Study On Short Wavelength Laser Polishing Of Sapphire

Sapphire (molecular formula is Al)2O₃) is one kind of multifunctional material. Ithas high rigidity and melting point, good light transmission and thermal conductivity,excellent electrical insulation, stable chemical performance. It belongs to ionic crystalof trigonal system as well and is typical difficult to cut hard brittle material. It is hardto obtain the ideal non-traumatic surface by using the classical method, and the polishing efficiency and yield is low. This paper introduces a new method of polishing sapphire—short wavelength laser polishing of sapphire against the irreformable surface quality problem during the polishing process. Green laser(λ=532nm) andultraviolet laser(λ=532nm) are used to polish sapphire. Based on the experimental analysis, theeffects of parameters of green laser and ultraviolet laser polishing of sapphire on surfaceroughness are studied in this paper.In order to find out the smallest energy density when the sapphire was just destroyed andselect the suitable energy density in polishing, we consider the effect of energy density on depth ofhole according to laser drilling experiment. The ablation threshold of green laser is 2.3J/cm²-3.1J/cm², and the ablation threshold of ultraviolet laser is 1.91J/cm². To find out the suitablescanning speed, we consider the relation of spot overlapping and scanning speed. To select thesuitable laser angle of incidence, we consider the actual experimental condition.The effects of parameters (pulse energy, scanning speed, angle of incidence and scanningway) on surface roughness have been studied during the green laser and ultraviolet laserexperiment. The main conclusions are obtained as following:1. Compared to green laser polishing of sapphire, ultraviolet laser polishing of sapphire canget lower surface roughness2. With the increasing of pulse energy, the surface roughness of sapphire increases at first, andthen decreases during green laser polishing. And when the pulse energy is 20mJ, we can get bettersurface roughness. With increasing of pulse energy, the surface roughness of sapphire decreasesduring ultraviolet laser polishing, and the suitable pulse energy is 1.5mJ.3. With increasing of scanning speed, the surface roughness of sapphire decreases at first, and then increases during green laser polishing. And when the pulse energy is 10mm/s, we can getbetter surface roughness. With increasing of scanning speed, the surface roughness of sapphireincreases during ultraviolet laser polishing, and the suitable scanning speed is 0.2mm/s.4. Green laser polishing and ultraviolet laser polishing come to the same conclusions: thebigger of the angle of incidence, the better of the surface roughness of sapphire.5. Green laser polishing and ultraviolet laser polishing come to the same conclusions:Compared to one time scanning, rotated sapphire and multiple scanning can obtain better surfaceroughness.