Bessel and Bessel vortex beams generated by blunt-tip axicon

Abstract

A theoretical prediction of the propagation characteristics of Laguerre--Gaussian beams after passing through a blunt-tip axicon is presented. An ideal axicon generates theoretically perfect diffraction-free and smooth-on-axis intensity Bessel beams, while experiments and calculations show that a zeroth-order Bessel beam deviates from its perfect behavior. Strong intensity modulation occurs due to interference around the center of the beam. The origin of these oscillations should be explored to increase the quality of beam shaping. This research shows that these oscillations can be reduced by stopping the beam center for a small portion or by optimizing input beam parameters. On the other hand, since they have singularity at the beam center, higher-order Bessel beams would be affected less by the bluntness of the axicon. In order to prove this idea, a series of calculations with wavelengths of 1030, 515, and 343 nm were conducted. The tip of the axicon was modeled as a hyperbola with a base angle of 0.5$^{\circ}$. Our calculations indicate that zeroth-order Bessel beams are much more sensitive than the higher-order Bessel beams to axicon bluntness. Moreover, not only the axicon geometry and wavelength of the illuminating light, but also the input beam parameters are quite important when enhancing the quality of beam shaping.