Nanosecond laser ablation of graphite: A thermal model based simulation

Results on nanosecond pulsed laser irradiation and ablation of graphite are presented. Theoretical simulation based on a thermal model describing heat-transport and vaporization from a graphite target has been employed to calculate mass ablation rate per laser pulse. Attenuation of the incident laser beam in the generated vapor plume has been incorporated in terms of two coefficients, a and b, that serve as the only fitting parameters for our simulation model. Comparison between experimentally measured data and calculated mass ablation rate per pulse confirmed that the laser ablation mechanism was largely normal vaporization, in the incident laser fluence range of 10–25 J/cm2. Calculated maximum temperature reached by graphite target surface on laser irradiation and its dependence on average laser fluence enabled us to assess the possibility of the onset of explosive boiling in the target. A good agreement between model calculations and experimental results on the ablation rate for laser fluence below ∼30 J/cm2 validates our theoretical model. Our study facilitates a proper selection of laser fluence successfully minimizing laser induced explosive boiling in graphite targets, thereby ensuring deposition of pulsed laser ablation based carbon films and coatings with good microstructural and mechanical properties.