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Question Inconsistency in optical photon tracking? 

Keywords: fresnel refraction, total internal reflection, optical boundary process
Forum: Processes Involving Optical Photons
Date: 24 Nov, 2006
From: Kay Ulbrich <Kay Ulbrich>

Hello,

I have a problem with optical tracking across the boundary between two dielectrics. For the time being, I describe it without source code.

I am using a class "RadiatorBlock", which inherits from G4LogicalVolume in order to encapsulate geometrical information. I initialize an object of RadiatorBlock, using a G4Box solid, material is Air. Then in the constructor I completely fill it with Plexiglass bars as radiators for Cerenkov light. The optical properties for the material are set accordingly and optical boundary effects are enabled in the physics list.

Then I place this logical volume in another one, which is an instance of another class "DetectorArm", inheriting from G4LogicalVolume, material Air. This logical volume is exacly as big as the RadiatorBlock.

When placing the DetectorArm volume in the World volume and generating Cerenkov light in the radiator, the optical tracks are not as expected -- I always get "TotalInternalReflection" at the boundary of the volume, not Fresnel refraction, as expected. Additionally, the photons are not reflected back, but just refracted (180 more than reflection).

Anyway, when making the DetectorArm box only slightly larger (e.g., 1E-9*m in each direction) than the contained RadiatorBlock, everything works fine and I get Fresnel refraction.

On the other hand, when -- for test's sake -- I take a RadiatorBlock, then place it in a G4LogicalVolume of exactly the same size as this block and directly place this G4LogicalVolume in the World volume, I do not encounter this problem, although the number of logical volumes put one into another is the same.

Is there any related experience? I would not like to give up the concept of hierarchically stacking objects derived from G4LogicalVolume, because this makes the code easier to understand and maintain, even, if it introduces some additional logical volumes. Due to the reduction of the problem, the depicted case of course appears to be redundant.

Thank you for related information! Kay

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1 Feedback: Re: Inconsistency in optical photon tracking?   (Peter Gumplinger - 27 Nov, 2006)
(_ Feedback: Re: Inconsistency in optical photon tracking?   (Kay Ulbrich - 30 Nov, 2006)
(_ None: Re: Inconsistency in optical photon tracking?   (Peter Gumplinger - 30 Nov, 2006)
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