Formation of high-power hollow Bessel light beams

An investigation was made of the possibility of conversion of high-power laser beams into hollow Bessel beams with the first maximum in the radial field distribution in the form of a ring and a slight variation of the field in the direction of propagation. An analysis was made of the influence of real conditions during formation of such beams on their parameters. The limits were found on the divergence of the intial laser radiation and on the characteristics of one of the conversion components (phase screw). These limits had to be kept for the formation of the field distribution in the form of a hollow tube. Experiments were carried out with the aid of a beam former consisting of an axicon and a phase screw, and also with the aid of kinoform elements equivalent to a combination of an axicon and a phase screw. The results confirmed the validity of the theoretical analysis. Hollow beams were formed with radial distributions described by the Bessel functions of the first, second, and fifth orders. The beam length was 20 cm and the diameters of the principal maxima were 20 – 60 μm.