Fourier-Transform Spectrometer with a Terahertz-Wave Parametric Generator

A novel terahertz (THz)-wave spectrometer that combines a bright broad-band source of a laser-pumped THz-wave parametric generator (TPG) and a Martin-Puplett interferometer was developed. The TPG was based on stimulated polariton scattering via the lowest A1-symmetry mode in lithium niobate (LN). Broad-band THz-wave generation with nanosecond-pulse duration was achieved by single-pass pumping of the crystals with a Q-switched Nd:YAG laser. An array of silicon prisms was used to couple out THz waves efficiently. To optimize the output, various configurations of the LN crystals were examined. A peak power of 280 microwatts was achieved, and the spectral range extended from 30 to 120 cm-1 (0.9–3.6 THz), due to the first- and second-order Stokes scattering processes. The THz-wave spectrometer system with a nitrogen-purge unit was of tabletop size and had a maximum resolution of 0.025 cm-1 (750 MHz). THz spectroscopic data measured with the spectrometer were also presented.