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Sad Optical photons propagating at c instead of group velocity 

Forum: Processes Involving Optical Photons
Date: 05 Jan, 2012
From: Douglas Roberts <Douglas Roberts>

I recently upgraded to GEANT 4.9.5 and have noticed that optical photons start to propagate 
at c instead of the group velocity after a boundary process.  I didn't see this problem in 4.9.3.

I'm simulating a quartz Cerenkov detector and timing is very important to us.

I've included a dump of the tracking verbose info for the first few steps.  You can see that the
photon originally has the correct velocity (~198 mm/ns) but after internal reflection it becomes c.  
The "mother" volume is air and the "QuartzShortBar" is quartz.

Any insight would be appreciated.

-Doug Roberts

*********************************************************************************************************
* G4Track Information:   Particle = opticalphoton,   Track ID = 1,   Parent ID = 0
*********************************************************************************************************
>>AlongStepDoIt (after all invocations):
++List of invoked processes
1) Transportation
++G4Step Information
Address of G4Track    : 0x7f95be3563a0
Step Length (mm)      : 29.75725924388906
Energy Deposit (MeV)  : 0
-----------------------------------------------------------------------
StepPoint Information               PreStep            PostStep
-----------------------------------------------------------------------
Position - x (mm)   :    68.76732937097549   66.35245954887652
Position - y (mm)   :    840.6493370682001              853.75
Position - z (mm)   :                    0  -26.60893669799117
Global Time (ns)    :                    0  0.1499299012086033
Local Time (ns)     :                    0  0.1499299012086033
Proper Time (ns)    :                    0                   0
Momentum Direct - x : -0.08115229303568591-0.08115229303568591
Momentum Direct - y :   0.4402509930241723  0.4402509930241723
Momentum Direct - z :  -0.8941998481750488 -0.8941998481750488
Momentum - x (MeV/c): -2.454049053463367e-07-2.454049053463367e-07
Momentum - y (MeV/c): 1.331321016699039e-061.331321016699039e-06
Momentum - z (MeV/c): -2.704064431125926e-06-2.704064431125926e-06
Total Energy (MeV)  : 3.024004574195116e-063.024004574195116e-06
Kinetic Energy (MeV): 3.024004574195116e-063.024004574195116e-06
Velocity (mm/ns)    :    198.4744804339371   198.4744804339371
Volume Name         : av_1_impr_5_DircQuartzShortBar_pv_5av_1_impr_5_DircQuartzShortBar_pv_5
Safety (mm)         :                    0               5e-10
Polarization - x    :   0.1620986296198043  0.1620986296198043
Polarization - y    :  -0.8793846727977818 -0.8793846727977818
Polarization - Z    :  -0.4476679925164628 -0.4476679925164628
Weight              :                    1                   1
Step Status         :            Undefined          Geom Limit
Process defined Step:            Undefined      Transportation
-----------------------------------------------------------------------
++List of secondaries generated (x,y,z,kE,t,PID):  No. of secodaries = 0
**PostStepDoIt (after all invocations):
++List of invoked processes
1) Transportation
2) OpAbsorption (Forced)
3) OpBoundary
++G4Step Information
Address of G4Track    : 0x7f95be3563a0
Step Length (mm)      : 29.75725924388906
Energy Deposit (MeV)  : 0
-----------------------------------------------------------------------
StepPoint Information               PreStep            PostStep
-----------------------------------------------------------------------
Position - x (mm)   :    68.76732937097549   66.35245954887652
Position - y (mm)   :    840.6493370682001              853.75
Position - z (mm)   :                    0  -26.60893669799117
Global Time (ns)    :                    0  0.1499299012086033
Local Time (ns)     :                    0  0.1499299012086033
Proper Time (ns)    :                    0                   0
Momentum Direct - x : -0.08115229303568591-0.08115229303568591
Momentum Direct - y :   0.4402509930241723 -0.4402509930241723
Momentum Direct - z :  -0.8941998481750488 -0.8941998481750488
Momentum - x (MeV/c): -2.454049053463367e-07-2.454049053463367e-07
Momentum - y (MeV/c): 1.331321016699039e-06-1.331321016699039e-06
Momentum - z (MeV/c): -2.704064431125926e-06-2.704064431125926e-06
Total Energy (MeV)  : 3.024004574195116e-063.024004574195116e-06
Kinetic Energy (MeV): 3.024004574195116e-063.024004574195116e-06
Velocity (mm/ns)    :    198.4744804339371   198.4744804339371
Volume Name         : av_1_impr_5_DircQuartzShortBar_pv_5    DircBarBoxMother
