We report the observation of terahertz-field-induced second-harmonic (TFISH) generation in a beta barium borate (β-BBO) crystal based on a four-wave-mixing process. Using the conventional second-harmonic generation in the β-BBO crystal as a local oscillator, the crossed term between the TFISH and the local oscillator is proportional to the terahertz field. This phenomenon is used for coherent detection of intense terahertz waves, where a good linear response is observed for terahertz fields up to 160 kV/cm. In comparison, deviation from linear response and strong waveform distortion are observed when a 0.5-mm-thick ZnTe detector is used to characterize the same terahertz field.
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Chen et al. (2009) studied this question.
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