Optical design and enhanced output of a surface-emitted THz-wave parametric oscillator

High-power tunable terahertz wave(THz-wave) radiation was parametrically generated via a surface-emitted THz-wave parametric oscillator(TPO) pumped by a multi-longitudinal-mode Q-switched Nd:YAG laser. The effective parametric gain length under the condition of noncollinear phase matching was calculated to optimize the parameters of TPO. The THz-wave radiation from 0.77 to 2.83 THz was obtained. The maximum THz-wave output is 347.8 nJ/pulse at 1.78 THz when the pump power density is 222.3 MW/cm2, corresponding to the energy conversion efficiency of 3.9110-6. The far-field divergence angle of THz-wave radiation is 0.020 4 rad at vertical direction and 0.006 8 rad at horizontal direction.