Terahertz-wave generation from 4-dimethylamino-N′-methyl-4′-stilbazolium p-bromobenzenesulfonate crystal: Effect of halogen substitution in a counter benzenesulfonate of stilbazolium derivatives

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We have developed a technique to grow 4-dimethylamino-N′-methyl-4′-stilbazolium p-bromobenzenesulfonate (DASB) with a halogen (bromine) substituent in the anion for THz-wave generation. The bulky DASB single crystals, typically measuring 3×3×0.2mm3, are grown from a methanol solution by the slow-cooling method over a 5-week period. Compared with 4-dimethylamino-N′-methyl-4′-stilbazolium tosylate (DAST), the DASB crystal showed high transmittance at around 3THz and in the region above 100THz. Using the difference frequency generation process, we can obtain a broadband THz-wave between 2 and 25THz from a DASB crystal. Moreover, the output THz-wave power between 2.5 and 5.5THz generated from DASB is high, confirming that halogen substitution in the anion of stilbazolium derivatives enables efficient THz-wave generation in the region between 2.5 and 5.5THz.