Running electric field gratings for detection of coherent radiation

A technique for the room temperature electro-optic detection of coherent low-frequency radiation, typically in the far infrared or terahertz (THz) range, is proposed. It relies on a longitudinally running electric field grating probed by phase-matched Raman–Nath diffraction of a higher frequency wave. The expected probe wave diffracted intensity is background-free and is proportional to the desired signal intensity. As an example, we present model calculations for the probing of monochromatic THz radiation using the organic crystal 4-N,N-dymethylamino-4′-N′-methyl-stilbazolium 2,4,6-trimethylbenzenesulfonate as nonlinear optical sensor material, for which new measurements of the refractive index and absorption up to a frequency of 11 THz are presented.