Study On Mechanism Of Polishing Sapphire With Short-Wavelength Laser

Sapphire crystal is a key component for optical glass and semiconductor substrate. It is wildly used in domains of science research and military affairs and so on. Sapphire is difficultly polished by mechanical or chemical way for its hardness and chemical stability. So laser polishing is the most likely way to polish sapphire for its noncontact removal.The author, based on the thermal reaction between laser and sapphire, established a suitable model of laser heating sapphire surface. The relation between parameters and ablation depth is given. Based on the photochemical reaction between laser and sapphire, the mechanism of material removal is studied. Surface character formed by laser drilling and laser polishing with different parameters such as laser pulse energy and scan speed was observed in SEM and optical microscope to analyze the mechanism of laser removal with the help of the model established formerly.It is concluded that:1. In 532nm-wavelength laser polishing of sapphire, thermal reaction mechanism is predominate while photochemical reaction mechanism created by multiphoton absorbtion is predominate in 355nm-wavelength laser polishing of sapphire.2. The damage threshold is at about 20mJ in 532nm-wavelength laser polishing and 0.5mJ in 355nm-wavelength laser polishing. The ablation depth is inceased dramatically at 40mJ in 532nm-wavelength laser polisih and at 0.5mJ in 355nm wavelength laser polishing.3. Experimental research result confirmed the theoretical research result.4. In 532nm wavelength laser polishing of sapphire with different laser energy, material is removed by fracture at 20mJ, 40mJ and is removed by melting at 60mJ. In 355nm wavelength laser polishing with different laser energy, material is removed by micro-fracture at 0.2mJ and is removed by both photochemical reaction and micro-fracture at 0.9mJ and is removed by photochemical reaction at 2mJ. 5. In 532nm wavelength laser polishing of sapphire with different scan speed, material is removed by fracture, both melting and fracture and melting at 1mm/s, 5mm/s, 10mm/s respectively. In 355nm wavelength laser polishing of sapphire with different scan speed, material is removed by both chemical reaction and micro-fracture at 0.2mm/s and is removed by micro-fracture at 0.6mm/s and 1mm/s..