Terahertz-induced lensing and its use for the detection of terahertz pulses in a birefringent crystal

We demonstrate terahertz-induced lensing (TIL), the focusing and defocusing of an ultrashort “probe” laser pulse induced by a collinearly traveling terahertz pulse in an electro-optic crystal. The intensity change on the axis of the probe beam after the crystal is shown to be linear with the terahertz (THz) electric field and can thus be used to measure the THz wave form. We show that the sensitivity of TIL is comparable to conventional electro-optic sampling, with the advantage of being applicable to all classes of electro-optic crystals, including strongly birefringent ones. The better sensitivity of TIL is demonstrated using the highly birefringent organic salt DAST (4-$\mathrm{N,N-}\mathrm{dimethylamino}{\text{-4}}^{\prime }{\mathrm{-N}}^{\prime }$ -methyl stilbazolium tosylate).