The characteristics of laser micro drilling using a Bessel beam

A Bessel beam is suitable for laser micro-fabrication because it possesses both a micron-sized focal spot and a deep focal depth. As the influence of focusing aberrations is much smaller than that of a convex lens, the generation of a Bessel beam using an axicon is very practical. In the case of laser micro drilling of austenitic stainless steel with a Bessel beam, suitable processing conditions were investigated. The threshold fluence to make a through hole increased with an increase in the sample thickness. For samples with the same thickness, the threshold fluence increased with an increase in the crossing angle. A small crossing angle Bessel beam can drill a deep hole with a small threshold fluence. A through hole with a diameter smaller than 10 μm can be made on a stainless steel sheet 20 μm thick by using a Bessel beam with a large crossing angle. The taper of the hole drilled with the Bessel beam is smaller than that with the focused beam from the convex lens.