High-Speed High-Resolution Terahertz Spectrometers

We demonstrate and characterize both asynchronous optical sampling terahertz time-domain spectroscopy (AOS THz-TDS) and terahertz frequency comb spectroscopy (TFCS) as high-speed, high-resolution terahertz (THz) spectroscopy. Two mode-locked femtosecond (fs) lasers with slightly different repetition frequencies are used without a mechanical delay stage to generate and detect THz pulses, respectively. Repetition frequencies of the two fs lasers are stabilized by use of two phase-locked loops sharing the same reference oscillator, respectively. For AOS THz-TDS, the difference frequency between the repetition frequencies is optimized and a signal-to-noise ratio is measured as a function of a measurement time. Spectra of THz frequency comb and its individual modes are measured from TFCS. A spectral resolution of 100 MHz is obtained in the both types of spectroscopy.