Infrared femtosecond laser ablation of graphite in high vacuum probed by optical emission spectroscopy

We report infrared, ultra-short (780 nm, 120 fs) laser ablation of graphite in high vacuum. The plume characteristics are analyzed by wavelength-, time-, and spatially resolved optical emission spectroscopy. A multi-component structure of the plume is observed as a function of time, space, and laser fluence: (i) line emission from electronically excited carbon neutrals and ions; (ii) luminescence from excited C-3 radicals; (iii) broadband visible radiation, ascribed to black-body-like emission from larger carbon clusters. The analysis of the graphite plume optical emission indicates the existence of two different ablation regimes, with the emission of large graphite fragments at low fluences and carbon radicals and atoms at larger fluences, in agreement with the theoretical description of ultra-fast ablation of graphite.