Safety (mm)         :                    0               5e-10
Polarization - x    :   0.1620986296198043 -0.1620986296198043
Polarization - y    :  -0.8793846727977818 -0.8793846727977818
Polarization - Z    :  -0.4476679925164628  0.4476679925164628
Weight              :                    1                   1
Step Status         :            Undefined          Geom Limit
Process defined Step:            Undefined      Transportation
-----------------------------------------------------------------------
++List of secondaries generated (x,y,z,kE,t,PID):  No. of secodaries = 0
[Note]Secondaries from AlongStepDoIt included.
#Step#      X      Y      Z      KinE    dEStep    StepLen   TrackLen     Volume    Process
1   6.64 cm   85.4 cm  -2.66 cm   3.02 eV      0 eV   2.98 cm   2.98 cm  av_1_impr_5_DircQuartzShortBar_pv_5 Transportation
Velocity (entered Quartz) = 198.474
Step Length = 29.7573
Delta Time = 0.14993
Implied velocity = 198.474
>>AlongStepDoIt (after all invocations):
++List of invoked processes
1) Transportation
++G4Step Information
Address of G4Track    : 0x7f95be3563a0
Step Length (mm)      : 0
Energy Deposit (MeV)  : 0
-----------------------------------------------------------------------
StepPoint Information               PreStep            PostStep
-----------------------------------------------------------------------
Position - x (mm)   :    66.35245954887652   66.35245954887652
Position - y (mm)   :               853.75              853.75
Position - z (mm)   :   -26.60893669799117  -26.60893669799117
Global Time (ns)    :   0.1499299012086033  0.1499299012086033
Local Time (ns)     :   0.1499299012086033  0.1499299012086033
Proper Time (ns)    :                    0                   0
Momentum Direct - x : -0.08115229303568591-0.08115229303568591
Momentum Direct - y :  -0.4402509930241723 -0.4402509930241723
Momentum Direct - z :  -0.8941998481750488 -0.8941998481750488
Momentum - x (MeV/c): -2.454049053463367e-07-2.454049053463367e-07
Momentum - y (MeV/c): -1.331321016699039e-06-1.331321016699039e-06
Momentum - z (MeV/c): -2.704064431125926e-06-2.704064431125926e-06
Total Energy (MeV)  : 3.024004574195116e-063.024004574195116e-06
Kinetic Energy (MeV): 3.024004574195116e-063.024004574195116e-06
Velocity (mm/ns)    :    198.4744804339371   198.4744804339371
Volume Name         :     DircBarBoxMother    DircBarBoxMother
Safety (mm)         :                5e-10               5e-10
Polarization - x    :  -0.1620986296198043 -0.1620986296198043
Polarization - y    :  -0.8793846727977818 -0.8793846727977818
Polarization - Z    :   0.4476679925164628  0.4476679925164628
Weight              :                    1                   1
Step Status         :           Geom Limit          Geom Limit
Process defined Step:       Transportation      Transportation
-----------------------------------------------------------------------
++List of secondaries generated (x,y,z,kE,t,PID):  No. of secodaries = 0
**PostStepDoIt (after all invocations):
++List of invoked processes
1) Transportation
2) OpAbsorption (Forced)
3) OpBoundary
++G4Step Information
Address of G4Track    : 0x7f95be3563a0
Step Length (mm)      : 0
Energy Deposit (MeV)  : 0
-----------------------------------------------------------------------
StepPoint Information               PreStep            PostStep
-----------------------------------------------------------------------
Position - x (mm)   :    66.35245954887652   66.35245954887652
Position - y (mm)   :               853.75              853.75
Position - z (mm)   :   -26.60893669799117  -26.60893669799117
Global Time (ns)    :   0.1499299012086033  0.1499299012086033
Local Time (ns)     :   0.1499299012086033  0.1499299012086033
Proper Time (ns)    :                    0                   0
Momentum Direct - x : -0.08115229303568591-0.08115229303568591
Momentum Direct - y :  -0.4402509930241723 -0.4402509930241723
Momentum Direct - z :  -0.8941998481750488 -0.8941998481750488
Momentum - x (MeV/c): -2.454049053463367e-07-2.454049053463367e-07
Momentum - y (MeV/c): -1.331321016699039e-06-1.331321016699039e-06
Momentum - z (MeV/c): -2.704064431125926e-06-2.704064431125926e-06
Total Energy (MeV)  : 3.024004574195116e-063.024004574195116e-06
Kinetic Energy (MeV): 3.024004574195116e-063.024004574195116e-06
Velocity (mm/ns)    :    198.4744804339371          299.792458
Volume Name         :     DircBarBoxMotherav_1_impr_5_DircQuartzShortBar_pv_5
Safety (mm)         :                5e-10               5e-10
Polarization - x    :  -0.1620986296198043 -0.1620986296198043
Polarization - y    :  -0.8793846727977818 -0.8793846727977818
Polarization - Z    :   0.4476679925164628  0.4476679925164628
