In the approximation of a given field the problem is studied of the effect of the basic radiation amplitude profile in the necking plane of the focusing system on the second harmonics generation efficiency. It is shown that the results correspond most closely to the set problem, which were obtained for the second harmonics generation in conditions, when the influence of the pin-hole aperture effect is either -partly weakened (cylindrical focusing) or excluded completely (90 synchronism). It is found that in both cases the maximal second harmonics generation efficiency at the minimal power density of the main radiation is provided by laser beams with the Gaussian amplitude distribution in the cross-section.
amplitude profile; cylindrical focusing; second harmonic generation; power density