Abstract
A coherent terahertz (THz) wave can be generated by difference frequency generation (DFG) using nonlinear optical crystals. DFG has a potential advantage of wide tunability achieved by a proper selection of the DFG crystal and input wavelengths. In this paper, we present the latest progress in widely tunable THz-wave generation from 0.3 to 6.5 THz using DAST crystals. As a dual-wavelength light source for DFG, we employed a KTP optical parametric oscillator in the 1100-1200 nm range pumped at 532 nm. Using a thick DAST crystal more than 1 mm, maximun THz-frequency was limited to 0.6 THz. However, using thin DAST crystals less than 0.3 mm, a peak power of more than 10 mW were successfully generated at 2.5 and 4.3 THz. In spite of the present nanosecond-pulse operation, a compact system of widely tunable THz-waves, including a diode-pumped Q switched Nd:YAG laser and a pyroelectric detector, could be useful in THz-imaging and spectroscopic applications.
