High-Quality Flat-Top Micromachining of Silica by a CW CO$_{2}$ Laser

This letter demonstrates a simple and fast technique that dramatically improves the micromachined surface quality of silica substrates processed by a continuous-wave CO$_{2}$ laser. When sufficient laser power is directed at the surface of a sample, its temperature increases beyond the boiling point. Melted material is ejected and a groove is created. Some of the ablated material redeposits on each side of the groove, altering the surface quality of the substrate. To circumvent this problem, we deposit a polymer overlay as a sacrificial film which protects the surface during the ablation process, resulting in a flat surface on either side of the groove at very high writing speeds. The grooves can be used as an aid to passive alignment for an optical fiber, as diffractive optical elements or to create high-quality microfluidic chips.