Microfabrication and drilling using diffraction-free pulsed laser beam generated with axicon lens

Laser microfabrication using a diffraction-free beam (Bessel beam) was performed. Microfabrication with a deep focal depth is possible because a diffraction-free beam has a main lobe with a small diameter, which does not depend on propagation length. The diffraction-free beam was generated using an axicon lens, and the generation was confirmed using an optical microscopy image of a laser-fabricated spot on a silicon wafer. Nevertheless using a nanosecond pulsed Nd:YAG laser, microfabrication with a spot diameter < 1 μm was realized. As a result of the deep focal depth of the diffraction-free beam, even if we change the work distance within a range of several millimeters, we are still able to maintain the diameter of the laser- fabricated spots to approximately 1 μm. Since an almost straight penetration hole with a diameter of 3 μm was drilled into SUS304 foil (20 μm thick), it was found that the diffraction-free beam has a high feasibility for the high-aspect-ratio laser drilling of an opaque material due to its deep focal depth.