Organic Nonlinear Optical Single-Crystalline Thin Film Grown by Physical Vapor Deposition for Terahertz Generation

There are a number of advantages to terahertz (THz) waves by Cherenkov phase matching using a nonlinear optical (NLO) crystal; however, a thin crystal of micrometer-scale must be grown to satisfy the optimal phase matching conditions. Inorganic crystals with well-developed crystal growth and processing techniques have been widely used to date; however, THz wave generation with improved efficiency in the broadband region could be achieved with a single-crystalline thin film of an organic NLO material with a large NLO coefficient. Here, the growth of a crystalline thin film with a size of several microns using a very simple method is reported. Physical vapor deposition is used to grow a crystal of the organic nonlinear material 2-(3-(4-hydroxystyryl)-5,5-dimethylcyclohex-2-enylidene) malononitrile (OH1). This method is much simpler than the conventional crystal growth method. Additionally, the OH1 single-crystalline thin film grown by physical vapor deposition has a better crystalline character than a bulk OH1 crystal grown by the solution method. The OH1 single crystal grown by this technique demonstrates efficient THz wave generation and low absorption of THz waves by the crystal.