PHOTOPOLYMERS DESIGNED FOR LASER-ABLATION - PHOTOCHEMICAL ABLATION MECHANISM

We have designed photopolymers based on a photolabile chromophore with absorption properties tailored for a specific irradiation wavelength. The introduction of the two photolabile groups (-N=N-N drop) into one repetition unit of the main polymer chain results in a well-defined d ecomposition pathway. The exothermic decomposition mechanism yields hi gh energetic, gaseous products; which are not contaminating the polyme r surface. The products of laser ablation were studied with time-of-fl ight mass spectroscopy (TOF-MS). All products are totally compatible w ith a photochemical decomposition mechanism and their high energies ca n be explained by a laser induced microexplosion. Time resolved techni ques, such as transmission, reflectivity or surface interferometry, re vealed a 'dynamic' behavior. Ns-interferometry showed that etching of the polymer nearly starts and ends with the laser pulse. During the in itial stages of the irradiation, darkening of the surface was detected , which corresponds to a decrease of reflectivity and an increase of t ransmission. This is due to a decrease of the refractive index and abs orption coefficient, caused by the photodecompostion of the polymer st arting with the irradiation pulse. (C) 1998 Elsevier Science B.V.