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Question Infrared (thermal) photons and gaps in/between volumes 

Forum: Processes Involving Optical Photons
Date: 01 Mar, 2017
From: Michael H. Kelsey <Michael H. Kelsey>

I have been asked to implement a simple-minded thermal photon simulation using Geant4. We already have a fairly detailed experimental geometry, which we use for our backgrounds modelling. The idea is to leverage all of that structure, and let Geant4 propagate blackbody photons (temperatures from 300 K down to 30 mK) to see where we need to add covers over cracks, etc. We are NOT trying to get temperature gradients, or estimate heating in our cryostat stages. We just want to see where the photons can get through, and roughly at what rate.

The problem is that at these temperatures, the photon wavelengths can be comparable to the dimensions of our components and the gaps we are trying to study. Small gaps should look like solid material to these photons, and long narrow gaps should be sensitive to the polarization vector. There should be diffractive effects where the IR exiting from large enough gaps spreads out in a fan.

I am pretty sure these processes are not implemented in the Geant4 optical physics toolkit. However, I am wondering if any other users or developers have approached these issues in the past, and if so, whether there's code out there which we could "borrow," or at least be inspired by.

  -- Michael Kelsey

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