Optical emission spectroscopy of carbon laser plasma ion source

Carbon laser plasma generated by an Nd:YAG laser (wavelength 1064 nm, pulse width 7 ns, fluence 4-52 J cm−2) is studied by optical emission spectroscopy and ion time-of-flight. Up to C4+ ions are detected with the ion flux strongly dependent on the laser fluence. The increase in ion charge with the laser fluence is accompanied by observation of multicharged ion lines in the optical spectra. The time-integrated electron temperature Te is calculated from the Boltzmann plot using the C II lines at 392.0, 426.7, and 588.9 nm. Te is found to increase from ∼0.83 eV for a laser fluence of 22 J cm−2 to ∼0.90 eV for 40 J cm−2. The electron density ne is obtained from the Stark broadened profiles of the C II line at 392 nm and is found to increase from ∼2.1×1017cm−3 for 4 J cm−2 to ∼3.5×1017cm−3 for 40 J cm−2. Applying an external electric field parallel to the expanding plume shows no effect on the line emission intensities. Deconvolution of ion time-of-flight signal with a shifted Maxwell-Boltzmann distribution for each charge state results in an ion temperature Ti∼4.7 and ∼6.0 eV for 20 and 36 J cm−2, respectively.