High quality diameter-variable hollow annular beam generated by two round-tip axicons

Abstract

The hollow annular beam generated by an axicon-telescope has advantaged properties such as that the beam inner diameter and ring width are controllable in precision illumination applications. However, the hollow beam generated in practice contains some unwanted light as defect light, several secondary rings and a central spot in the inner region of the main annular beam, which brings in noise signals. In order to study the defect light resources, we study the intensity distributions formed by conventional axicon pair and proposed system based on Fresnel diffraction theory. Then, an optimized optical path design method, named Filter Annular Beam Generation Optical Design (FABGOD), is proposed to eliminate the unwanted light to generate better quality annular beam. The design is based on the typical axicon-telescope, but it eliminates the inner unwanted light. The experimental results show that the beam regulation by FABGOD performs well. In addition, the alignment errors during the optical path build-up are discussed. The present work is a complementary research on hollow annular beam generation based on axicon-telescope, which takes the actual form of the both axicons into account to optimize the optical path, and also provides a new approach to generate annular beams with better quality in an economic way.