Improved idler beam quality via simultaneous parametric oscillation and signal-to-idler conversion.

We report on an improvement of idler beam quality in a singly resonant optical parametric oscillator (OPO), where the resonant signal is converted to the idler via an additional difference frequency generation (DFG) process. The two processes are phase matched simultaneously by a quasi-periodically poled nonlinear crystal. Whereas back-conversion of the signal and idler to the pump frequency distorts the idler beam in a standard OPO, in a quasi-periodic OPO the DFG process reduces the signal intensity, leading to suppression of back-conversion and, hence, improvement in idler beam quality.

Dislocation parity effects in crystals with quadratic nonlinear response.

The effect of edge topological dislocations on the phase matching spectrum of quadratic nonlinear photonic crystals was studied theoretically and experimentally. We have found that the parity of the dislocation's topological charge governs the transfer of energy between an input wave and its second harmonic. A dislocation with an odd topological charge nulls the efficiency of the otherwise optimal phase matched wavelength, whereas high conversion is now achieved at new wavelengths that exhibited low efficiency without the dislocation.