Generation of the second harmonics of Bessel light beams in a KTP crystal

Theoretical and experimental investigations were made of the characteristic features of doubling the frequency of Bessel light beams by the oe-e interaction in a KTP crystal. All possible and scalar interactions of planewave components of Bessel beams were observed experimentally. The spatial structure of the second harmonic in the far zone consisted of a central spot and a concentric ring, The diffraction divergence of the central beam was weak (similar to 1.7 mrad), The energy conversion efficiency was similar to 21% for a Bessel beam, which was three times higher than the efficiency of conversion of the initial laser beam. A theoretical model was based on representation of the field of the second harmonic as a superposition of Bessel beams, which provided a correct description of the observed spatial and energy characteristics of the second harmonic.