Single-femtosecond-laser-pulse interaction with mica

Ultrafast, femtosecond laser pulse interaction with dielectric materials has shown them to have significantly higher laser fluence threshold requirements, as compared to metals and semiconductors, for laser material modification such as laser ablation. The interaction between femtosecond laser pulses and a dielectric, at a wavelength with negligible linear absorption, has usually been found to be weak, and multiple pulse irradiation is therefore typically used to observe quantifiable effects. In this study, the dielectric is the crystalline layered natural mineral muscovite, a mica with formula KAl₂(Si₃Al) O₁₀(OH)₂. A single ~150 fs laser pulse, ~800 nm wavelength, ~6 µm spotsize, is found to lead to a systematic range of laser modification topologies, as a function of fluence of the single laser pulse, including bulk removal. The fs laser pulse/material interaction is greater than expected for a standard dielectric at a given fluence. Optical surface profiling and FESEM are used to characterise the topologies. Contrasting the results of the two techniques supports the use of optical surface profiling to characterise the material modification despite its limitations in lateral resolution as compared to FESEM. The interlayer mineral water content of natural muscovite is proposed as the primary reason that mica behaves differently to a standard dielectric.