| Abstract [eng] |
Bessel-Gaussian beams are increasingly used in micro-processing of transparent media due to their unique properties of diffraction-free spreading space and extremely high focal length/width ratios, which are commonly used to speed up or improve existing processes, while the most common application is glass cutting with Bessel-Gaussian beams. But there are also more exotic variations with more complex transverse intensity distributions, potentially opening up even more applications in micromachining, like higher-order n vector or vortex Bessel-Gaussian fibers with a doughnut shaped transverse intensity distribution. Bessel-Gaussian beams of order n are already being used to obtain ring structures by two-photon polymerization or even to produce graphene micro and nano-disks. Auxiliary processes, such as selective chemical etching, are also often used for process development and improvement. The significant increase in the etching rate of the material in the laser-modified zones allows the formation of various micromechanical devices or forming long and narrow channels by etching arrays of holes. Thus, the combination of selective chemical etching and higher order n vector and vortex Bessel-Gaussian fibers with could become an excellent tool for improving micromachining processes, for example by making holes of a slightly larger diameter or perhaps for a faster and/or better quality result. The aim of this work is to efficiently realize high-quality higher-order vector Bessel-Gaussian beams and to investigate the applicability for efficient thorough hole fabrication using selective chemical etching. In this work, quality vector Bessel-Gaussian beams (n=1, n=4 and n=6) were efficiently realized with S-wave plates of an order of n (Workshop of Photonics) and an axicon which produces non-diffracting vector Bessel beams from the resulting beam. Polarizer is used if individual beam components are formed. Two optical systems for high-quality fiber generation have been tested: involving spatial filtering and diffractive axicon. In both cases the results were in close agreement with the results obtained from modeling beam propagation in such systems. The generated vector beams of the order n form tubular beam in space whose diameter depends on the order n. The individual perpendicular components separated by the polarizer are also ring structures, but consist of 2n intensity peaks. The measured intensity distributions were not ideal: the central ring intensity variations up to ~ 20 %. Tubular structures of ~ 3 μm (when n=1), ~ 7 μm (when n=4) and ~ 10 μm (when n=6) diameter in SCHOTT D263T glass sample were successfully written using generated beams. Quality of the structures were highly improved by multi-pulse laser exposure. Structures written with n=6 beam and separate component were chemical etched in 80 °C and 30 % concentration aquatic KOH for 60 h in an effort to obtain thorough holes and test different writing parameters. Maximum etching speed of 3.23 μm/h and selectivity of 4.07 were obtained by using 500000, 1 ps, 52.5 μJ energy pulses with separate polarization component of generated beam, when type II modifications (microcracks and micro-voids) were formed in the volume of the sample. |
