Solid state and liquid ablation of polyethylene-glycol 1000:: temperature dependence

Time-resolved investigations of solid and liquid phase ablation on the same sample (polyethylene-glycol (PEG) 1000) is presented in this paper. Because this polymer has a relatively low melting point (35 degrees C) we could study the ablation mechanism in both solid and liquid states of matter by varying the sample temperature in the 20-80 degrees C range. The target was irradiated by an ArF excimer laser (lambda = 193 nm, FWHM = 20 ns) at 1.95 J/cm(2) fluence. Pictures of the surface and the material ejection processes were taken by fast photography, with a temporal resolution of 1 ns using electronically delayed dye laser exposing pulses. It was demonstrated that plasma development and expansion (in the 0-50 ns time range), propagation parameters of shock waves and contact fronts did not depend on sample temperature in the investigated temperature range and state of matter. In contrast with this the significant material ejection (between 1-100 mu s) showed a strong temperature dependence. Below the melting point (solid samples) material ejection took place in the form of dense material clouds, and in the form of squish for liquid (molten) samples. The velocity of the ejected jets depended significantly on the temperature of the molten polymer sample. This might be due to the different viscosity of PEG 1000 in the investigated temperature range. (C) 2000 Elsevier Science B.V. All rights reserved.