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Forum: Processes Involving Optical Photons
Re: Question unexpected rise of light yield with increasing surface roughness (sigma_alpha) (Martin Goettlich)
Date: 04 Mar, 2011
From: Gumplinger Peter <Gumplinger Peter>

Hi Martin,

Your condition, groundbackpainted with specular lobe 100%, has in effect two surfaces where the direction of the photon relative to the fiber axis (skewness) changes on every reflection from the fiber mantle; the fiber roughness specified by sigma_alpha and then the Labertian reflection off the reflector. I don't know what to expect. Some years ago I read and reposted an interesting article on rays in fibers at:

http://trshare.triumf.ca/~gum/skewrays/oa3316.pdf

Reading this carefully may explain what happens. It may not be intuitive so MC is exactly what 'keeps one honest'. The physics of the simulation at each encounter is rather simple. Since you are telling us that the number of absorptions at the reflector decreases this would tell us that more rays are actually reflected off the dielectric_dielectric interface with the air gap than reflected out. Another interesting number would be to find out how often your rays actaully are encountering the surface before they hit the fiber ends for different sigma_alpha.

Hope this helps, Peter

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