Sub-wavelength micromachining of silica glass by irradiation of infrared laser with Fresnel diffraction

We investigated a simple and productive micromachining method of silica glass by the ablation using a 10.6 μm TEA CO₂ laser with a spatial resolution down to sub-wavelength scale. Copper grid mask with square apertures of 20×20 μm was attached to the silica glass surface, and the silica glass was irradiated by the TEA CO₂ laser light through the mask. As a result, circular holes were formed on the silica glass surface at the center of the apertures due to the Fresnel diffraction effect, and a minimum diameter of the hole was less than 3 μm. The mechanism of the micromachining was discussed based on the electric field distribution of the CO₂ laser light under the mask, by a 3D full-wave electromagnetic field simulation.