Publications Details
Phase correction in two-crystal optical parametric oscillators
The effect of the pump, signal, and idler wave phases on three-wave nonlinear parametric mixing is investigated in a series of single-pass- gain experiments. Measurements are made with two angle-tuned KTP crystals in a 532 nm pumped, walkoff-compensated, optical parametric amplifier that is seeded by an 800 nm cw diode laser. In one of the measurements the second crystal is orientated to have its effective nonlinearity deff. of opposite sign to that of the first crystal, so that all mixing that occurred in the first crystal is canceled by the second when the phase mismatch Δkcrystal 1 = Δkcrystal 2 = 0. Efficient two-crystal amplification is subsequently restored by selecting the correct phase relationship for the three waves entering the crystal by inserting a dispersive plate between the crystals. The experimental results are explained in a straightforward manner with diagrams involving the three input wave polarizations. These results demonstrate that walkoff-compensated geometries require phase correction to achieve efficient mixing in the second crystal whenever the nonlinear interaction involves two extraordinary waves (e-waves). One practical application of this work may be lower oscillation thresholds and enhanced performance in walkoff-compensated optical parametric oscillators which use two e-waves.