Picosecond coherent Raman study of solid-state chemical reactions during laser polymer ablation

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Abstract
Multiplex picosecond time-resolved coherent anti-Stokes Raman spectroscopy (CARS) is used to study the dynamics of a thin film of a polymer, poly-methyl methacrylate (PMMA), undergoing photothermal laser ablation. 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 new peak attributed to the formation of methyl methacrylate by picosecond time scale polymer thermal decomposition. This is believed to be the first direct observation of a chemical reaction product in the solid itself, during laser ablation.