Problem 677

Summary:	Lambertian reflection at polishedbackpainted surface
Product:	Geant4	Reporter:	skononov
Component:	processes/optical	Assignee:	gum
Status:	RESOLVED WORKSFORME
Severity:	normal
Priority:	P2
Version:	6.2
Hardware:	All
OS:	All

Description skononov 2004-10-12 04:35:27 CEST

Hi,
I got a curious effect when set polishedbackpainted finish and unified model for
optical surface. Sometimes photons are reflected with random angle
though the chosen model implies only plain reflection, either Fresnel reflection
at the boundary or reflection from the paint.
I think I found places in the source which cause this:
G4OpBoundaryProcess.cc: lines 547 and 621 where reflection from boundary is
considered. "if" statement checks only for polished type and omits
polishedbackpainted case. As a result Lambertian reflection is chosen.

Comment 1 gum 2004-10-14 15:29:59 CEST

Turns out, 'polishedbackpainted' works just fine for me.

Please note, although it exists as an option, 'polishedbackpainted' really does
not provide extra functionality and the result should be exactly the same as
'polishedfrontpainted'. In both cases, the reflected ray obeys (v_incident +
v_exit) dot normal = 0.