Pulsed-laser ablation of polytetrafluoroethylene (PTFE) at various wavelengths

The ablation rate of sintered polytetrafluoroethylene ( PTFE) targets has been investigated as a function of wavelength within the range 193 less than or equal to lambda less than or equal to 1064 nm and pulse durations 5 less than or equal to tau(l) less than or equal to 25 ns by means of various different lasers. In this parameter range, the apparent optical properties of targets and the depth of energy deposition are determined mainly by the scattering of the laser light. Therefore, measurements of the scattered light were performed for samples of various thicknesses by means of a modified UV-VIS spectrometer. For selected wavelengths, the angular distribution of the reflected and transmitted light intensity was determined. From these measurements, the coefficients for linear absorption, linear scattering and the scattering anisotropy were calculated using the inverse adding doubling algorithm. The results were tested by Monte Carlo simulation. With these coefficients the apparent optical penetration depths were estimated. These are about one order of magnitude larger than the ablation depths per pulse, which were determined from the weight loss of the targets.