Spectral measurements of incipient plasma temperature and electron number density during laser ablation of aluminum in air

Plasmas generated during incipient laser ablation of aluminum in air were studied using emission spectroscopy. A plasma emission model was developed, invoking one-dimensional radiative transfer, to describe the observed emission spectra, while taking into account the effects of continuum radiation. Theoretical spectra were calculated and compared to experimental spectra in the range 387-406 nm. Satisfactory agreement was found between the experimental and predicted spectra, especially at delay times of 30-200 ns, thus providing plasma temperatures and electron number densities as functions of delay time and laser irradiance (1.8-8.0 GW/cm(2)). In general, both the plasma temperature and electron number density rise at greater laser irradiances but drop at increasing delay times, with a more rapid drop for delay times less than 60 ns.