The effect of annealing on the subpicosecond breakdown behavior of hafnia films

Abstract

Subpicosecond laser induced breakdown of dielectric films has gained a great deal of attention in laser nano- and micromachining and in the development of optical coatings for the next generation of high-power ultrafast laser system. The understanding of the fundamental processes affecting the breakdown behavior and how they depend on the material properties and the film deposition is highly desirable for improving the coating performance. In the present work we compare the single and multiple pulse damage behavior of as-grown and annealed HfO₂ films. Annealing can reduce the film absorption near the band edge but its impact on the single and multiple femtosecond pulse damage behavior remained open. Damage measurements with pairs of pulses of variable subpicosecond delay in bulk fused silica revealed a partial recovery toward single pulse behavior on a few hundred fs time scale. We investigate if such behavior also occurs in hafnia films and identify the time scale for a full recovery. Our experimental results are compared with existing theoretical models[1], which allows us to suggest microscopic changes that occur during the annealing process.