Generation of tunable Fourier-transform-limited terahertz pulses in $4-N,N$-dimethylamino-$4′-N′$-methyl stilbazolium tosylate crystals

We report difference-frequency generation (DFG) of widely tunable, pulsed, Fourier-transform-limited terahertz radiation (bandwidth of $∼10MHz$⁠, peak power up to $∼400μW$⁠) from pulse-amplified near-infrared $(λ∼800nm)$ laser radiation using a crystal of the organic salt $4-N,N$-dimethylamino-$4′-N′$-methyl stilbazolium tosylate (DAST) cut along the $b$ axis to fulfill the phase-matching condition. The broad tunability and narrow bandwidth of the terahertz radiation generated by DFG in DAST are illustrated by a single scan of the terahertz spectrum of $H2O$ from 0.1 to 11 THz, and a recording of the absorption spectrum of a pure rotational transition of HF near 5 THz.