New data on the doubling of the emission frequency of a high-power neodymium laser in KDP crystals

A theoretical analysis shows that, in the case of nonzero first-harmonic radiation divergence, the eta(z) and eta(W) relationships (where eta is the efficiency of conversion to the second harmonic, z is the crystal length, and W is the intensity of first-harmonic radiation) for the frequency conversion of Nd-laser radiation in a KDP crystal have the same qualitative character as in the plane-wave case. This points to the existence of an optimal crystal length at a given power density and divergence of the fundamental emission. These results are confirmed by experiments performed with KDP crystals of high optical quality.