Ultrafast Laser Machining of Dielectrics

High temperature pressure sensing is desirable for a broad range of applications related to re-entry of space vehicles and control of combustion processes; however, limited materials can sustain temperatures above 1000C while under time-varying pressure. A sapphire based optical pressure transducer has been proposed for measuring pressure at temperatures approaching 1600C. Manufacturing such sensors has focused on picosecond laser machining. Current research has produced models which can predict ablation depth for longer (ns) pulses and shorter (fs) pulses but there is an underwhelming amount of research focusing on predicting and understanding the mechanics of picosecond pulses. This is partially because of transitions in the mode of ablation processes associated with photothermal versus photochemical behavior. We put forth a general model for laser ablation using Maxwell's equations and a sharp interface equation and compare different constitutive laws which couple the two equations together. The proposed modeling results are compared to laser machining experimental data on sapphire from the literature to illustrate key material parameter uncertainty and sensitivity to the laser machining process. Bayesian uncertainty quantification is used to help validate the approximations within the constitutive equations.