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Forum: Processes Involving Optical Photons
Re: Question Coat a quartz cylinder with aluminium. (JungEun Elena Suh)
Date: 26 May, 2014
From: Gumplinger Peter <Gumplinger Peter>

Hi JungEun Elena Suh,

> I have a lump of quartz cylinder, and I want to coat it with aluminium.
> and some photons go though the quartz cylinder should be reflected by
> this aluminium.

What you want to do is surround your quartz cylinder with a 'dielectric_metal' surface. In this case, since the surface is not a dielectric_dielectric' you have to define a G4OpSurface etc. (please see the examples and documentation). What you do not necessarily have to implement - as far as optical photon tracking is concerned - is an actual aluminium volume (you do if you want to simulate incoming EM showers correctly or energy leaking out of the quarz).

> So, first I try to make another slightly bigger cylinder and subtract
> inside(quartz cylinder). And set the material as below.
> 
>   G4Material* Al = new G4Material("Aluminum", 13., 26.98*g/mole, 2.700*g/cm3);
>   G4double Al_PP[NUMENTRIES] = {5.0*eV, 6.69*eV, 7.50*eV};
>   G4double Al_refl[NUMENTRIES] = {1., 1., 1.,};

Do not add optical properties to the volume (Al) medium. It is a metal and does not have a pure real index of refraction.

> mptAl->AddProperty("REFLECTIVITY",Al_PP,Al_refl,NUMENTRIES);

Only a G4OpticalSurface's MaterialPropertiesTable is interrogated about its "REFLECTIVITY"

> However, some photons are penetrate Al mirror. Is it possible?

Yes, because the default surface is dielectric_dielectric and you gave a real (1.) index of refraction.

> change ABSL as < 0.01*cm, then this phenomenon is disappeared.

Yes, now the photons get absorbed quickly.

> Then it
> means those photons are not reflected but absorbed?

Yes

You need to define the surface of the quarz to be dielectric_metal and an associated G4OpticalSurface with an attached G4MaterialPropertiesTable. It's all in the documentation. See, the fiber mirrors in wls example:

http://www-geant4.kek.jp/lxr/source/examples/extended/optical/wls/src/WLSDetectorConstruction.cc#L173

Hope this helps, Peter

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