Characteristic of ZnSe aspheric beam homogenizer for CO2 laser

Abstract

Laser processing is now being used increasingly in the area of electronics, especially, for drilling micro holes in printed circuit. But the intensity distribution of laser beam mainly based on Gaussian is not uniform. Therefore, the demand for uniform intensity distribution is rising rapidly in the field of heat processing. To obtain higher uniformity, attempts must be made to convert non-uniform Gaussian distribution into top-hat shaped uniform intensity distribution for smoothly bending laser beams. In this study the authors propose an aspheric beam homogenizer made from ZnSe that can convert non-uniform Gaussian distribution into top-hat shaped uniform intensity distribution. The ZnSe beam homogenizer consists of two aspheric lenses. First one converts Gaussian profile to uniform irradiation, and second one performs phase matching. The authors design this optical component with a special method based on wave optics. In the design, the authors define the target intensity distribution as the super-Gaussian shaped one instead of completely uniform top-hat shaped one. Compared with the homogenizers of traditional design, the newly designed homogenizer achieved 70% increase in the uniformity of signal intensity even after propagation. The paper reports the measured intensity distribution after propagation from the beam homogenizer with high power CO2 laser.