Polymer ablation by ultra-short pulsed lasers

In this paper, we study the ablation behaviour of polyetheretherketone (PEEK) polymer samples of 100 mu m thickness when irradiated with visible laser light of 445 nn wavelength and 200 fs pulse width at 82 MHz pulse repetition rate. Etch depths corresponding to a particular laser power were measured at room temperature in open air, by counting the number of pulses required to perforate the sample. The laser focal spot size has been measured to be 0.03 mm(2) and was kept constant during the experiment. The surface topology of the polymer samples was investigated by Atomic Force Microscopy in the continuous contact mode. The obtained Atomic Force Microscopy images revealed no mechanical damage in the inner ablation crater wall. Plots of the ablation rate as a function of the laser power, both in a linear and a logarithmic scale, show a large deviation from a straight line. These findings along with the high average power used suggest that Multiphoton Dissociation is the predominant mechanism responsible for ablation in this experiment.