Spontaneous parametric down-conversion in an organic DAST crystal

Nonlinear optical effect of spontaneous parametric down-conversion (SPDC) is widely used to produce entangled photon pairs for quantum information research and applications. We report on SPDC in 4-N, N-dimethylamino-4'-N'-methyl-stilbazolium tosylate (DAST) crystals. While being an early-phase exploration, the experimentally measured yield of the down-converted photons at the optical telecom wavelength is already comparable to that in the state-of-the-art periodically poled potassium titanyl phosphate (KTP) crystal. It hints at a greater potential being available, especially in its crystal orientation with an order of magnitude higher nonlinear coefficient, which is unfortunately not accessible in the present setup. The findings make the DAST system a promising candidate for entangled photon sources at telecom wavelengths.