Terahertz Kerr effect (TKE) in a water film . (a) Diagram of the experimental setup. An intense THz pulse generated from an organic crystal DAST (4-N, N-dimethylamino-4-N-methyl-stilbazolium tosylate) is focused onto a free-standing water film. The THz field-induced Kerr effect is detected by an optical probe. (b) TKE with different THz peak field strengths. Inset: THz field strength dependence.