On the angular dependence of focused laser ablation by nanosecond pulses in solgel and polymer materials

Focused laser ablation by single laser pulses at varying angles of incidence is studied in two materials of interest: a solgel (Ormocer 4) and a polymer (SU8). For a range of angles (up to 70° from normal), and for low-energy (<20 μJ), 40 ns pulses at 266 nm wavelength, the ablation depth along the direction of the incident laser beam is found to be independent of the angle of incidence. This allows the crater profiles at oblique incidence to be generated directly from the crater profiles at normal incidence by a simple coordinate transformation. This result is of use in the development of simulation tools for direct-write laser ablation. A simple model based on the moving ablation front approach is shown to be consistent with the observed behavior.