Investigation on HF based etching of the polished K9 glasses and its application in the subsurface damage

To characterize the subsurface mechanical damage (SSD) of the polished optics, the material remove rate of the polished K9 glasses based on HF acid etching was investigated. The etching of optics is assumed to be isotropic, a polished K9 sample with special designed pattern was tested to find out the constancy of etching rate versus time. As the etching rate was determined, the polished samples were progressively etched till the SSD disappeared visually. During etching, topographies of the surface revealed the evolution of the subsurface damages, and by recording and comparing topographies, we may get the distribution of the SSD at every depth. The thickness of etched material refers to the depth of SSD as the subsurface damages were totally exposed. Compared with the Magnetorheological finishing tamper polishing, this method of measuring SSD is low-cost and simple.