Alumina abrasive grains mediated grinding induced glass surface and fractal analysis of SiO2 glass

Abstract

Fabrication of optical components such as passive optics (mirrors, prisms, lenses) or active optics (polarizer's, laser gainmedia, adaptive optics) starts froma bulkmaterial and reaches to the required size and shape.To achieve the required specification of the component, a series of process has to be followed fromgrinding to polishing stage. Initially, in grinding stage,material removal is faster,withmore surface damage and less geometric control.During polishing stage,material removal is slower,with no surface damage butwith greater geometric control.Hence, to achieve good surface quality, the component or work piece has to be controlled fromgrinding stage.We present an advanced surface and fractal analysis study on fused silica samples processed with different grit sizes such as 3, 5, 12, and 25μmaluminium oxide (Al2O3) abrasives. Themaximumsub surface damage (SSD) with respect to size of the abrasive grain ranged between 30μmto5μmin empiricalmodule. In theoreticalmodule it varied from45μmto 5.4μmfor fused silica glass,mediatedwith loose abrasive aluminiumoxide powder of 25μmand 3μm respectively.An experimental investigation is reported on the increasing effect ofAl2O3grit sizes on the surface topography such as average roughness (Ra),which varied from57 nmto 847 nmfor 3 μmand25 μmAl2O3abrasives respectively.Three-dimensional image analysis was captured through Phase Shift Interferometry (PSI) andCoherence Correlation Interferometer (CCI) technique. Field Emission Scanning ElectronMicroscope (FESEM) techniquewas utilized to characterize theAl2O3powders and the processed fused silica samples. Later, the images have been analysed using two-dimensional multifractal detrended fluctuation analysis (2D-MFDFA) to understand and confirmthemultiple fractal nature on fused silica samples caused by varying grit size ofAl2O3abrasives.