Observation of two-photon excitation-induced fluorescence of ground-state neutral carbon atoms in vacuum generated by laser ablation of graphite

We demonstrated a practical gas production method for the ground-state carbon atoms in vacuum by pulsed laser ablation of graphite. The observation of 3P -3D two-photon excitation-induced fluorescence at 165.7 nm in the absence of a visible ablation plume proved the production of ground-state carbon atoms and enabled the evaluation of the velocity distribution and atomic density of the produced gas. With a low ablation fluence of 0.18 J/cm2 at 266 nm, the number of atoms produced was 1.5 x 108 per pulse. The temperature of the gas was approximately 5600 K. Spectral measurements of the plumes at higher excitation fluences of 8, 25, and 50 J/cm2 indicated that thermal sublimation at a low excitation fluence was essential to produce ground-state carbon atom gases. This method provides a promising source of atomic gas of carbon for laser cooling and precision spectroscopy when combined with precooling, such as using buffer-gas cooling.