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Keywords: optical photon boolean subtraction
Forum: Processes Involving Optical Photons
Re: Feedback Re: Optical problem with geometry subtraction (Gumplinger Peter)
Re: More Re: Optical problem with geometry subtraction (Gumplinger Peter)
Date: 26 Mar, 2007
From: Gumplinger Peter <Gumplinger Peter>

Whitney builds an elliptical mirror:

 G4Ellipsoid * ellipsoidMirrorOutside = new G4Ellipsoid("farmirror Ellipsoid outside",
       farToroidalAxisRadius+farToroidalTubeRadius+mirrorThickness ,
       farToroidalAxisRadius+ farToroidalTubeRadius+mirrorThickness,
       farToroidalAxisRadius+ farToroidalTubeRadius+mirrorThickness );

 G4Ellipsoid * ellipsoidMirrorInside = new G4Ellipsoid("farmirror Ellipsoid inside",
       farToroidalAxisRadius+farToroidalTubeRadius,         farToroidalTubeRadius,

 G4SubtractionSolid * shell  = new G4SubtractionSolid("Outside - Inside Ellipsoid", ellipsoidMirrorOutside ,ellipsoidMirrorInside);

 G4Box* farMirrorBox2 = new G4Box("nearMirrorBox", xFarMirrorBox/2, yFarMirrorBox/2, (farToroidalAxisRadius)/2);

 G4IntersectionSolid * farMirrorGlassElliptical = new G4IntersectionSolid("3mm glass elliptical mirror", farMirrorBox2, shell,0,G4ThreeVector(0,0,-farToroidalAxisRadius-farToroidalTubeRadius));

 G4LogicalVolume * mirror_log = new G4LogicalVolume(farMirrorGlassElliptical, Glass,"sphere subtracted",0,0,0);
 G4VPhysicalVolume * mirror_phys = new G4PVPlacement(0,G4ThreeVector(0,0,0), mirror_log , "toroid phys",  expHall_log, false,0);

Now, when he launches an optical photon at this mirror:

* G4Track Information:   Particle = opticalphoton,   Track ID = 1,   Parent ID = 0

Step#      X         Y         Z        KineE    dEStep   StepLeng  TrakLeng    Volume     Process
  0      0 fm      0 fm     -2 m       3 eV      0 eV      0 fm      0 fm        World    initStep
Photon at Boundary!
Old Momentum Direction: (-0.0011909028,0.0030247129,0.99999472)
Old Polarization:       (-0.96734311,0.25346325,-0.0019186754)
New Momentum Direction: (0.0030773681,-0.015315891,-0.99987797)
New Polarization:       (0.96733257,-0.25341795,0.006858997)
*** SpikeReflection ***
  1  -2.38 mm   6.05 mm  -30.3 um      3 eV      0 eV      2 m       2 m         World  Transportation

everything fine till here, we have reflection off the mirror, just where we want it, but now:

Photon at Boundary!
Old Momentum Direction: (0.0030773681,-0.015315891,-0.99987797)
Old Polarization:       (0.96733257,-0.25341795,0.006858997)
New Momentum Direction: (0.0030773681,-0.015315891,-0.99987797)
New Polarization:       (0.79437319,0.6073913,-0.006858997)
*** FresnelRefraction ***
  2  -1.98 mm   4.07 mm  -12.9 cm      3 eV      0 eV   12.9 cm   2.13 m    toroid phys  Transportation
                                                                            THE PROBLEM
it should be 'World".

Since the photon finds itself inside 'toroid phys' it finds the extend (farMirrorBox2) and thus another boundary of it going the opposite direction.

He gets the same problem changing to G4Sphere; i.e. to a spherical mirror.

The problem is an incorrect reallocation after reflection of mirrors constructed this way. Can this G4 bug be fixed? Can he construct an ellipsoid mirror a different way?

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