Continuous wave phase-locked optical parametric oscillator as a tunable source for terahertz radiation

We describe the operation of a cw phase-locked doubly resonant optical parametric oscillator that is suitable as a tunable optical source for the generation of terahertz radiation. A highly stable cw optical parametric oscillator has been constructed with a tuning range of several THz in the signal- idler difference frequency. By phase locking this difference frequency to a microwave source, either directly or with the use of a terahertz optical frequency comb generator, the parametric oscillator serves as a precisely tunable difference-frequency source. In one experiment, we phase locked the parametric oscillator at a signal-idler difference frequency of 665 GHz. In a second experiment, we measured a signal-idler difference frequency of 1.45 THz with the use of a diode-pumped YAG laser.