G4OpMieHG.cc

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////////////////////////////////////////////////////////////////////////
//
// File G4OpMieHG.hh
// Description: Discrete Process -- Mie Scattering of Optical Photons
// Created: 2010-07-03
// Author: Xin Qian
// Based on work from Vlasios Vasileiou
//
// This subroutine will mimic the Mie scattering based on
// Henyey-Greenstein phase function
// Forward and backward angles are treated separately.
//
////////////////////////////////////////////////////////////////////////
 
#include "G4OpMieHG.hh"
#include "G4PhysicalConstants.hh"
#include "G4OpticalParameters.hh"
#include "G4OpProcessSubType.hh"
 
//....oooOO0OOooo........oooOO0OOooo........oooOO0OOooo........oooOO0OOooo......
G4OpMieHG::G4OpMieHG(const G4String& processName, G4ProcessType type)
  : G4VDiscreteProcess(processName, type)
{
  Initialise();
  if(verboseLevel > 0)
  {
    G4cout << GetProcessName() << " is created " << G4endl;
  }
  SetProcessSubType(fOpMieHG);
}
 
//....oooOO0OOooo........oooOO0OOooo........oooOO0OOooo........oooOO0OOooo......
G4OpMieHG::~G4OpMieHG() {}
 
//....oooOO0OOooo........oooOO0OOooo........oooOO0OOooo........oooOO0OOooo......
void G4OpMieHG::PreparePhysicsTable(const G4ParticleDefinition&)
{
  Initialise();
}
 
//....oooOO0OOooo........oooOO0OOooo........oooOO0OOooo........oooOO0OOooo......
void G4OpMieHG::Initialise()
{
  SetVerboseLevel(G4OpticalParameters::Instance()->GetMieVerboseLevel());
}
 
//....oooOO0OOooo........oooOO0OOooo........oooOO0OOooo........oooOO0OOooo......
G4VParticleChange* G4OpMieHG::PostStepDoIt(const G4Track& aTrack,
                                           const G4Step& aStep)
{
  aParticleChange.Initialize(aTrack);
 
  const G4DynamicParticle* aParticle = aTrack.GetDynamicParticle();
  const G4MaterialPropertiesTable* MPT =
    aTrack.GetMaterial()->GetMaterialPropertiesTable();
 
  G4double forwardRatio = MPT->GetConstProperty(kMIEHG_FORWARD_RATIO);
 
  if(verboseLevel > 1)
  {
    G4cout << "OpMie Scattering Photon!" << G4endl
           << " Old Momentum Direction: " << aParticle->GetMomentumDirection()
           << G4endl
           << " MIE Old Polarization: " << aParticle->GetPolarization()
           << G4endl;
  }
 
  G4double gg;
  G4int direction;
  if(G4UniformRand() <= forwardRatio)
  {
    gg        = MPT->GetConstProperty(kMIEHG_FORWARD);
    direction = 1;
  }
  else
  {
    gg        = MPT->GetConstProperty(kMIEHG_BACKWARD);
    direction = -1;
  }
 
  G4double r = G4UniformRand();
 
  // sample the direction
  G4double theta;
  if(gg != 0.)
  {
    theta = std::acos(2. * r * (1. + gg) * (1. + gg) * (1. - gg + gg * r) /
                        ((1. - gg + 2. * gg * r) * (1. - gg + 2. * gg * r)) -
                      1.);
  }
  else
  {
    theta = std::acos(2. * r - 1.);
  }
  G4double phi = G4UniformRand() * twopi;
 
  if(direction == -1)
    theta = pi - theta;  // backward scattering
 
  G4ThreeVector newMomDir, oldMomDir;
  G4ThreeVector newPol, oldPol;
 
  G4double sinth = std::sin(theta);
  newMomDir.set(sinth * std::cos(phi), sinth * std::sin(phi), std::cos(theta));
  oldMomDir = aParticle->GetMomentumDirection();
  newMomDir.rotateUz(oldMomDir);
  newMomDir = newMomDir.unit();
 
  oldPol = aParticle->GetPolarization();
  newPol = newMomDir - oldPol / newMomDir.dot(oldPol);
  newPol = newPol.unit();
 
  if(newPol.mag() == 0.)
  {
    r = G4UniformRand() * twopi;
    newPol.set(std::cos(r), std::sin(r), 0.);
    newPol.rotateUz(newMomDir);
  }
  else
  {
    // There are two directions perpendicular to new momentum direction
    if(G4UniformRand() < 0.5)
      newPol = -newPol;
  }
 
  aParticleChange.ProposePolarization(newPol);
  aParticleChange.ProposeMomentumDirection(newMomDir);
 
  if(verboseLevel > 1)
  {
    G4cout << "OpMie New Polarization: " << newPol << G4endl
           << " Polarization Change: " << *(aParticleChange.GetPolarization())
           << G4endl << " New Momentum Direction: " << newMomDir << G4endl
           << " Momentum Change: " << *(aParticleChange.GetMomentumDirection())
           << G4endl;
  }
 
  return G4VDiscreteProcess::PostStepDoIt(aTrack, aStep);
}
 
//....oooOO0OOooo........oooOO0OOooo........oooOO0OOooo........oooOO0OOooo......
G4double G4OpMieHG::GetMeanFreePath(const G4Track& aTrack, G4double,
                                    G4ForceCondition*)
{
  G4double attLength = DBL_MAX;
  G4MaterialPropertiesTable* MPT =
    aTrack.GetMaterial()->GetMaterialPropertiesTable();
  if(MPT)
  {
    G4MaterialPropertyVector* attVector = MPT->GetProperty(kMIEHG);
    if(attVector)
    {
      attLength = attVector->Value(
        aTrack.GetDynamicParticle()->GetTotalEnergy(), idx_mie);
    }
  }
  return attLength;
}