Ryoichi KUWANO^*, Toshihiko KOGA, Tsuyoshi TOKUNAGA¹, Toshitaka WAKAYAMA², Yukitoshi OTANI³, and Nobuyuki FUJII

Department of Mechanical Systems Engineering, Polytechnic University, Sagamihara 252-5196, Japan ¹Department of Mechanical Science and Engineering, Chiba Institute of Technology, Narashino, Chiba 275-0016, Japan ²School of Biomedical Engineering, Saitama Medical University, Hidaka, Saitama 350-1241, Japan ³Center for Optical Research and Education (CORE), Utsunomiya University, Utsunomiya 321-8585, Japan

(Received September 5, 2011; Accepted January 19, 2012)

In this study, a method for generating ring intensity distribution at a refraction-type lens with an aspheric element was proposed, and the beam shaping optical element was finished using only ultra-precision cutting. The shape of the optical element and its irradiance pattern were determined from numerical calculation based on its geometrical and physical optics. An ultra-precision lathe was employed to fabricate beam shaping optical elements, and acrylic resin was used as the material. The transmittance of an optical element (a rotationally symmetrical body) with an aspheric surface fabricated using a single-crystal diamond tool was over 98%, and its surface roughness was 9.6 nm Ra. The method enabled the formation of a circular melting zone on a piece of stainless steel with a thickness of 300 μm through pulse YAG laser (λ = 1.06 μm) processing such that the average radius was 610 μm and the width was 100–200 μm. Circular processing using a ring beam shaping optical element can be realized by single-pulse beam irradiation without beam scanning.

Key words: beam shaping, aspheric lens, ring intensity distribution, YAG laser processing, ultra-precision cutting, single-crystal diamond tool

^*E-mail address: kuwano@uitec.ac.jp