Narrowing of oscillation linewidth in a quasi-monolithic THz-wave parametric oscillator

We have demonstrated a quasi-monolithic THz-wave parametric oscillator (TPO) to confer more stability, a lower threshold, and more compact size on THz-wave generating devices. In this report, we describe narrow linewidth generation in a quasi-monolithic TPO. The cavity configuration was designed so that the noncollinear phase-matching condition was satisfied in the crystal. A 5 mol% MgO:LiNbO3 crystal within dimensions of 15 mm X 20 mm with three surfaces for total reflection was used as a nonlinear optical crystal. The quasi-monolithic TPO in a ring-cavity configuration consisted of a nonlinear optical crystal and a super-mirror that reflected the idler beam (lambda > ca. 1067 nm) and transmitted the pump beam (1064 nm). We obtained narrow oscillation linewidth of < 760 MHz at 1.6 THz of THz-wave radiation. The low threshold of the oscillation was around 5.4 mJ/pulse.