This application simulates the propagation of optical photons inside a Wave Length Shifting (WLS) fiber.

Geometry Definition

The default geometry is as follow:

A perfect, bare (or clad), PMMA fiber: 0.5mm radius, 2m length at center (0,0,0) of the World.
A circular MPPC with 0.5mm radius at the +z end of the fiber
World and coupling materials are G4_AIR
Photons will always refracted out to coupling material before reaching MPPC
There are many flexible parameters that the user could specify. They are under the /WLS directory of help.

Material Choices

There are several materials that the user can use for the fiber core, world and coupling.

They are:

Vacuum (G4_Galactic)
Air (G4_AIR)
PMMA, refractive index n = 1.60
Pethylene, n = 1.49
FPethylene, n = 1.42
Polystyrene, n = 1.60
Silicone, n = 1.46

Photon Source

This program uses the General Particle Source (G4GeneralParticleSource) provided by Geant4 for generating particles. The energy of a primary optical photon must be within the range 2.00 eV to 3.47 eV.

Hit

A hit is registered when an optical photon is absorbed on the MPPC surface. Information stored in a hit includes the local coordinate of the location the optical photon is absorbed on the MPPC, the global coordinate where the optical photon left the fiber, the transit time of the optical photon, and the energy of the optical photon.

Stepping Action

The stepping action keeps track of the number of bounces an optical photon has gone through. In order to prevent infinite loop and extremely skewed rays taking up computing time, there is a limit of the number of bounces that an optical photon can go through before it is artificially killed. The default limit is 100,000. The user can set his/her own limit using the /stepping/setBounceLimit command. A value of 0 will turn off the limit. All optical photons artificially killed will have murderee flag turned on in their UserTrackInformation.

Visualization

To visualize particle trajectories, simply use vis.mac macro in interactive mode or in your own macro.

main ()

Execute wls in 'batch' mode from macro files;
you can enter an optional integer seed for batch mode
```
% wls electron.mac (optional: enter an integer seed here)
```

wls in 'interactive mode' with visualization

% wls
....
Idle> /control/execute vis.mac
Idle> /run/beamOn 1
....
Idle> exit

Macros provided

electron.mac: Sets up the default geometry and configures the particle source. Primary particle is a 10 MeV electron.
vis.mac: macro for visualization; called automatically when no macro is given on command line.