Analysis of Transient Heating of Phosphor Coatings D. Greg Walker Department of Mechanical Engineering Vanderbilt University Nashville, TN. 37235 Stephen W. Allison Oak Ridge National Laboratory Oak Ridge, TN. 37831 Keywords: thermographic, phosphors, transient heating ABSTRACT This work examines how faithfully a layer of thermographic phosphor responds to a rapidly changing temperature of the substrate to which it is attached. A simple model is presented and applied to the specific situation of a ramp heating pulse of 200 ° C in 15 ms. The model predicts a time lag in temperature of about 6 ms for a 100 micron layer for a phosphor of thermal conductivity equivalent to glass. A 20 micron layer exhibits a 1/3 ms time lag. Experimental data for a rapidly heated nichrome wire provides supporting evidence that thin phosphor layers can follow such temperature changes on this time scale. INTRODUCTION Transient heating situations present a challenging class of problems for temperature diagnostics. A thin film thermocouple can respond quite well to rapid temperature fluctuations. But, this necessitates both contact and connection of the sensing element to the surface. Pyrometric methods can be used depending on the details of the test environment. High performance and expensive thermal cameras can generate temperature maps provided there is direct optical access to the test surface, there are no emissivity issues, and scattered or reflected light is not a problem. The present work examines the issue of coating thickness with respect to the use of thermographic phosphors for diagnosing rapid temperature changes. It is likely that transient thermal problems will increase as the use and development of micron and nanometer-level devices continues. One example is the heating of a piezoelectric microcantilever by rather moderate amounts of current 1 . A recent article surveys a wide range of techniques suitable for thermometry for nanotechnology. 2 Owing to the small sizes concerned, it is expected that temperature changes on this level can be rapid. Another example is transient heating associated with the rapid deposition of energy by a pulsed particle beam. Tests aimed at understanding stresses induced in proton-beam targets for neutron spallation showed temperature rises of about 10° C in a few