Direct measurement of polymer temperature during laser ablation using a molecular thermometer

Photothermal laser ablation is studied using poly-(methyl methacrylate) films doped with a dye, IR-165, which functions as a molecular heater and thermometer. Direct optical measurements of temperature are performed on samples heated by 100 ns near-IR pulses at 1.064 μm, at rates dT/ dt≊5×10⁹ deg/s. Below ablation threshold, the heat capacity measured by optical calorimetry is precisely the value obtained by conventional calorimetry. At ablation threshold, the peak surface temperature is T _abl=600°C. The increase in heat capacity observed above threshold, together with the results of a conventional thermal analysis, is used to determine the weight fraction of material decomposed at ablation time χ_th=0.02. With increasing pulse energy, the fraction decomposed increases and a more forceful ablation is observed, but the surface temperature does not continue to increase past T_lim=715°C, which is determined to be the limiting temperature for thermal decomposition.