Weight              :                    1                   1
Step Status         :           Geom Limit          Geom Limit
Process defined Step:       Transportation      Transportation
-----------------------------------------------------------------------
++List of secondaries generated (x,y,z,kE,t,PID):  No. of secodaries = 0
[Note]Secondaries from AlongStepDoIt included.
#Step#      X      Y      Z      KinE    dEStep    StepLen   TrackLen     Volume    Process
2   6.64 cm   85.4 cm  -2.66 cm   3.02 eV      0 eV      0 fm   2.98 cm  DircBarBoxMother Transportation
>>AlongStepDoIt (after all invocations):
++List of invoked processes
1) Transportation
++G4Step Information
Address of G4Track    : 0x7f95be3563a0
Step Length (mm)      : 39.18219441484116
Energy Deposit (MeV)  : 0
-----------------------------------------------------------------------
StepPoint Information               PreStep            PostStep
-----------------------------------------------------------------------
Position - x (mm)   :    66.35245954887652   63.17273462594212
Position - y (mm)   :               853.75               836.5
Position - z (mm)   :   -26.60893669799117  -61.64564899490738
Global Time (ns)    :   0.1499299012086033  0.2806276334872491
Local Time (ns)     :   0.1499299012086033  0.2806276334872491
Proper Time (ns)    :                    0                   0
Momentum Direct - x : -0.08115229303568591-0.08115229303568591
Momentum Direct - y :  -0.4402509930241723 -0.4402509930241723
Momentum Direct - z :  -0.8941998481750488 -0.8941998481750488
Momentum - x (MeV/c): -2.454049053463367e-07-2.454049053463367e-07
Momentum - y (MeV/c): -1.331321016699039e-06-1.331321016699039e-06
Momentum - z (MeV/c): -2.704064431125926e-06-2.704064431125926e-06
Total Energy (MeV)  : 3.024004574195116e-063.024004574195116e-06
Kinetic Energy (MeV): 3.024004574195116e-063.024004574195116e-06
Velocity (mm/ns)    :           299.792458          299.792458
Volume Name         : av_1_impr_5_DircQuartzShortBar_pv_5av_1_impr_5_DircQuartzShortBar_pv_5
Safety (mm)         :                5e-10               5e-10
Polarization - x    :  -0.1620986296198043 -0.1620986296198043
Polarization - y    :  -0.8793846727977818 -0.8793846727977818
Polarization - Z    :   0.4476679925164628  0.4476679925164628
Weight              :                    1                   1
Step Status         :           Geom Limit          Geom Limit
Process defined Step:       Transportation      Transportation
-----------------------------------------------------------------------
++List of secondaries generated (x,y,z,kE,t,PID):  No. of secodaries = 0
**PostStepDoIt (after all invocations):
++List of invoked processes
1) Transportation
2) OpAbsorption (Forced)
3) OpBoundary
++G4Step Information
Address of G4Track    : 0x7f95be3563a0
Step Length (mm)      : 39.18219441484116
Energy Deposit (MeV)  : 0
-----------------------------------------------------------------------
StepPoint Information               PreStep            PostStep
-----------------------------------------------------------------------
Position - x (mm)   :    66.35245954887652   63.17273462594212
Position - y (mm)   :               853.75               836.5
Position - z (mm)   :   -26.60893669799117  -61.64564899490738
Global Time (ns)    :   0.1499299012086033  0.2806276334872491
Local Time (ns)     :   0.1499299012086033  0.2806276334872491
Proper Time (ns)    :                    0                   0
Momentum Direct - x : -0.08115229303568591-0.08115229303568591
Momentum Direct - y :  -0.4402509930241723  0.4402509930241723
Momentum Direct - z :  -0.8941998481750488 -0.8941998481750488
Momentum - x (MeV/c): -2.454049053463367e-07-2.454049053463367e-07
Momentum - y (MeV/c): -1.331321016699039e-061.331321016699039e-06
Momentum - z (MeV/c): -2.704064431125926e-06-2.704064431125926e-06
Total Energy (MeV)  : 3.024004574195116e-063.024004574195116e-06
Kinetic Energy (MeV): 3.024004574195116e-063.024004574195116e-06
Velocity (mm/ns)    :           299.792458   198.4744804339371
Volume Name         : av_1_impr_5_DircQuartzShortBar_pv_5    DircBarBoxMother
Safety (mm)         :                5e-10               5e-10
Polarization - x    :  -0.1620986296198043  0.1620986296198043
Polarization - y    :  -0.8793846727977818 -0.8793846727977818
Polarization - Z    :   0.4476679925164628 -0.4476679925164628
Weight              :                    1                   1
Step Status         :           Geom Limit          Geom Limit
Process defined Step:       Transportation      Transportation
-----------------------------------------------------------------------
