Fused-silica focusing lens for deep UV laser processing

A simple four-element fused-silica lens is presented that has a focal length of 31.2 mm and a relative aperture of f/1 for use as a focusing lens for deep UV laser processing. The curvature of the lens is designed with a practical design method to match the curvature of existing optical tools. By applying an 8.5-mm beam diameter Nd:YAG laser at a wavelength of 266 nm through the lens, we can easily achieve the percussion drilled into samples of 25-microm-thick tantalum foil with a hole diameter of <6 microm. When the lens and/or the sample is tilted, the shape of the drilled hole is in agreement with the Gaussian beam spot simulation.