Numerical simulations of thermal lens effect in K9 glass induced by millisecond laser irradiation

摘要

Non-uniform temperature field in optical transparent glasses induced by high power Gaussian laser irradiation wouldintroduce temperature gradient which will cause thermal lens effects inside materials. Such thermal lens influences onlong pulse laser processing are usually omitted in previous studies. However, thermally-induced refractive index changein situ could have a relatively large impact on subsequent incident laser especially under the action of high power laser.In order to obtain a quantitatively transient results of thermal lens effects caused by long pulse laser, we carried outnumerical simulations of temperature rise, refractive index change and their influences on light trail in K9 glass heatedby a millisecond pulse laser. Different laser energy and glass thickness were applied to reveal the dependence of thermallens and laser and glass parameters. Results show that the thermal lens effects would increase refractive index in K9glass and reconverge subsequent laser beam consequently whose amplitude is proportional to incident laser power andglass thickness. The simulation results are compared with the previous experimental results and are consistent inmagnitude of refractive index change. But there is a certain gap in refractive index field distribution in the direction oflaser radius due to the neglect of influence of refractive index raise to susequent lasers in temperature simulations. Thiswork would provide a reference in the field of millisecond pulse laser processing optical transparent materials.