Comparison of Au and Pt Foils for an Imaging Bolometer

Abstract

In the imaging bolometer a thin metal foil converts plasma radiated power to infrared radiation measured by an infrared camera. Calibration of the foil provides information on its sensitivity, which is helpful in selecting the best foil material. In this study thermal properties of submicron Au and Pt foils are investigated by heating the foils with a chopped HeNe laser beam (∼20 mW) and observing the temperature change, ΔT, and thermal time constant, τ, of the foil temperature. Assuming that the foil cooling is dominated by diffusion, we can compare the relative sensitivities of the foils by comparing the ratio of the thermal diffusivity to the thermal conductivity of the foil, κ/k, to the ratio ΔT/τ. The results indicate that Pt is more than 9 times more sensitive than Au even though standard thermal properties indicate that Au should be slightly (14%) more sensitive than Pt. This inconsistency indicates that the IR radiation is dominant over diffusion in the foil cooling. In that case the sensitivity should be evaluated by 1/k ∼ ΔT, which indicates that Pt is 8 times more sensitive than Au, while the ratio of thermal conductivities indicates that it should be only 4 times more sensitive.