++List of secondaries generated (x,y,z,kE,t,PID):  No. of secodaries = 0
[Note]Secondaries from AlongStepDoIt included.
#Step#      X      Y      Z      KinE    dEStep    StepLen   TrackLen     Volume    Process
3   6.32 cm   83.7 cm  -6.16 cm   3.02 eV      0 eV   3.92 cm   6.89 cm  av_1_impr_5_DircQuartzShortBar_pv_5 Transportation
>>AlongStepDoIt (after all invocations):
++List of invoked processes
1) Transportation
++G4Step Information
Address of G4Track    : 0x7f95be3563a0
Step Length (mm)      : 0
Energy Deposit (MeV)  : 0
-----------------------------------------------------------------------
StepPoint Information               PreStep            PostStep
-----------------------------------------------------------------------
Position - x (mm)   :    63.17273462594212   63.17273462594212
Position - y (mm)   :                836.5               836.5
Position - z (mm)   :   -61.64564899490738  -61.64564899490738
Global Time (ns)    :   0.2806276334872491  0.2806276334872491
Local Time (ns)     :   0.2806276334872491  0.2806276334872491
Proper Time (ns)    :                    0                   0
Momentum Direct - x : -0.08115229303568591-0.08115229303568591
Momentum Direct - y :   0.4402509930241723  0.4402509930241723
Momentum Direct - z :  -0.8941998481750488 -0.8941998481750488
Momentum - x (MeV/c): -2.454049053463367e-07-2.454049053463367e-07
Momentum - y (MeV/c): 1.331321016699039e-061.331321016699039e-06
Momentum - z (MeV/c): -2.704064431125926e-06-2.704064431125926e-06
Total Energy (MeV)  : 3.024004574195116e-063.024004574195116e-06
Kinetic Energy (MeV): 3.024004574195116e-063.024004574195116e-06
Velocity (mm/ns)    :    198.4744804339371   198.4744804339371
Volume Name         :     DircBarBoxMother    DircBarBoxMother
Safety (mm)         :                5e-10               5e-10
Polarization - x    :   0.1620986296198043  0.1620986296198043
Polarization - y    :  -0.8793846727977818 -0.8793846727977818
Polarization - Z    :  -0.4476679925164628 -0.4476679925164628
Weight              :                    1                   1
Step Status         :           Geom Limit          Geom Limit
Process defined Step:       Transportation      Transportation
-----------------------------------------------------------------------
++List of secondaries generated (x,y,z,kE,t,PID):  No. of secodaries = 0
**PostStepDoIt (after all invocations):
++List of invoked processes
1) Transportation
2) OpAbsorption (Forced)
3) OpBoundary
++G4Step Information
Address of G4Track    : 0x7f95be3563a0
Step Length (mm)      : 0
Energy Deposit (MeV)  : 0
-----------------------------------------------------------------------
StepPoint Information               PreStep            PostStep
-----------------------------------------------------------------------
Position - x (mm)   :    63.17273462594212   63.17273462594212
Position - y (mm)   :                836.5               836.5
Position - z (mm)   :   -61.64564899490738  -61.64564899490738
Global Time (ns)    :   0.2806276334872491  0.2806276334872491
Local Time (ns)     :   0.2806276334872491  0.2806276334872491
Proper Time (ns)    :                    0                   0
Momentum Direct - x : -0.08115229303568591-0.08115229303568591
Momentum Direct - y :   0.4402509930241723  0.4402509930241723
Momentum Direct - z :  -0.8941998481750488 -0.8941998481750488
Momentum - x (MeV/c): -2.454049053463367e-07-2.454049053463367e-07
Momentum - y (MeV/c): 1.331321016699039e-061.331321016699039e-06
Momentum - z (MeV/c): -2.704064431125926e-06-2.704064431125926e-06
Total Energy (MeV)  : 3.024004574195116e-063.024004574195116e-06
Kinetic Energy (MeV): 3.024004574195116e-063.024004574195116e-06
Velocity (mm/ns)    :    198.4744804339371          299.792458
Volume Name         :     DircBarBoxMotherav_1_impr_5_DircQuartzShortBar_pv_5
Safety (mm)         :                5e-10               5e-10
Polarization - x    :   0.1620986296198043  0.1620986296198043
Polarization - y    :  -0.8793846727977818 -0.8793846727977818
Polarization - Z    :  -0.4476679925164628 -0.4476679925164628
Weight              :                    1                   1
Step Status         :           Geom Limit          Geom Limit
Process defined Step:       Transportation      Transportation
-----------------------------------------------------------------------

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1 Agree: Re: Optical photons propagating at c instead of group velocity   (Gumplinger Peter - 08 Jan, 2012)
(_ More: Re: Optical photons propagating at c instead of group velocity   (Gumplinger Peter - 24 Jan, 2012)
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