UV laser ablation of halonaphthalene doped PMMA: chemical modifications above versus below the ablation threshold

Laser-induced fluorescence is employed to monitor the photochemical modific ations that bromo- and iodon- aphthalene incorporated in PMMA films undergo following ablation at 248 nm. Following irradiation at low fluences with n anosecond pulses, photolysis of the dopants is found to result in the forma tion of naphthalene-like photoproducts, whereas above the threshold additio nal products are observed. Based on concentration studies, these are tentat ively ascribed to species containing two naphthyl groups. In close correspo ndence to the formation of the new species, the photolysis yields for both dopants are found to increase sharply above the threshold. Finally, the nat ure and extent of these photochemical effects is indicated to depend sensit ively on the laser pulse width. The mechanistic implications of these resul ts are discussed.