Sub-nanosecond probing of the ablation of polyimide (Kapton) by ultraviolet laser pulses

Abstract

Ablation and etching of the surface of a free-standing film of polyimide (Kapton) by UV (193 or 248 nm) laser pulses (FWHM 20 ns) has been probed by pulses of visible laser radiation (596 nm; < 1 ns FWHM). The results were recorded photographically. The blast wave rising from the polymer surface on exposure to a single laser pulse in air was photographed in profile by back-lighting with the probe pulse. The earliest indication of the blast wave was seen just at the end of the UV pulse and was photographed at time intervals up to 2000 ns. The velocities of the blast wave at various fluences of the laser pulse at 193 and 248 nm were measured. These velocities were of the same order (105 cms-1) but somewhat smaller than the values reported by others from measurements made in a vacuum. A yellow emission could be seen at a distance of up to about 1 mm from the polymer surface.