0

On page 348 of the geant4 User’s guide and applications manual (refer to following link) http://ftp.tku.edu.tw/Linux/Gentoo/distfiles/BookForAppliDev-4.10.03.pdf

it states that "Pol01 - interaction of polarized beam (e.g. circularly polarized photons) with polarized target"

On lines 25 and 26 in the histo.mac file of the Pol01 example it has the following two lines of instructions...

/gun/polarization 0. 0. -1.

/gun/particle gamma

The direction of this gamma beam is along the z-axis, and so, assuming the code is correct, the first line of code cannot be describing the polarization state of the electric field. Am I to take it then that, in this context, the first line defines the photon spin projection, and therefore it is defining a circularly polarized photon, either left or right depending on which convention geant4 uses?

eyllanesc
  • 235,170
  • 19
  • 170
  • 241
Quantum Kid
  • 11
  • 2

1 Answers1

0

Reading the code, Geant4 treats the three vector you use in /gun/polarization for a photon as the S1,S2,S3 components of a Stokes vector in calculations described in the Wikipedia article below.

https://en.wikipedia.org/wiki/Stokes_parameters

A (0,0,1) vector will represent circularly polarized light.

possum
  • 1,837
  • 3
  • 9
  • 18
  • Dear possum, Thank you for the reply. What you said makes sense but how do you know for sure that Geant4 uses Stokes vector representation? I mean, have you actually read it in a Geant4 manual? Because, so far, I haven't seen it written anywhere in any geant4 manual. Thanks again for the response. – Quantum Kid Oct 01 '20 at 01:16
  • I followed the gun polarization into the source of the the polarization processes, e.g. http://www.apc.univ-paris7.fr/~franco/g4doxy/html/G4PolarizedComptonModel_8cc-source.html Where it sets it to a G4StokesVector and the formulae in the process are consistent with that use. To reinforce that, if you look at some talks by the author, they also use this formalism when describing their work. https://www.zeuthen.desy.de/ILC/polarisation/publications_talks/thepubsandtalks/schaelicke_ecfa05.pdf – possum Oct 01 '20 at 11:05
  • Thank you so much for your investigation. It is very much appreciated. You have completely answered my question. – Quantum Kid Oct 03 '20 at 02:10