Tunable and narrow-linewidth THz difference frequency generator with DAST crystal pumped by dual-seeded KTP optical parametric oscillator

A tunable and narrow-linewidth terahertz (THz) difference frequency generation (DFG) with DAST crystal was demonstrated based on near infrared pump in this paper. A dual-seeded KTP optical parametric oscillator (OPO) was constructed as a pump source for DFG. The THz frequency can be continuously tuned in the range of 1.1-8.0 THz. The maximum signal-to-noise ratio (SNR) of 40.5 dB was obtained at 4.315 THz. The linewidth of the output THz-wave was estimated to be less than 473 MHz by fitting transmission spectrum of CO gas at 1800Pa pressure around 49.93 cm^-1 with the Voigt gas model. Furthermore, the THz spectral measurements of the mixture of CO gas and water vapor in air were in good agreement with their absorption lines in Hitran database. Additionally, the measurement of the transmission spectroscopy and the absorption coefficient of white PE tablet were demonstrated in wideband THz range. Such wide tunable THz source with narrow linewidth has good potential in THz high-precision spectroscopic detection.