivity.
Tani et al. (Mon,) studied this question.