Phase-matching, nonlinear optics frequency mixing

For these reasons many modern nonlinear frequency-doubling or mixing devices, in particular, optical parametric oscillators, use quasi phase matching [5.244,5.245]. 

For these reasons many modem nonlinear frequency-doubling or mixing devices, in particular, optical parametric oscillators, use quasi phase matching [5.251,5.252]. Gallium arsenide has a very high nonlinear coefficient and a wide transparency range of 0.7—17 xm. It is therefore very attractive for widely tunable optical parametric oscillators in the mid-infrared. It is now possible to fabricate orientation-patterned GaAs which can be used as quasiphase-matched material. 

---