between the front and rear surfaces was negligible the absorptance was calculated from the temperature time variation as measured by a rear face thermocouple as shown the predicted behavior is matched by the measure the temperature initially rises rapidly then at a slower linear rate of 6670 k s until surface tension effects in the melt no longer resist the aerodynamic forces tending to remove the melt the temperature peaks at 2100 k when the removal process is established a steady temperature of approximately 1820 k exists until burnthrough occurs the present pyrometer is particularly suitable for measurements on bare aluminum because the absolute value for the emissivity of aluminum is very sensitive to surface conditions thereby making single wavelength pyrometry inappropriate fig1 shows two pyrometer signal time traces each for a bare aluminum 2024 alloy plate 0 4 mm thick irradiated at 130 mw m 2 one plate was in stagnant argon the other in stagnant air for the latter plate oxidation during irradiation increased the surface absorptance and thus the heating rate was faster than that for the plate in argon because melt was not removed in these examples t continued to rise well above the melting temperature until the laser was switched off the effect of latent heat on the heating and cooling rates is evident for such thin bare aluminum plates at incident intensities below 50 mw m 2 simple calculations see w w duley co 2 lasers effects amp applications academic new york 1976 chap 4 show that the temperature difference between the front and rear surfaces is very small in this case temperature obtained with the.