Optimization of GdCOB:Nd and YCOB:Nd crystals for self-frequency doubling out of the principal planes

From the linear, nonlinear optical and laser properties of GdCOB:Nd and YCOB:Nd self-frequency doubling crystals, we have found that the slow laser wave at 1060 nm has a higher emission cross-section than the fast one in the whole locus of SH phase matching, meaning that self-frequency doubling should be possible on this whole locus. We have pointed out that the phase matching direction for maximum nonlinear optical coefficient d(eff) is far from the one for maximum laser emission cross-section. The question of optimum direction for the self-frequency doubling laser was solved with a complete laser modelling. The maximum value of the SH yield occurs at a polar angle theta = 68degrees for GdCOB:Nd, that is to say, close to the value of the optimum nonlinear optical coefficient d(eff). For YCOB:Nd, the polar angle at maximum SH yield is shifted at 72degrees, that is to say, towards the direction of the largest laser emission cross-section. In both cases, we can notice a larger "angular acceptance" on the locus of phase matching for the self-frequency doubling laser than for extra-cavity single pass frequency doubling.