Thermal coupling and etch rate measurements are reported for polyethylene terephthalate and polyimide films irradiated at excimer laser wavelengths of 193, 248, and 308 nm. Thermal energy balance is observed up to a threshold fluence but above this the energy absorbed remains approximately constant, the excess energy being carried away by the ablated material. The ablated material appears to have a temperature >103 K as determined by calculations based on the thermal energy loading and relaxation time estimated from IR measurements. These results provided useful information on the interaction mechanism.
Spectroscopy and fast photography have been used to study the luminous plume produced by ablative etching of polyimide and polyethylene-terephthalate polymer films with the XeCl laser. The time dependence of the expansion for various environmental gas pressures has been studied in this way. The results show that at low pressures (<0.5 mb) the expansion approaches a free expansion into a vacuum, while at 15 mb the time dependence is close to that predicted by an ideal blast wave model. It is suggested that a significant fraction of the luminous species detected spectroscopically may be created in the shock front at the plume/environmental gas interface.
Stable, well-defined conical structures have been observed to develop on the surface of excimer laser etched polyimide. Deliberate seeding shows that these are induced by the shielding effect of particulate impurities and indicates means for controlling the surface microstructure.
Conical features produced on excimer laser ablated polymers are shown to provide a sensitive technique for determining ablation thresholds. This has been applied to polyimide, polyethylene terephthalate, polyethylene, and nylon 66 ablated using the 157 nm vacuum ultraviolet F2 laser.
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