Neutral Beam Attenuation in Laser Ablated Atoms and Plasma.

Neutral hydrogen beam injection experiments have been performed to study the expansion of laser ablated carbon comprised of plasma and neutral atoms. Ablation of a planar graphite surface is achieved with a Q-switched ruby laser focussed to an intensity on the order of 10 ^{10} W/cm^2 . Independent measurements of expansion parameters have been obtained from temporally resolved optical spectra, Faraday cup measurements on the ablated plasma, and measurements of HeNe laser deflection from ablated carbon atoms and plasma. Peak line densities along chords 1-3 cm from the graphite surface have been obtained with neutral beam attenuation measurements using Rutherford scattering cross sections. Resulting line density peaks range from 2 times 10^{16} cm^ {-2} to 2 times 10^{15} cm^ {-2} for ablated carbon atoms and from 4 times 10^{14 } cm^{-2} to 3 times 10^{13 } cm^{-2} for ablated carbon ions, respectively. Experimental results are in excellent agreement with predictions based on a self-similar ablation expansion model.