Subsurface damage (SSD) generated in lapping process directly influences service performances of optical elements

which must be entirely removed in the following polishing process

however

the rapid inspection of SSD is unresolved for it is covered under surface. For the purpose of rapid

accurate

and non-destructive measurement of SSD produced in lapping process

a theoretical model of relationship between SSD and surface roughness (SR) was established through investigating median and lateral crack system in brittle surface induced by sharp indenter

and contribution of elastic stress field to the median crack propagation was also considered in the loading cycle. SSD depth of lapped K9 glass was measured by magnetorheological finishing (MRF) spot technique

in order to verify the validity of the relationship model. Finally

influences of lapping parameters on SSD depth were investigated experimentally

then

an effective lapping procedure was proposed in order to improve the machining efficiency of optical elements. The results show that there exists monotone increasing non-linear correlation between SSD depth and SR in optical lapping process

power of the power function is 4/3. Moreover

the influence of granularity of abrasive grains on SSD depth is more significant than lapping plate hardness

and the influence of lapping pressure and lapping plate revolution velocity can be neglected.