Higher-order Bessel-like beams for optimized ultrafast processing of transparent materials

The controlled energy deposition by nonlinear absorption of ultrashort laser pulses offers a variety of different processing strategies for the machining of wide-bandgap materials. Considering laser-glass cutting applications, efficient single pass processes with volume modifications along the entire substrate thickness become possible using adapted focal field distributions [1]. The required extreme aspect ratios of longitudinal (given by glass thickness) to transverse (diffraction limit) beam dimensions are met by the class of Bessel-like beams that can be generated efficiently using phase-only spatial light modulators (SLMs) [2]. Simple multiplexing π-phase jumps or phase vortices ∝ exp (iℓθ) into the Fresnel-axicon-type phase mask [cf. Fig. 1(a)] enables to generate Bessel-like beams exhibiting ring- and petal-like transverse intensity distributions, respectively, while keeping the non- diffracting and self-healing beam properties [3]. By using pump-probe microscopy we proof that the resulting absorption distribution and, thus, the spatial energy deposition inside the material follows accurately the beam's simulated intensity profile.