Photorefractive and charge transport properties of the organic crystal 4-N,N-dimethylamino-4'-N'-methylstilbazo toluene-p-sulfonate

4-N,N-dimethylamino-4'-N'-methylstilbazolium toluene-p-sulfonate (DAST) is an organic salt that consists of the nonlinear optical stilbazolium cation and the tosylate anion needed to induce a noncentrosymmetric packing. It shows an enormous potential for electro-optical applications in the near infrared range due to an almost parallel alignment of the highly nonlinear chromophores along the polar a-axis (the angle between the molecular charge transfer axis and the polar axis is of about 20/spl deg/). In spite of the constant improvement of the photorefractive sensitivity of organic crystals since 1990, the obtained values are still far smaller than the theoretical expectation for optimized organic molecular crystals, which predicts a gain of several tens per centimeter for a response time of less than a second at an illumination intensity of 1 W/cm2. In order to improve the photorefractive sensitivity of organic crystals, the photogeneration and charge transport properties of the charge carriers are of prime importance and are investigated for the case of the organic salt DAST.