Damage Control of Ultra-Thin YAG Crystal in Nano-Machining Process

Abstract

Yttrium aluminum garnet (YAG) crystal is one of the most widely used laser crystals because of its excellent properties. Thin disk laser with ultra-thin YAG crystal as gain medium is widely used in micromachining, imaging, military, medical, scientific research, and so on. Ultra-thin crystals with nanometer precision surface quality are easily damaged in nano-machining process. From the fracture mechanics, the critical fracture stress of ultra-thin YAG crystal was analyzed. The model of ultra-thin YAG crystal in chemical mechanical polishing (CMP) process, one of important nano-machining technologies, was established, and the effect of sticking mode and pressure on the stress magnitude and distribution of crystal were investigated. It was confirmed that the damage phenomenon in CMP process can be effectively controlled by using the edge padding sticking method. The optimized process parameters are as follows: the pressure should be less than 65 kPa, the optimized size of the edge pad crystal for YAG crystal with 10 mm × 10 mm is 10 mm × 20 mm, and the right-angle damage limit of the edge padding crystal is 3 mm. Finally, the optimization results were experimentally verified and the high-efficiency and high-quality nano-machining of ultra-thin YAG crystal with surface roughness S a 2.85 nm and the thickness 0.175 mm was achieved.