Conversion of Laguerre–Gaussian beams into Gaussian beams of reduced focal spot by use of a circular echelon

Abstract

Abstract In this article we present numerical calculations for the diffraction of a Laguerre–Gaussian laser beam (TEMp0), with “0” radial mode number and “p” azimuthal mode number, by circular echelon (CE) which is an annular multi-phase level Diffractive Optical Element (DOE) with a phase variations of Δφ. We apply the super resolution technique for transforming a symmetrical TEMp0 Laguerre–Gauss beam into a quasi Gaussian intensity distribution. The beam shaping is modeled on the p light rings of the incident beam. We present the diffracted intensities distributions in the back focal plane of a converging lens for different mode TEM01, TEM02, TEM03, TEM04, TEM05. The advantage of this technique is that the rectified TEMp0 beam at focus has a focal volume very smaller than that of a Gaussian beam and smaller than the rectified TEMp0 beam at focus of an annular binary Diffractive Optical Element (DOE) and its intensity is greater than that of an annular binary (DOE), also its fabrication is simpler.