Experimental and numerical study of mechanism of glass modification process by continuous-wave laser backside irradiation (CW-LBI)

The modification of transparent materials using a femtosecond laser has been studied. We previously proposed a new method of modifying glass using a continuous-wave laser, named continuous-wave laser backside irradiation (CW-LBI), in which CW laser illumination induces a change in the refractive index without cracking the glass. In this study, we investigated the process of glass modification by CW-LBI using time-lapsed imaging and by calculation of the temperature. First, the modification of glass was observed by the shadowgraph method, and it was found that thermal radiation was included in the phenomena that occurred when the glass was modified. Second, the time-lapsed temperature distribution was calculated. The temperature distribution was roughly in accordance with the shape of the modified area observed in the shadowgraphs. We concluded that the radius of the modified area is dependent on the temperature reached in the glass.