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Forum: Processes Involving Optical Photons
Date: 23 Feb, 2010
From: Paloma <Paloma>

Hi Peter,

I continue doing tests in geant4. And I have some new questions for you. Now

I'm checking the behaviour of an apd changing the features of the optical

surface between the crystal and the apd or the crystal and the out box. My

setup is a crystal(box 10x10x60) and an apd(box with dimensions 10x10x10). All

 of this is contained in a box, called mainBox. I have two optical surfaces: 

between the crystal and the apd and between the crystal and the mainBox. In all

the pictures sl means specular lobe, ss means specular spike and sa means

sigmaalpha. I have one million of optical photons going in random directions

from the (0,0,0)(this point is the center of the crystal)

The numbers in the X-axis means:
 0: Undefined
 1: Fresnel Refraction
 2: Fresnel Reflection
 3: Total Internal Reflection
 4: Lambertian Reflection
 5: Lobe Reflection
 6: Spike Reflection
 7: Backscattering
 8: Absorption
 9: Detection
 10: Not At Boundary
 11: Same Material
 12: Step To Small
 13: No Rindex
 14: Unknown

My questions are:

1)In the first attachment we have the process type for a groundbackpainted

 surface in the walls of the crystal, type dielectric_dielectric and the 

constants are specified in the picture. The properties of the crystal-apd

surface are fixed(dielectric_metal,polished and sigmaalpha equal to zero)

      http://hypernews.slac.stanford.edu/HyperNews/geant4/get/AUX/2010/02/23/07.51-46600-edAllDirIdentProcType.png

Why the number of optical photons detected is so low for sl=1,sa=10 compared with sl=1 and sa= 0.

2)In this figure we have the identification process type for a ground surface

but now the surface between the crystal and the mainBox is dielectric_metal and

ground.I think that is strange that the number of optical photon detected

change so much between sa=0 and sa=10 with sl=1.

      http://hypernews.slac.stanford.edu/HyperNews/geant4/get/AUX/2010/02/23/07.51-9419-undAllDirIdenProcType.png

3)In this attachment we have the process type for a ground surface in the walls

 of the crystal, type dielectric_dielectric and the constants are specified in 

the picture. Why the number of detections change so much for sl=1 and sa=10,

and ss=1 and sa=10 compared with the case with sa=0

      http://hypernews.slac.stanford.edu/HyperNews/geant4/get/AUX/2010/02/23/07.51-21298-undAllDirIdenProcType.png

4)Another thing that I did was fix the properties of the surface between the

crystal and the mainBox and modify the properties of the surface between the

crystal and the apd. What I observed is that with one million of optical

photons, I detect about 48%(no difference between dielectric_metal or

dielectric_dielectric) for all the cases less the polishedbackpainted, ground

 and groundbackpainted, here I did not detect anything. Is this the usual?

Thank you so much!

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1 Feedback: Re: Explanation for the number of optical photons detected in an apd   (Gumplinger Peter - 23 Feb, 2010)
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