Velocity distribution of neutral particles ejected from biological material under ultra short laser radiation

Neutral particles ejected from biological material under ultra short laser ablation have been investigated by laser post-ionization time-of-flight mass spectrometry. It could be shown, that beside ionized species, a substantial amount of neutral particles is ejected. A temporal study of the ablation plume is carried out by recording neutral particle time-of- flight mass spectra as a function of delay time between the ablation and post-ionization pulse. Close the ablation threshold, the mechanism of ejection is found to be of predominantely mechanical nature, driven by the relaxation of the laser-induced pressure. In this regime of stress con?nement, the ejection results in very broad velocity distributions and extremely low velocities.