Characteristics of the terahertz radiation from single crystals of N-substituted 2-methyl-4-nitroaniline

Terahertz (THz) radiation was generated via optical rectification from orga nic single crystals, i.e. N-substituted (N-benzyl, N-diphenylmethyl, and N- 2-naphthylmethyl) derivatives of 2-methyl-4-nitroaniline (MNA), and it was detected by means of the electro-optic sampling method. The intensity and t he spectrum of the THz radiation were compared with those of ZnTe and DAST (N, N-dimethylamino-N'-methylstilbazolium p-toluenesulphonate) crystals. Th e integrated intensity of the THz radiation from the N-benzyl-MNA crystal w as two thirds of that for the ZnTe crystal, the best-known practical THz em itter, and was as intense as that for the DAST crystal, the best organic TH z emitter ever studied. The spectrum of the ZnTe crystal extended to 3 THz, while that of the N-benzyl MNA and DAST crystals dropped off around 2.5 TH z. The THz radiation intensities from all of the organic crystals were comp ared quantitatively, on the basis of the consideration of molecular arrange ments in the crystals. It was suggested that the absorption due to low-freq uency phonon modes affected both the intensity and the spectral band shape of the THz radiation.