We report the THz generation using optical rectification process in an indigenously grown organic salt 4-N, N-dimethylamino-4'-N'-methyl-stilbazoliumtoyslate (DAST). A 60 fs, 1 kHz optical parametric amplifier, tunable between 0.8 and 1.6 mm range was employed to generate THz radiation. It is observed that the THz signal is accompanied with weak second harmonic signal of pump wavelength. The conversion efficiency (eta) of generated THz is 0.0161%. The radiation generated from DAST crystal is only THz signal, which is confirmed theoretically by choosing the crystal thickness is equivalent to be its optimum coherence length. In addition, we have selected two rotational lines i.e. J = 19, 58 of pure N2O gas by using 0.5 and 1.5 THz band pass filters for recording the time resolved photoacoustic (PA) spectra at 1 atm pressure for the first time. (C) 2016 Elsevier B.V. All rights reserved.