PICOSECOND COHERENT RAMAN-STUDY OF SOLID-STATE CHEMICAL-REACTIONS DURING LASER POLYMER ABLATION

Multiplex picosecond time-resolved coherent anti-Stokes Raman spectros copy (CARS) is used to study the dynamics of a thin film of a polymer, poly-methyl methacrylate (PMMA), undergoing photothermal laser ablati on. Time-dependent CARS spectra of a PMMA Raman transition near 810 cm (-1) reveal line broadening, attributed to temperature increase, peak shift, attributed to rapid volume expansion, and the appearance of a n ew peak attributed to the formation of methyl methacrylate by picoseco nd time scale polymer thermal decomposition. This is believed to be th e first direct observation of a chemical reaction product in the solid itself, during laser ablation.