Determination of the Quality Parameters of Higher-Order Bessel Light Beams

A method is proposed for evaluating the quality of higher-order Bessel light beams (BLBn, order n > 0) by analyzing digital computer images of two-dimensional transverse intensity distributions. One image is sufficient to assess the quality in a specific transverse cross section of a BLBn. Algorithms are described which ensure correct implementation of this method: an algorithm for evaluating the position of the axis of an annular beam based on cluster analysis, an algorithm for estimating an initial approximation of the conicity parameter when approximating experimental diametral intensity distributions by the square of a Bessel function based on analyzing the spectral power density of the diametral distribution. The proposed method and algorithms are implemented in the form of an extension of a software package for analyzing the quality of Bessel light beams. The software package is used to test the method experimentally to analyze a BLB1 produced with the aid of KTP (KTiOPO4) and KGW (KGd(WO4)(2)) crystals from a study of a semiconductor laser module (SCLM) and a helium-neon laser (HNL). It is shown that the beam formed by the HNL retains a constant radius along different azimuthal directions while the conformity to the shape of an ideal BLB1 is lost over a larger distance from the axicon than the SCLM, but also loses its constant intensity more rapidly along different azimuthal directions in the first annulus.