Random frequency accessible broad tunable THz-wave source using phase-matched DAST crystal DFG

Abstract

Ultra broad band (from 1.5 to 37 THz) THz-wave generation using difference frequency generation (DFG) in an organic 4-dimethylamino-N-methyl-4-stilbazolium tosylate (DAST) crystal was demonstrated. A DAST crystal is one of the promising materials for efficient and high power THz-wave generation, because of its very high nonlinearity and low refractive index dispersion between the near infrared region and the THz-wave region. We can use DAST's highest nonlinear component of, d11 (about 230pm/V), to generate THz-wave with by means of DFG, because the co-linear phase matching condition of the Type0 configuration is satisfied. We constructed a dual-wavelength optical parametric oscillator (OPO) with two KTP crystals pumped by frequency doubled Nd:YAG laser. Each KTP crystal was set on a Galvano scanner and the angle of each crystal was controlled independently. The OPO has a tunable range from 1300 - 1900 nm, results in an ultra broad tunable range of the THz-wave. We successfully generated ultra broad tunable THz-wave just using only one DAST crystal without any change of the experimental setup, except the computer controlled Galvano scanner angle change. The Hhighest THz-wave energy of 10 nJ was obtained at around 26 THz region under 2 mJ of pumping energy. And also, the THz-wave source can access an arbitral THz frequency at for every pulse (50 Hz at present). The Galvano scanner has a 1 kHz of responsibility response and we would obtain 1 msec of frequency access speed.