Widely tunable high-power terahertz (THz) sources, highly sensitive detection technologies, and precise frequency measurement methods are essential and urgently needed in emerging areas, such as THz biophysics. The organic-crystal-based difference frequency generation (DFG) source (1–34 THz) with sensitive upconversion (UC) detection offers a promising and cost-effective platform but suffers from a limited sensitivity. In this paper, an optical parametric amplification (OPA) module is creatively employed in THz UC detection for better performance. The THz frequency at one of the emission peaks (∼26.2 THz) is measured from the perspective of DFG and UC, respectively, with a relative error of 0.01% level. A maximum signal gain of 23 dB with low noise figure is achieved in OPA at 26.2 THz using a commercial InGaAs PIN photodiode. An enhancement of two orders of magnitude on detection sensitivity is obtained. The minimum detectable pulse energy of THz wave is ∼5 fJ. The detection sensitivity is expected to be further improved by successfully applying more sensitive detectors after a series of optimizations.
Li et al. (Mon,) studied this question.