Terahertz-frequency upconversion detection with organic crystal DSTMS

As a derivative of the famous organic crystal 4-N, N-dimethylamino-4'-N' -methyl-stilbazolium tosylate (DAST), 4-N, N-dimethylamino-4'-N'-methyl-stilbazolium 2,4,6-trimethylbenzenesulfonate (DSTMS) with improved properties should be a promising nonlinear medium for terahertz (THz) wave upconversion (UC) detection. To the best of our knowledge, the present work demonstrates this ability of DSTMS for the first time. An optically pumped system integrating a tunable source and a UC detection segment is self-constructed. The frequency-dependent UC responsivity of this system is illustrated over a wide range of 2.23-30 THz. When comparing the two above-described crystals, DSTMS exhibits superior performance to the original DAST, achieving 73.9% coverage of this band. The sensitivities are improved by 5 dB at 3.7 THz and by 8 dB at 18.4 THz. The matches and shifts of the absorption centers between the two crystals are clearly shown. As explained theoretically, the optimization of the molecular structure of DSTMS reduces its THz absorption effect and enhances the UC responsivity. This work also provides an effective approach for studying the active properties of nonlinear crystals at room temperature and for supporting directional selection processes in the field of crystal synthesis.