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-mu-m, at rates dT/dt almost-equal-to 5 X 10(9) 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-degrees-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 chi(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-degrees-C, which is determined to be the limiting temperature for thermal decomposition.