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## Explanation for the number of optical photons detected in an apd

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