Incubation effect during laser micromachining of GaN films with femtosecond pulses

We studied the evolution of the incubation effect during fs-laser micromachining of gallium nitride films with the number of laser pulses applied per sample surface area. The damage threshold fluence was measured using the zero-damage method and reduced from (0.61 ± 0.01) J/cm2 to (0.05 ± 0.03) J/cm2 when increasing the number of applied laser pulses from single-shot excitation to 105 pulses per spot, respectively. By applying the exponential defect accumulation model to the experimental incubation data, we determined a small value for the incubation parameter of (0.011 ± 0.001), indicating that gallium nitride has slow incubation dynamics. This information is important to achieve the desired control and high efficiency of fs-laser processing of gallium-nitride-based samples.