Widely tunable terahertz-wave generation in an organic crystal and its spectroscopic application

TLDR

The study investigates terahertz‑wave generation via difference‑frequency mixing in a DAST crystal, combining theoretical analysis and experimental validation. A dual‑wavelength optical parametric oscillator employing two KTP crystals, tunable from 1300 to 1450 nm and pumped by a 10‑ns diode‑pumped, frequency‑doubled Nd:YAG laser, served as the tunable light source. The system produced tunable THz radiation from 2 to 20 THz, delivering 82 nJ at 11.6 THz and 110 nJ at 19 THz with a 1‑mm DAST crystal, and the resulting spectroscopic measurements of a PTFE sheet matched those from a conventional far‑infrared spectrometer.

Abstract

Terahertz (THz)-wave generation using difference-frequency mixing in an organic 4-N, N-dimethylamino-4′-N′-methyl-stilbazolium tosylate (DAST) crystal was investigated theoretically and experimentally. We developed a dual-wavelength optical parametric oscillator (OPO) with two KTiOPO4 crystals as the input light source. This oscillator has a tunable range from 1300–1450 nm and is pumped by a diode-pumped, frequency-doubled, Q-switched Nd:YAG laser with a pulse duration of 10 ns. Widely tunable THz waves ranging from 2 to 20 THz were generated from DAST crystals with 0.5- and 1-mm thickness using the OPO. THz output energies of 82 nJ (peak power of 10.3 W) at 11.6 THz and 110 nJ (peak power of 13.8 W) at 19 THz were obtained with a 1-mm-thick DAST crystal. Using a tunable THz-wave system consisting of the THz source and a pyroelectric detector, THz spectroscopic data for a polytetrafluoroethylene sheet were obtained and were comparable to data obtained from a conventional far-infrared spectrometer.