Study On Subsurface Damage Of Optical Glass After Lapping

The life, stability, imaging quality, coating quality and laser induced damage threshold of the opticalelement are directly affected by subsurface damage(SSD) caused by lapping. Therefore, the accuratemeasurement of SSD depth is the prerequisite to ensure the removal amount in the subsequent processingand make sure that the SSD is removed completely. An overview of the generation mechanism of SSD isintroduced. Differential chemical etching method(DCEM) and magnetorheological finishing spot method(MRFSM) are employed to measure the SSD depth of K9glass lapped by free and fixed abrasive. A quickand accurate measurement method of SSD depth is obtained by comparing with DCEM and MRFSM. Themain work and results in this paper are as following:1. DCEM was adopted to test the SSD depth of K9glass lapped by abrasives and fixed abrasive. Therelationship between the material removal rate, surface appearances, surface roughness of K9glass anddifferent lapping ways was studied. The relationship between the above and the different particle sizes wasanalyzed. The result shows that better machining quality can be obtained by lapping with fixed abrasivethan abrasives.2. MRFSM was employed to measure the SSD crack depth of K9glass lapped by abrasives and fixedabrasive. The relationship between crack depth, residual stress depth and the different particle sizes wasdiscussed. The results of MRFSM and DCEM were compared to obtain the residual stress depth of K9glass. The relationship between SSD crack, residual stress depth and the different particle size wasanalyzed. The result shows that higher measuring accuracy can be obtained by using MRFSM than DCEM.3. The SSD generation mechanism and mechanical characteristics of optical material were introduced.Models of abrasives and fixed abrasive lapping were established. The simulation results show that lowerSSD crack depth can be obtained by lapping with fixed abrasive than abrasives. And fixed abrasive lappingis suitable for precision/ultra-precision machining.Finally, the conclusions of this paper were summarized and the further work on the theory andtechnology of SSD measurement was prospected.