Energy deposition and incubation effects of nonlinear absorption of ultrashort laser pulses in dielectrics.

Although ultrashort laser has been widely employed in micromachining thanks to its excellent processing precision, one of the main challenges it faces when applied to 3D modification inside dielectrics is its processing efficiency. Many applications require multiple pulses to achieve significant modification to create structure such as microlenses. We report incubation experiments on energy deposition and the control of material modification in fused silica. This allows us to develop a practical incubation model by taking account different ionization mechanisms, in which coefficients relating to multiphoton and avalanche ionization change with laser shots due to accumulating defects. We then extend our study to the scheme where a pre-pulse is used to limit the absorption volume through pre-seeding. Both experiments and simulations show that the efficiency of laser processing can be significantly improved without sacrificing the spatial resolution with this method, especially for longer pulses.