Time and space resolved plasma species dynamics of a laser carbon plasma in low pressure neutral background gas

Thin film deposition using laser produced plasmas has become a well established technique. In particular, carbon and diamond like carbon (DLC) thin film deposition using graphite targets has been investigated, using different parameter regimes. In particular, it has been found that morphological properties of thin carbon films growth with pulsed laser deposition in a low pressure neutral gas background strongly depends on the gas pressure. To unveil some of the plasma properties that lead to a particular thin film morphology, we have studied the time and space resolved evolution of the laser produced carbon plasma in low pressure Argon background, at 6.8 J/cm
²
fluence. In order to better understand the correlations between gas pressure and carbon film properties we have studied in further detail the dynamics and composition of laser produced carbon plasmas. An Nd:YAG laser pulse, 370 mJ, 3.5 ns, at 1.06 µm, at different fluences, below 10 J/cm
²
, is used to produce a plasma from a solid graphite target, in different neutral background gases, Argon, Helium and Nitrogen, at pressures below 1.5 Torr. The spectral emission in the visible is recorded with 15 ns time resolution and ∼3 mm spatial resolution. 20 ns exposure time plasma imaging, filtered with 10 nm windows at characteristic carbon species emission wavelengths, is used to study the dynamics of the expanding plasma. Faraday cups are used to characterize the energy spectra of the laser plasma ions. The carbon plasma emission is found to evolve from that characteristic of single ionized carbon, to a more complex one, where C
2
and C
3
molecular bands dominate. Several plasma fronts, with eitherionic or molecular composition, are seen to detach from the laser target plasma. Ionization of the background gas ahead of the initial laser plasma front is observed. The temporal and spatial features of the molecular carbon species evolution are found to be dependent on the actual gas pressure. Based on our observations we will present a general characterization of the dynamics of a laser produced carbon plasma in different low pressure neutral background dases.