Message: Refractive indices of painting materials Not Logged In (login)
 Next-in-Thread Next-in-Thread
 Next-in-Forum Next-in-Forum

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.

Akira

Inline Depth:
 0 0
 1 1
Add message: (add)

Feedback Re: Refractive indices of painting materials  by Gumplinger Peter <Gumplinger Peter>,   01 Feb, 2010
Re: Question Refractive indices of painting materials (Akira Okumura)
Hello Akira,

1) correct

2) correct

3) polishedbackpainted - correct, except:

> 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.

should read:

Reflection and refraction process are calculated according to Snell's law. polished or sigma_alpha parameter is NOT used at this stage to calculate the roughness of the boundary since the boundary is assumed to be polished (same as the backpaint is also perfectly polished); e.g. the 'polished' attribute refers to both the interface (A) as well as the 'backpaint'.

4) correct

I think you have summarized it very well. The interface (A) is simulated as if there was no 'backpaint'; e.g. as in 'ground' If the interaction with (A) results in refraction (to the outside - for photons coming from the crystal) or reflection (back outside - for photons coming from the 'backpaint') these photons will again be reflected or absorbed at the Lambertian 'backpaint'. This goes on until the photon is refracted back into the crystal.

Peter

Question Re: Refractive indices of painting materials  by Akira Okumura <Akira Okumura>,   02 Feb, 2010
Re: Feedback Re: Refractive indices of painting materials (Gumplinger Peter)
Thank you so much Peter. Now the 4 different conditions are clear for me.

Then how can I implement a grind scintillator block wrapped with specular material sheet?

Feedback Re: Refractive indices of painting materials  by Gumplinger Peter <Gumplinger Peter>,   03 Feb, 2010
Re: Question Re: Refractive indices of painting materials (Akira Okumura)
> Then how can I implement a grind scintillator block wrapped with specular

> material sheet?

I am afraid this combination of "ground" dielectric_dielectric and specular ("polished") reflector is only possible if you actually implement the geometry with the gap and two surfaces scintillator/gap and gap/reflector (dielectric_metal).

However, if you have access to the G4 source, by modifying only one line, you can change the behaviour of 'groundbackpainted' to do what you want. Comment out:

http://www-geant4.kek.jp/lxr/source/processes/optical/src/G4OpBoundaryProcess.cc#L990

Then the logic in DoReflection will choose 'specular' instead of Lambertian.

I should be thinking of another user option to choose the back-reflector property in 'backpainted'.

Peter

 Add Message Add Message
to: "Refractive indices of painting materials"

 Subscribe Subscribe

This site runs SLAC HyperNews version 1.11-slac-98, derived from the original HyperNews