Second-Surface Mirror Effects in Thin-Film Absorber Layers
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The Thermal Radiation Group at Virginia Polytechnic Institute and State University has been developing analytical and numerical heat transfer models for NASA's Langley Research Center for more than 25 years. Recent versions of these models are being used in the design of the next-generation thermal radiation detectors intended for Earth radiation budget campaigns. The current investigation presents three models for the absorption of electromagnetic radiation in thin films. The first assumes a surface heating boundary condition. The second model, derived from electromagnetic theory, is an analytical volumetric heat generation model. This model can be applied to a semi-infinite medium or to a thin-film absorber layers behaving as a second-surface mirror; that is, a semi-transparent coating deposited on top of a reflective surface. The third model is a statistical volumetric heat generation model that is derived using the Monte Carlo ray-trace (MCRT) method. These models are compared by using them to predict the transient temperature response of a generic thermal radiation detector. Results are presented for absorber layers in which the index of refraction is equal to the extinction coefficient. It was found that both of the volumetric heat generation models produce identical results. It was also found that the response of the detector due to shorter wavelengths deviates less from the surface absorption model than at longer wavelengths. A second-surface mirror reflection model for the absorber layer of the thermal radiation detector is also presented in this thesis.
- Masters Theses