Multi-focus Laser Processing System Development And Research On Separation Brittle Transparent Material

Brittle materials are widely applied in the field of aerospace，national defense andelectronics. Mechanical processing brittle materials, especially on optical crystals withimportant strategic status, cannot meet the application requirements of high quality andefficiency. Exploring new technology is imminent. Laser cutting technology has widelyused in brittle materials processing, but laser cutting with one focus is confined by thematerial thickness. Laser processing thick material is a problem which needs to beaddressed.In this dissertation, based on laser thermal stress cleaving technique, a newmulti-focus laser processing system was developed, which can reduce stress differencealong thickness, induce crack propagation and realize thicker material separation with highquality. Combined with the equipment conditions of our laboratory, the systemdevelopment scheme was discussed in detail. The multi-focus laser processing system wascomposed of continual wave laser, polarization splitting prism, quarter-wave plate, focuslens, sphere reflector with a hole, planar reflector and precision worktable, etc.The multi-focus derived system was calculated in detail by sequential mode. Then, theZEMAX optical design software was used to simulate the multi-focus laser processingsystem, adopting the method of combining sequential mode with non-sequential mode. Thedesign is verified by the multi-focus experiments through the air medium, and the errors ofmulti-focus position are less than2mm. The main contributing factors to the system wereanalyzed both from theoretical simulation and experimental test, which included the designof multi-focus derived system, material (include thickness and quality), surface parallelismand the position deviation of components, etc.The transmission characteristics of multi-focus laser focused into brittle materialswere studied, especially into birefringent crystal. The transmission characteristics of laserhave a lot to do with the angle between optical axis and incident laser. The adverse effect of e-ray focus distortion must be considered during laser processing.Experimental researches on multi-focus laser separation K9glass with thickness80mm and KDP crystal with thickness less than70mm were carried out. An initial crackwas prepared on the lateral surface of glass with laser. Under the laser processingparameters of maximum power23.6W and scanning speed100μm/s, the partly separatingsidewall is acquired without subsurface damage, and small surface roughness. Limbicdamage is also very small. In the research of separation KDP crystal, the quality of crystaldramatically influences the crack propagation with the interaction with multi-focus laser.KDP crystal with thickness40mm is successfully separated. But the quality of separatingsidewall is not very good, the process requires further study. The researches show that themulti-focus laser processing system separation thick brittle transparent material is feasibleand has vast application prospects.