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Feedback Re: surface with 98% reflection and 2% transmission of optical photons 

Keywords: optical photons reflectivity transmission surfaces
Forum: Processes Involving Optical Photons
Date: 27 Mar, 2008
From: Gumplinger Peter <Gumplinger Peter>

Hello Matthew,

Thanks for your posting. You are bringing up yet another type of possibility of what might happen at an optical interface.

Let me clear up one thing first. The property 'REFLECTIVITY' applies only to dielectric_metal surfaces (as you found out). It is ignored for dielectric_dielectric surfaces where the reflectivity is calculated from Fresnel's equations. On the other hand, again as you found out, for dielectric_metal surfaces where the REFLECTIVITY is decisively used, photons not reflected are absorbed. This, of course, is the case for most thick reflectors, considered only at the time the code was written. I appreciate that there may be situations where the photon may simply continue on through the interface and where the interface, although specified as 'dielectric_metal', may in fact be between two dielectrics. The user simply may want to specify a reflectivity based on numbers rather than Fresnel's equations.

I looked into the code and I believe a simple modification (if you have access to the G4 source) would allow you to do this; comment out the line:

http://www-geant4.kek.jp/lxr/source/processes/optical/src/G4OpBoundaryProcess.cc#L581

To summarize: (1) specify your surface as dielectric_metal, (2) specify the reflectivity as you have done and (3) comment out this line of code; plus, of course, make sure that the "metal" media across the interface has an index of refraction specified for it, or else photons will be stopped on account of finding themselves in a media without refractive index.

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1 None: Re: surface with 98% reflection and 2% transmission of optical photons   (Matthew - 08 Apr, 2008)
(_ Idea: Re: surface with 98% reflection and 2% transmission of optical photons   (Peter Gumplinger - 10 Apr, 2008)
(_ Feedback: Re: surface with 98% reflection and 2% transmission of optical photons   (Matthew - 14 Apr, 2008)
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