Tunable terahertz-wave generation from DAST crystal by dual signal-wave parametric oscillation of periodically poled lithium niobate

The first known demonstration of tunable terahertz-wave generation by difference-frequency generation of dual signal-wave quasi-phase-matched optical parametric oscillation was performed with periodically poled ${\mathrm{LiNbO}}_3$ (PPLN) with a series of gratings. An organic ionic salt, 4-dimethylamino-$N$-methyl-4-stilbazolium-tosylate (DAST), was used as a nonlinear crystal. A compact terahertz-wave source resulted, and changing the temperature of the PPLN permitted the wavelength to be varied from 120 to $160 \mathit{\mu }\mathrm{m}$. The wavelength could be tuned from 100 to $700 \mathit{\mu }\mathrm{m}$ by proper selection of combinations of periodically poled gratings.