Non-diffraction-length, tunable, Bessel-like beams generation by spatially shaping a femtosecond laser beam for high-aspect-ratio micro-hole drilling

Bessel beams are advantageous in high aspect-ratio microhole drilling because of their immunity to diffraction. However, conventional methods of generating Bessel beams result in poor adjustability of the nondiffraction length. In this study, we theoretically describe and experimentally demonstrate the generation of Bessel-like beams (BLBs) with an adjustable nondiffraction length by using a phase-only spatial light modulator. In this method, nondiffraction lengths varying from 10 to 35 mm can be achieved by changing the designed phase profile (curvature). High-quality, high aspect ratio (560:1) and length-adjustable microholes can be drilled by spatially shaping a femtosecond laser beam.