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<) into one repetition unit of the main polymer chain results in a well-defined decomposition pathway. The exothermic decomposition mechanism yields high energetic, gaseous products, which are not contaminating the polymer surface. The products of laser ablation were studied with time-of-flight mass spectroscopy (TOF-MS). All products are totally compatible with a photochemical decomposition mechanism and their high energies can be explained by a laser induced microexplosion. Time resolved techniques, such as transmission, reflectivity or surface interferometry, revealed a 'dynamic' behavior. Ns-interferometry showed that etching of the polymer nearly starts and ends with the laser pulse. During the initial stages of the irradiation, darkening of the surface was detected, which corresponds to a decrease of reflectivity and an increase of transmission. This is due to a decrease of the refractive index and absorption coefficient, caused by the photodecompostion of the polymer starting with the irradiation pulse.