Response of natural muscovite to a single femtosecond laser pulse

摘要

Muscovite is a naturally occurring crystalline mineral, a mica, with a unique layered structure with planes of lowcleavage energy spaced by ~1.3 nm in the crystal structure. It is a dielectric insulator. Freshly cleaved muscovite surfacesare extremely flat, clean and used in many technical applications of the material. Previous laser ablation study of micausing ultraviolet, nanosecond duration pulses, led to a poor finish at the process sites (K. Rubahn et.al., J. Appl. Phys. 86(5),2847, 1999). Interest in laser processing of the material, other than CO_2 laser cutting of mica sheets, was subsequently, and notsurprisingly, curtailed. Here-in we report the morphologies of the laser processed site affected by a single, ~150 fs duration, 800nmwavelength, 6 micron spotsize laser pulse focussed on the surface of a mica substrate. A systematic sequence of the morphology as thefluence of the single pulse is increased is obtained. Optical surface profiling and field emission secondary electron microsocopy areused to characterise the site morphology. Time of flight secondary ion mass specroscopy has been used to map the redistribution ofkey elements at the process site. Muscovite emerges as a fascinating material in its response to a femtosecond laser pulse. Usefulmarking without creation of debris beyond the footprint of the laser spotsize is achieved at a flunece as low as 2.4 J/cm~2. There isevidence of plasticity and cavitation within the sequence of morphologies found.