Efficient upconversion by a frequency factor between two and three using an optical parametric oscillator

We present the theory of a scheme for frequency up-conversion from pump frequency /spl omega//sub p/ to a desired frequency /spl omega//sub d/ between 2/spl omega//sub p/ and 3/spl omega//sub p/. The proposed device consists of three nonlinear crystals in series inside a cavity resonating light at a signal frequency /spl omega/s. Sum-frequency generation (SFG) in the first crystal produces the desired radiation, /spl omega//sub s/+/spl omega//sub p/=/spl omega//sub d/. Second-harmonic generation (SHG) in the second crystal doubles the frequency of the residual pump, 2/spl omega//sub p/=/spl omega//sub h/, while the signal passes through unaffected. Optical parametric oscillation (OPO) in the third crystal generates the signal and idler frequencies, /spl omega//sub h/=/spl omega//sub s/+/spl omega/. A plane-wave analysis predicts a quantum efficiency close to 30% over an extended range of pump intensity. Iteration of the plane-wave solutions over many passes yields dynamics very similar to that recently calculated for the SFG-OPO device. As in that device, a small detuning of the SFG interaction enlarges the dynamic range yielding stable operation. Highest efficiency occurs when /spl omega//sub i/ is at the low-frequency end of the OPO crystal transmission window. As an example, we consider a device using a noncritically phase-matched KTP SFG crystal, a quartz crystal polarization rotator, an angle-tuned KTP SHG crystal, and a noncritically phase-matched LiNbO/sub 3/ OPO crystal. This device is designed to convert /spl lambda//sub p/=1.064 /spl mu/m to /spl lambda//sub d/=0.455 /spl mu/m. We calculate a power conversion efficiency as great as 73%.<
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