Performances of 800 nm femtosecond laser ablation on natural and synthetic quartz
Performances of 800 nm femtosecond laser ablation on natural and synthetic quartz (in EMPG XII Toulouse; Experimental mineralogy, petrology and geochemistry symposium, Jannick Ingrin (editor) and Mike Toplis (editor))
European Journal of Mineralogy (June 2011) 23 (3): 391-400
A commercial femtosecond laser system operating at its fundamental wavelength (lambda =800 nm, near Infra-Red) was used to ablate both synthetic and natural quartz on polished and unpolished surfaces. Ablation rates and maximum depths were determined using two distinct optical setups: a 25 mm focal length Cassegrain reflecting objective, and a 50 mm focal length convergent coated lens. All samples were ablated with the same laser beam at E (sub 0) =1 mJ, tau =60 fs, f=5 Hz and N=10-8000 shots. The depth of ablation craters obtained with the lens shows a linear increase with shot number N up to N=2000 shots. Then the depth increases much less with N and reaches a plateau above N=3000 shots. Maximum depth was close to 1300 mu m for N=3000 shots. Using the reflecting objective, ablation rate starts from 0.42 mu m/shot and decreases rapidly to 0.02 mu m/shot at a maximum depth of 350 mu m for N=1500 shots. Ablation thresholds (F (sub th) ) were calculated for 1 and 10 consecutive shots with energy increasing from E (sub 0) =0.1-2 mJ/pulse. Threshold values varies from F (sub th) =0.1 J.cm (super -2) (unpolished, 10 shots) to F (sub th) =2.9 J.cm (super -2) (polished, single shot). The energy penetration of IR-femtosecond laser pulses in quartz has been calculated at l=271 nm. The low absorption of IR wavelengths in quartz affects the ablation efficiency in the first shots. The associated non-linear effects are visible on a crater FIB foil observed with TEM as progressive high-pressure photomechanical damage developing under the ablation pit. The present study emphasizes the potential of IR-femtosecond laser for ablation of highly transparent material, and provides reliable data for LA-ICP-MS applications in earth sciences.