Ultrasonic machining, lapping and polishing of neodymium doped yttrium aluminum garnet laser crystal rod

Abstract

Fabrication of perfect laser crystal rod is a very challenging work where high shape accuracy and flawless surface are expected. Besides, most improvements in the processes or understanding of the physical process involved in fabrication of laser crystal rod are closely guarded as proprietary information, and specific details can be hardly found in technical journals and other literatures. The main purposes of the study are to investigate the potential of rotary ultrasonic machining (RUM) process to core drill Neodymium Doped Yttrium Aluminum Garnet (Nd:YAG) laser crystal material, and to study the effect of lapping and polishing parameters on the surface finish of the machined end faces of Nd:YAG laser rods. The effect of RUM machining parameters (spindle speed and feedrate) on surface integrity (surface roughness and opaqueness) and defects (ring marks, edge chipping size and chipping thickness) are studied. The feasible parameters to obtain the best surface roughness, opaqueness, straightness and diameter for Nd:YAG laser rod is 3000 rpm spindle speed and 5.4 mm/min, which is at low spindle speed and high feed rate. Nd:YAG crystal reaches the saturation point at fine surface finish of 0.124 micron at rotational speed of 60 rpm at 11 minutes of lapping time. Whilst for polishing process, Nd:YAG laser crystal reaches the saturation point with mirror-like and flawless surface finish of 5 nm at 23 minutes of polishing time. It is concluded that the RUM process exhibits a great potential method in producing laser crystal rods with better controlled machining condition. Meanwhile, LP50 lapping and polishing machine and its equipment is adequate to produce very fine surface finish of less than 10 nm on hard and brittle materials.