Blue light emission from a glass/liquid interface for real-time monitoring of a laser-induced etching process

An organic dye, Oil-Red-O, dissolved in p-xylene was used for laser-induced backside wet etching using a visible laser (visible-LIBWE) for the first time. Blue light (360-500 nm) emission from the glass/liquid interface was observed during the etching of borosilicate glass using a nanosecond Q-switched green laser. The 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. The maximal emission intensity occurs when the laser focusing is at the glass/liquid interface. The etching threshold measured by observing the blue light emission is comparable to that determined by the traditional method. 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.