Abstract: Blue light (360 nm ~ 500 nm) emission from the glass/liquid interface was observed during the
etching using a green (λ = 532 nm) nanosecond Q-switched laser. An organic dye, Oil-Red-O, dissolved in p-xylene was used for laser induced backside wet etching of borosilicate glass using the
visible light laser (visible-LIBWE). The blue light emission was confirmed to accompany the etching process. The UV-visible spectrum consists of characteristic peaks of metals, which are the components of the glass material. The maximal emission intensity occurs when the laser focusing is at
the glass/liquid interface. The threshold of the LIBWE etching is comparable to that of the occurrence of the blue light emission. We concluded that the emission is the plasma emission of the
etched glass. By measuring the plasma emission, the occurrence of the etching and the crack formation in the glass can be monitored in real-time.