LASER ABLATION OF DOPED POLYMERS - TRANSIENT PHENOMENA AS THE ABLATION THRESHOLD IS APPROACHED

The photochemistry of PMMA films doped with 1,1,3,3-tetraphenylacetone (TPA) has been studied using 266-nm laser excitation at energy doses below and above the ablation threshold. One-, two-, and at least three-photon processes are shown to play a key role in the delivery of energy to the polymer. Transient phenomena involving the formation of ground- and excited-state reaction intermediates lead to instantaneous absorbances during the laser pulse that are very different from those recorded under low-intensity conditions. Surprisingly, the ablation threshold is reached in the polymer samples without any dramatic change in the nature or behavior of the reaction intermediates involved in the decomposition of TPA when compared to those observed in solution, ether than an increase in light scattering due to bubble formation and fragment ejection from the polymer surface. The comparison of photoprocesses in polymers with the same reactions in solution allows for a qualitative discussion of the possible mechanism underlying the ablation of doped polymers.