We demonstrate a simple approach for a difference-frequency synthesiser within the terahertz domain. Two near-infrared CW diode lasers are frequency-locked to the resonances of a high finesse Fabry-Perot cavity using the Pound-Drever-Hall technique. Two acousto-optic modulators driven by RF synthesizers frequency-shift each diode laser and provide continuous tuning, modulation and switching capabilities for the difference-frequency. Terahertz-waves generated by heterodyne mixing in an ultrahigh-bandwidth photodetector are used to interrogate the rotational transitions in the ground state of the methyl-chloride.
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Aballea et al. (2008) studied this question.
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