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Question questions about optical modeling 

Keywords: unified optical modeling ground
Forum: Processes Involving Optical Photons
Date: 08 Sep, 2006
From: Aaron Maschinot <Aaron Maschinot>

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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1 Feedback: Re: questions about optical modeling   (Peter Gumplinger - 14 Sep, 2006)
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