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Question Refractive indices of painting materials 

Forum: Processes Involving Optical Photons
Date: 31 Jan, 2010
From: Akira Okumura <Akira Okumura>

Hello all,

I have a question about the refractive indices of painting materials and reflections at the boundaries.

When I construct a scintillator block with a "painted" boundary, as you know, we can choose 4 different types of painting. But I do not fully understand how reflections are treated at the boundary with each boundary types. I here write what I understand. I would like someone to correct it if I made any mistake.

I am assuming a scintillator block in air.

1) polishedfrontpainted

If G4BooleanRand(theReflectivity) == false, a photon is absorbed or detected. Otherwise, it is always "spike" reflected. Therefore, refractive indices of the block and painting is not used to calculate the reflectivity nor reflection angle.

2) groundfrontpainted

Exactly same as 1), but reflection is always Lambertian. sigma_alpha and polished parameters are ignored.

3) polishedbackpainted

Snell's law is used at the boundary where the refractive index 1 is chosen from the scintillator box, but the refractive index 2 is chosen from the material property table of the optical surface (i.e. not from the air).

Reflection and refraction process are calculated according to Snell's law. polished or sigma_alpha parameter is used at this stage to calculate the roughness of the boundary. If the direction of a refracted photon is coming inside the block, or the reflected photon is going outside the block, reflection/refraction calculation is done repeatedly. Thus multiple refraction/reflection may be occurred. ... (A)

Once a photon is transmitted to the outside of the box, it is "spike" reflected at the painting, unless it is absorbed or detected by the painting. Where, the distance between the boundary and painting is infinitely small.

After the reflection, the above process (A) is calculated again. This time, the photon goes from the outside to the inside of the box. Since the process (A) may cause a reflection at the boundary, "spike" reflection at the painting can be occurred again.

4) groundbackpainted

Exactly same as 3), but reflection at the painting is always Lambertian. sigma_alpha and polished parameters are ignored. The angular distribution of reflected photon is the combination of the Lambertian at the painting and the roughness (polished or sigma_alpha) at the boundary.


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1 Feedback: Re: Refractive indices of painting materials   (Gumplinger Peter - 01 Feb, 2010)
(_ Question: Re: Refractive indices of painting materials   (Akira Okumura - 02 Feb, 2010)
(_ Feedback: Re: Refractive indices of painting materials   (Gumplinger Peter - 03 Feb, 2010)
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