Laser cutting of transparent materials with a Bessel-like beam has become increasingly popular over the last decade. Typically, elongated beam focus is used for cleaving of the glass due to effect of microcraks formation and connections between them.  It is much more challenging or nearly impossible to induce microcracks in polymers using the same method. Materials such as PET or PC can be processed using mechanical methods or long-pulse lasers. However, due to photothermal degradation causing yellowing and carbonisation the edge quality is poor and HAZ is unacceptable. One of the possibilities is ablative processing with ultrashort pulses. The cutting speed in cold processing regime is low, especially for thick polymer sheets. On the other hand, increasing heat accumulation during femtosecond laser processing can overcome ablation rate saturation caused by v-groove formation. At some point, however, it causes similar undesirable effect as long-pulsed lasers. Therefore, there is a need to introduce other method faster than cutting by ultrashort pulse ablation and less invasive than long pulse lasers. 

The experiments were performed using Deep Cleave beam shaper (Holo/Or) generating 1.0 mm focus length and 1.8 um waist diameter. Samples were processed using Jasper 20 (Fluence) femtosecond fibre laser generating 250 fs – 20 ps pulses with up to 100 µJ ultrashort pulse energy at 1030 nm wavelength.

The main challenge in Bessel-like beam cutting of polymer is to obtain homogeneous longitudinal modifications that are close enough to weaken the material in such a way to provide easy breaking after laser scan. The appropriate parameters were found by adjustment of the pulse duration and selection of the number of pulses in a burst. The polymer separation was presented for PC, PMMA and PET material. The effective speed of cutting using a 20 W laser source for a 1 mm thick PC reaches up to 700 mm/s when using a 200 kHz repetition rate in a single laser beam pass. Thicker polymer sheets can be processed using multiple passes.