Effect of partial mode locking on second harmonic generation

Theoretical and experimental investigations were made of the effect of partial locking of "domain"-type axial and transverse modes on the characteristics of second harmonic generation. An analysis was made in the constant field approximation using a second-order correlation function formalism and the reverse effect of the second harmonic was allowed for by a numerical technique using a digital computer. It was shown that partial locking of these modes increases the conversion efficiency by a factor of 8–14 compared with single-frequency conditions for nonlinear crystals having small anisotropy angles. It is noted that in nonlinear crystals having large anisotropy angles the efficiency of second harmonic generation by a fundamental-frequency beam with partially locked transverse modes is reduced substantially.