Tunable ring cavity terahertz parametric oscillator with fixed emission direction

A tunable ring cavity terahertz parametric oscillator with fixed output direction is reported in this paper. The diamond-shaped Stokes beam resonator was designed for the adjustment of the Stokes beam propagation direction while the propagation direction of pump beam was adjusted by two reflection mirrors. The terahertz wave output direction can be always normal to the output surface by controlling the propagation directions of the pump and Stokes beams cooperatively during the frequency tuning in the range of 1.4–2.4 THz.