Laser-induced breakdown spectroscopy for analysis of chemically etched polytetrafluoroethylene

Laser-induced breakdown spectroscopy (LIBS) is used to analyze chemically etched polytetrafluoroethylene (PTFE). The elements O, F, H, and Na are determined qualitatively in the depth dimension. It is shown that O, H, and Na signals are greatest at the surface and decrease as the laser burrows through the etched layer into the bulk. In contrast, the fluorine signal is a minimum at the surface and increases with depth. The average ablation rate for PTFE under the experimental conditions is found to be 1.9 microm per pulse. Using this value, the depth of the etched layer is determined to be 8 microm. A calibration curve produced by analysis of different polymers gives mole fractions of O, F, and H at the surface of the etched PTFE of 0.2, 0.3, and 0.1, respectively.