Optical Parametric Oscillation with Intracavity Sum-Frequency Generation

We present theoretical calculations of an optical parametric oscillator (OPO) containing, in addition to the OPO crystal, a crystal for intracavity sum-frequency generation (SFG). The latter crystal combines light at the pump frequency ω p with light at the OPO signal frequency ω s to produce the desired frequency ω d = ω p + ω s . Only the frequency ω s oscillates in the cavity. This system is modeled in the plane-wave approximation for both spatial orderings of the crystals. The pump power is ultimately converted to the desired radiation, to idler radiation of frequency ω i =2ω p – ω d , and to cavity losses at frequency ω s . Since the ω i and ω d radiation grows from zero on each pass, changes in the cavity length do not produce interference effects. The choice of crystal for the OPO is limited by the requirement that this crystal transmit the long-wavelength idler. With proper choice of design parameters, little pump power remains unconverted by the two crystals over an extended range of the incident pump intensity. In steady-state operation the ratio η of the photon flux emitted at ω d to the photon flux incident at ω p can be nearly 0.5.