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Forum: Processes Involving Optical Photons
Re: Question queries regarding border surfaces (Athreya Shankar)
Re: None Re: queries regarding border surfaces (Davinder Siwal)
Re: Question Re: queries regarding border surfaces (Athreya Shankar)
Date: 05 Dec, 2011
From: Gumplinger Peter <Gumplinger Peter>

Hi Athreya,

> What I wanted to ask was as both my detector and the outside world are
> vacuum, can I define their interface as dielectric_metal (using
> g4LogicalBordersurface)?

Yes, in fact if you were to define it as dielectric_dielectric you would get no reflexion at the interface because, in that case, the program checks whether the index of refraction of the two media are the same or not. If they are the same photons will go right through as they would according to Snell's Law.

> Or should I create an Al layer around the
> detector (using G4PhysicaVolume) and then define this new interface as
> dielectric_metal?

It is not necessary to actually define the 'metal' as a physical volume as far as simulation of the physics of optical photons is concerned.

> Also, I was thinking how can a photon just get absorbed at the cladding?

I suspect that you have not given the cladding an index of refraction. If a photon encounters a dielectric medium without an index, photons are 'killed'. This is done 'silently' unless you turn on:

theBoundaryProcess->SetVerboseLevel(1);

which I suggest you do anyway while you are debugging your program so you see exactly what is being simulated at your interfaces.

> I understand that whether it is reflected or refracted depends on
> Fresnel's laws. But how can it get absorbed?

ditto

> 2. I tried to model a PMT, and so I set the efficiency of the

> photocathode surface to 1 for a range of wavelengths.

The efficiency is the quantum efficiency, the probability of an absorbed photon to be 'detected'. You have to set the absorption probability to one first. This is done by setting the Reflectivity of the dielectric_metal surface to zero if you want all photons to be absorbed (it is one - perfectly reflective - by default).

> I understand that whether it is reflected or refracted depends on
> Fresnel's laws. But how can it get absorbed?

ditto

> Why does the photon not undergo OpWLS every time?

If you want all photons to be WLS in your fiber you need to set the WLS absorption length to be very short. For realistic fibers that isn't the case and photons may go right through a fiber without being trapped or WLS.

Peter

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1 None: Re: queries regarding border surfaces   (Athreya Shankar - 06 Dec, 2011)
(_ Feedback: Re: queries regarding border surfaces   (Gumplinger Peter - 06 Dec, 2011)
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