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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.

This is the first report of single-cycle terahertz (THz)-wave pulse generation with a wide band (over 6 THz) and a high dynamic range (over 70 dB) using an organic nonlinear optical crystal, 4-dimethylamino-N′-methyl-4′-stilbazolium tosylate (DAST), and the prism-coupled Cherenkov phase-matching method. The prism-coupled approach allowed the use of a DAST crystal as a Cherenkov-type emitter for reduced light absorption by the crystal, resulting in the generation of single- and half-cycle THz pulse shapes, which were detected using dipole and bow-tie antennas, respectively. The resulting THz pulse generation is suitable for various THz-wave application technologies, such as tomography.

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