Efficient generation of annular cylindrical vector beams by refractive axicons with high-transmission thin-film retarders

Abstract

A new type of energy-efficient thin-film-coated (TF) conical optics is presented that combines annular beam shapers and cylindrical polarization converters to transform a linearly polarized laser beam into annular cylindrical vector beams. The main operational steps of the polarization converters include the generation of a circularly polarized vortex beam, the compensation of a quarter-wave shift between its p- and s-polarized components, and the summation of these components, with the last two steps being carried out simultaneously by means of such key elements as conically illuminated high-transmission TF retarders. Three optical configurations are considered and analyzed, of which the TF retarders are located on the conical surfaces of two refractive beam-shaping axicons. The total light throughput of such configurations approach 100% and they are suitable for operation at deep UV wavelengths and high power density. As potential elements of these configurations, five TF retarders are designed and optimized at a wavelength of 266 nm. Numerical simulations and comparison of the angular and spectral characteristics of these TF retarders confirm that they comply with the tolerances on the acceptable deviations of axicon wedge angles and wavelengths of typical high-power CW lasers with the above wavelength. Also presented are the results of a tolerance analysis of the TF retarders with respect to their TF thicknesses.