Study On Nanosecond/picosecond Laser High-precision Machining Of Quartz Glass

Quartz glass as a typical nonmetallic material has been applied in the aerospace, defense, scientific research and many other fields because of its excellent physical and chemical properties. However, high-precision processing of quartz glass is always a challenge due to the hardness and brittle properties of the material. Especiallly, it is always eager to achieve the micro/nano precision machining of micro holes and hole array on the quartz glass by breaking through some bottleneck problem. There great application demands for the micro-hole array of quartz glass in the microelectronics, MEMS device packaging, biological and medical fields. In this study, the high-precision machining of quartz glass by nanosecond/picosecond laser was researched in detail. A novel method based on laser processive-broadening path cutting(LPBPC) was presented for the micro through-hole machining. The calculation method of the parameters for LPBPC in the actual processing was given. At last, high-precision machining of the quartz glass shaped in circle hole, square hole and microwell array were achieved.According to the absorption characteristics of the green wavelength to quartz glass, nanosecond(ns) green laser has more advantages as a tool for processing of hardness and brittle glass than 10.6 μm CO2 laser and 1064 nm YAG laser which are the two common lasers applied in the field. The parameters of the nanosecond laser machining of the quartz glass, including laser fluence, defocusing amount, scanning times and scanning velocity, are systematically investigated by controlling variables during the experiments. The ablation threshold of quartz glass by nanosecond green laser is concluded to be around 7.97 J/cm2. The through-hole machining of 0.5 mm thick quartz glass is achieved with the method of layer by layer LPBPC. The through-hole with high quality crack-free edge has the diameter of 1 mm. The influence on the machining quality resulting from different environment(hot water, cold water and compressed air) and different machining starting surface of the workpieces are investigated. The experimental results show the warm water and cold water environmental conditions have the same effect on the processing quality, and compressed air is helpful to reduce the damage around the machined edge. The better machined quality was achieved by cutting from the rear side of the workpiece.Picosecond laser is a new type laser which is being developed rapidly in recent years. It is able to achieve an approximate "cold" ablation effect of materials by the laser. In addition, there are other advantages about the laser, such as compact and good sealing, high shock resistance and low maintenance cost, which make it more suitable for application in industrial environment. The laser parameters including laser fluence, defocusing amount, scanning times and scanning velocity of the picosecond laser with different wavelength(1064 nm, 532 nm) are systematically investigated by controlling variable method. The ablation thresholds of quartz glass for 1064 nm and 532 nm pecosecond lasers are evaluated to be around 3.49 J/cm2 and 2.01 J/cm2, respectively. The parameters of the LPBPC method are determined by calculation combined with the basic experimental results. The high quality machining of the through-hole in circle and square shape are achieved in the quartz glass with different thickness from 0.3 mm to 2 mm. Furthermore, the fine circle micro-hole array was machined in 0.3 mm quartz glass, in which the diameter of each hole is 500 μm and the distance between each hole is only 30 μm. A triangle micro-through-hole array in which the side length of each triangle is 500 μm is also achieved through this method.In the study, the comparative research on the characteristics of picosecond laser machining of quartz glass with different wavelength were carried out. The mechanism of picosecond laser machining of brittle inorganic non-metallic materials was analysed. The exploration of the picosecond laser precision processing technology and related mechanisms would provide instructive information for the development of the industrial application of ultrashort pulse laser micro-machining of hard and brittle materials.