Far-infrared second-harmonic generation and pulse characterization with the organic salt DAST

We generated the second harmonics of pulses in the far-infrared region $\left(30–55 \mathit{\mu }\mathrm{m}\right)$, using the organic salt dimethylamino-4-$N$-methylstilbazolium tosylate (DAST). We demonstrate that DAST can be used to characterize ultrashort pulses in a spectral region where no other materials are available. To illustrate the need for such characterizations, we show the effects of propagation through air on the shape of ultrashort far-infrared pulses.