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I have a couple of questions about optical modeling in GEANT4 for anyone who may know. I am trying to simulate optical photons passing through a series of contiguous blocks of materials with different optical properties. None of the blocks is coated with anything. 1) Optical properties are entered via arrays as a function of photon momentum over a range of momenta. But what happens when a photon with an energy not explicitly specified in the array is encountered? Does GEANT4 perform some sort of a spline in between listed optical values? What happens above (below) the highest (lowest) momentum in the array? 2) I have read through the UNIFIED paper as well as the optical modeling section of the User's Guide. I like the concept of the "sigma_alpha" variable to specify surface roughness in the UNIFIED model, and I would like to use this model (as opposed to GLISUR) in my simulation. However, I am confused as to why I need to specify the specularlobe, specularspike, backscatter, reflectivity, and efficiency arrays. In my simulation, I have no wrappings or coverings surrounding individual blocks. Instead, the blocks are directly contiguous. Am I correct in thinking that the above listed variables need to be specified only when thin coverings are used? In my simulation, my finish is "ground", not "groundfrontpainted" or "groundbackpainted". It seems to me (maybe incorrectly) that, in the absence of any thin coverings surrounding materials, the physics is completely determined once "sigma_alpha" is chosen. Thus, I do not see the need for these other variables. Thanks so much, Aaron
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