Enhanced conversion efficiency for harmonic generation with double resonance.

The idea of using a resonant cavity to enhance conversion efficiency in cw second-harmonic generation was first discussed by Ashkin et al.,' who found that the conversion efficiency can be greatly increased by resonating either the fundamental or the harmonic field. Because of its simplicity, the scheme of employing a resonator to build up the fundamental power is the one most widely used in practice and has recently led to the achievement of high cw conversion efficiency. 2 -7 For such a scheme, the conversion efficiency Y7 for the ratio of generated second-harmonic power P2,out to the injected fundamental power P1,j1n is found from the relation2' 4' 7