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Forum: Processes Involving Optical Photons
Re: Question Question about the photocathode simulation and how to Detect the photon? (Xiaodong Zhang)
Re: More Re: Question about the photocathode simulation and how to Detect the photon? (Xiaodong Zhang)
Re: Warning Re: Question about the photocathode simulation and how to Detect the photon? (Gumplinger Peter)
Date: 02 Apr, 2012
From: Xiaodong Zhang <Xiaodong Zhang>

Thanks peter for your quick response.

> 
> The code you posted looks correct to me. Of course, I don't know the
> numerical values you provided for the things like,
> realRefractiveIndex_Bialkali, imaginaryRefractiveIndex_Bialkali,
> quantumEfficiency_Bialkali, but I presume these are also reasonable and
> correct. 

I think I used the correct data.

> HOWEVER, seeing that you find the program returns:
> 
> > When I call the G4OpBoundaryProcess::GetStatus, I got return value of
> 
> > 12, means "TotalInternalReflection", instead of "Detection".
> 
> makes me very suspicious whether you haven't also run into an (apparent)
> bug that I also just recently discovered. Which version of G4 are you
> using?

I use Geant4.9.4.p01. Sorry, I think I made a mistake to decode the value of 12. In this version, I think it should mean "StepTooSmall" based on the definition below. By the way, I directly copied it from source in the installation directory.

enum G4OpBoundaryProcessStatus {  Undefined,
                                FresnelRefraction, FresnelReflection,
                                   TotalInternalReflection,
                                   LambertianReflection, LobeReflection,
                                   SpikeReflection, BackScattering,
                                   Absorption, Detection, NotAtBoundary,
                                   SameMaterial, StepTooSmall, NoRINDEX,
                                   PolishedLumirrorAirReflection,....

> 
> I have just reported a bug:
> 
> http://bugzilla-geant4.kek.jp/show_bug.cgi?id=1300
> 
> G4OpBoundaryProcess cannot work correctly if the geometry/navigator
> makes a mistake in providing it with the correct surface normal. Now, I
> don't know how this error, on its own, can cause your program to claim
> 'TotalInternalReflection' for a surface that is dielectric_metal (which
> should be impossible - total internal reflection is only possible
> between two dielectric media).
> 
> If you have access to the G4 source, I suggest you print out the
> local/global coordinates and the local/global normal (as suggested in my
> bug report) and see if those actually make sense to you for the
> orientation of the PMT cathode in question.
> 
>

I followed the instruction of "the bug report" you mentioned. And recompiled the system, I can repeat the problem.

My next question is that do you have a method to solve this problem?

For your reference, I upload my detector structure. Please see the attachment.

In this detector, three parts(YAP+AL; lightguide(glass_Al-reflector); photocathode+pmt-window) I used the same model: Glisur; Polished; Dielectric-metal. All of them I used the complex refractive indexes.

Note here: in the program I set the thickness of photocathode as 23 nm.

When I run the program, I saw the un-correct value

PMT-windows and Photocathode interface:

theLocalPoint: (-2.39593,-1.56864,1.15e-05)

theGlobalPoint: (0.644071,7.55136,-6.87) ====> correct

theLocalNormal: (-0,-0,-1) ====> correct

theGlobalNormal: (0,0,1)

PMTwindow_physV +++++++++++++++>>> PMT windows

Process name:Transportation

Length of this Step: 1.54227 mm =====> step length

6 +++++++++++++++++++++++++>>>> Status of boundary: SpikeReflection

av_2_impr_1_SDpixel_logV_pv_11 +++++>>>> Photocathode

Process name:Transportation

Length of tghis Step: 0 mm

12 =========================>>StepTooSmall

For other boundaries, the results are similar.

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1 None: Re: Question about the photocathode simulation and how to Detect the photon?   (Xiaodong Zhang - 03 Apr, 2012)
1 Feedback: Re: Question about the photocathode simulation and how to Detect the photon?   (Gumplinger Peter - 03 Apr, 2012)
(_ None: Re: Question about the photocathode simulation and how to Detect the photon?   (Xiaodong Zhang - 06 Apr, 2012)
2 Feedback: Re: Question about the photocathode simulation and how to Detect the photon?   (Gumplinger Peter - 03 Apr, 2012)
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