Measurements of charged particles in the laser ablation plume of polymers

Charged particles in organic polymer plumes photoablated by ultraviolet lasers are measured with a Faraday cup assembly. In spite of a relatively low F₂ laser (157 nm) fluence <1 J/cm², relative charged fragment concentrations measured for polyimide, polytetrafluoroethylene, and polyethyleneterephthalate targets are ≳10^-3. Charged particle concentrations in the ablation plumes generated by an F₂ laser with polyethyleneterephthalate and polyimide targets are always higher than those in KrF laser (248 nm) ablation plumes at the same specific laser energy deposited on the target. Charged fragments have also higher velocities in the F ₂ laser ablation plumes. An exponential increase in the charged fragment concentration with increasing laser fluence suggests that the ions are mainly produced through electron-neutral collisions in the hot material core close to the target surface.