AlumaGem for polishing calcium fluoride

As the demand for lower surface roughness precision optics increases for high tech applications, polishing solutions that can achieve low surface roughness are needed. Pureon is committed to developing advanced polishing solutions for the precision optics market. To that end, we have turned our attention to optimal processing of Calcium Fluoride (CaF₂). CaF₂ has a broad wavelength transparency that allows it to be used in both ultraviolet (UV) and infrared (IR) applications. This is especially important for applications that require both UV and IR transmission like spectroscopy and imaging systems.¹ Precise polishing is needed to achieve a certain surface quality that is necessary for the final application. CaF₂ has a low hardness (Mohs hardness: 4) and is a brittle material; properties that can lead to increased edge chipping and insufficient surface quality.² Precision optics are commonly polished with cerium oxide abrasive slurries due to its inherent ability to exhibit both chemical and mechanical activity.³ The efficacy of cerium oxide abrasive slurries in CaF₂ processing is limited due to residual cerium oxide that is surface bonded. This residue proves difficult to clean and results in increased absorption in the UV wavelengths.⁴ To achieve a high surface quality with efficient processing times, Pureon has developed the ULTRA-SOL^® AlumaGem platform that utilizes both precisely graded diamond and alumina abrasives dispersed and suspended in an optimized carrier fluid for the bulk and final polishing steps. AlumaGem is a flexible platform that can be built with a range of diamond types and sizes depending on an application’s need. An in-depth study will be presented using 3 μm and 0.25 μm AlumaGem to process CaF₂ from ground to final polish with various polishing pads.