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Forum: Geometry
Re: Question Photon Propagation through 2 different material. (JungEun Elena Suh)
Date: 03 Dec, 2014
From: Gumplinger Peter <Gumplinger Peter>

> I have a radiator bar which made of fused silica.
> This is for studying Cherenkov radiation.

> Now I want to add a block of glass on the one side of radiator.
> This glass has higher refractive index than radiator.
> So, I though that photon should be propagated through the glass.
> However, this simulation doesn't finished for 2 whole days.

You should probably also specify an absorption length for your radiator and for the glass.

> I didn't set reflection & efficiency parameter of glass.

Fine

> I set border surface property between fused silica and glass,

In a first interation you don't even have to specify a surface. It is enought to set the index of refraction of both the radiator and the glass. In that case, the surface is set to be dielectric_dielectric and polished.

> the optical surface is as below.
> optsurface->SetType(dielectric_dielectric);
> optsurface->SetFinish(polished);
> opsurface->SetModel(unified);

OK! But perhaps use instead: SetModel(glisur);

> new G4LogicalBorderSurface("rad_glass",radiator,glass,optsurface);
> I didn't set any other surfaces.

Fine, except you should in principle define the surface for both directions:

radiator->glass and glass->radiator

> What can I do in this case?
> Should I set more parameters?

It looks like you need to set a finite absorption length. If you don't then an internal reflected photon can keep on reflecting in some cases without end. Just one such photon is enough to hang your program.

Peter

P.S. Optical photon questions are best asked in the dedicated forum.

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