30 of fig2 the smaller overlap of circular spot shapes 50 and 52 of laser beams exiting nonlinear crystal 30 produces higher order laser modes resulting in laser output that departs from a gaussian shape the greater overlap of elliptical spot shapes 54 and 56 results in laser output more closely of gaussian shape fig5 is graph showing the ellipticity of laser beam 34 propagating in wedge faceted nonlinear crystal 30 u2032 as a function of entrance angle 30 for four refractive indices n equal to 1 4 1 6 1 8 and 2 0 fig5 indicates that a larger entrance angle u03b8 imparts to an input laser beam greater eccentricity of its elliptical spot shape for each selected combination of pulse repetition rate pulse width and average power there can be determined an optimal combination of the spot shape of the input beam nonlinear crystal length walk off angle and entrance angle u03b8 the entrance angle u03b8 is operationally effective for any wavelength of incident light beam fig5 reveals that an entrance angle u03b8 of greater than about 10 u00b0 and preferably between about 10 u00b0 and about 40 u00b0 provides an advantageous greater effective interaction length because of the reduced walk off effect higher harmonic conversion efficiency and higher beam quality can be achieved with a smaller.