Model of the Effects of Femtosecond Laser Pulse Energy on the Effective Z-Position of the Resulting Cut after Laser-Induced Optical Breakdown

Presented in this study is a validated semiempirical model of the effects of femtosecond laser pulse energy on the effective z-position of the resulting cut after laser-induced optical breakdown. Different energy levels (for the same spot spacings, i.e., different doses) running from 1.07 x (similar to 60 nJ) to 3.8 x (similar to 215 nJ) of the laser-induced optical breakdown (LIOB) threshold (similar to 56 nJ) were used to perform flat cuts within flat poly(methyl methacrylate) (PMMA) samples at the same nominal focus position (depth within the material). The z-locations of the effective cut and the anterior surface of the PMMA were confocally determined. The difference (PMMA_surface-Cut_plane) was used as a surrogate for the effective shift in the z-position of the cut. A consistent and continuous shift towards less deep cuts was observed for increasing pulse energies. The z-shift spreads by up to 22 mu m thinner cuts for the largest pulse energy (3.8x LIOBTh, similar to 215 nJ). Higher pulse energies seem to significantly reduce the cutting depth. The results for PMMA are in good agreement with the moving LIOB model.