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.
//
// mail:  gum@triumf.ca
//

#include "G4OpMieHG.hh"
#include "G4PhysicalConstants.hh"
#include "G4OpProcessSubType.hh"

//....oooOO0OOooo........oooOO0OOooo........oooOO0OOooo........oooOO0OOooo......

G4OpMieHG::G4OpMieHG(const G4String& processName, G4ProcessType type)
           : G4VDiscreteProcess(processName, type)
{
  if (verboseLevel>0) {
     G4cout << GetProcessName() << " is created " << G4endl;
  }

  SetProcessSubType(fOpMieHG);
}
//....oooOO0OOooo........oooOO0OOooo........oooOO0OOooo........oooOO0OOooo......

G4OpMieHG::~G4OpMieHG(){}

//....oooOO0OOooo........oooOO0OOooo........oooOO0OOooo........oooOO0OOooo......

G4VParticleChange*
G4OpMieHG::PostStepDoIt(const G4Track& aTrack, const G4Step& aStep)
{
  aParticleChange.Initialize(aTrack);

  const G4DynamicParticle* aParticle = aTrack.GetDynamicParticle();
  const G4Material* aMaterial = aTrack.GetMaterial();
  G4MaterialPropertiesTable* aMaterialPropertyTable =
    aMaterial->GetMaterialPropertiesTable();

  G4double forward_g =
              aMaterialPropertyTable->GetConstProperty(kMIEHG_FORWARD);
  G4double backward_g =
              aMaterialPropertyTable->GetConstProperty(kMIEHG_BACKWARD);
  G4double ForwardRatio =
              aMaterialPropertyTable->GetConstProperty(kMIEHG_FORWARD_RATIO);

  if (verboseLevel >0 ) {
    G4cout << "MIE Scattering Photon!" << G4endl;
    G4cout << "MIE Old Momentum Direction: "
             << aParticle->GetMomentumDirection() << G4endl;
    G4cout << "MIE Old Polarization: "
         << aParticle->GetPolarization() << G4endl;
  }

  G4double gg;
  G4int direction;
  if (G4UniformRand() <= ForwardRatio){
     gg = forward_g;
     direction = 1;
  } else {
     gg = backward_g;
     direction = -1;
  }

  G4double r = G4UniformRand();

  G4double Theta;
  //sample the direction
  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;
  //G4double Phi = G4UniformRand()*2*pi;

  if (direction == -1) Theta = pi - Theta; //backward scattering

  G4ThreeVector NewMomentumDirection, OldMomentumDirection;
  G4ThreeVector OldPolarization, NewPolarization;

  NewMomentumDirection.set
                 (std::sin(Theta)*std::cos(Phi), std::sin(Theta)*std::sin(Phi), std::cos(Theta));
  OldMomentumDirection = aParticle->GetMomentumDirection();
  NewMomentumDirection.rotateUz(OldMomentumDirection);
  NewMomentumDirection = NewMomentumDirection.unit();

  OldPolarization = aParticle->GetPolarization();
  G4double constant = -1./NewMomentumDirection.dot(OldPolarization);

  NewPolarization = NewMomentumDirection + constant*OldPolarization;
  NewPolarization = NewPolarization.unit();

  if (NewPolarization.mag() == 0.) {
    r = G4UniformRand()*twopi;
    NewPolarization.set(std::cos(r),std::sin(r),0.);
    NewPolarization.rotateUz(NewMomentumDirection);
  } else {
    // There are two directions which perpendicular
    // new momentum direction
    if (G4UniformRand() < 0.5) NewPolarization = -NewPolarization;
  }

  aParticleChange.ProposePolarization(NewPolarization);
  aParticleChange.ProposeMomentumDirection(NewMomentumDirection);

  if (verboseLevel > 0) {
    G4cout << "MIE New Polarization: " << NewPolarization << G4endl;
    G4cout << "MIE Polarization Change: " << *(aParticleChange.GetPolarization()) << G4endl;
    G4cout << "MIE New Momentum Direction: " << NewMomentumDirection << G4endl;
    G4cout << "MIE Momentum Change: " << *(aParticleChange.GetMomentumDirection()) << G4endl;
  }

  return G4VDiscreteProcess::PostStepDoIt(aTrack, aStep);
}

//....oooOO0OOooo........oooOO0OOooo........oooOO0OOooo........oooOO0OOooo......

G4double G4OpMieHG::GetMeanFreePath(const G4Track& aTrack,
                                    G4double,
                                    G4ForceCondition*)
{
  const G4DynamicParticle* aParticle = aTrack.GetDynamicParticle();
  const G4Material* aMaterial = aTrack.GetMaterial();

  G4double thePhotonEnergy = aParticle->GetTotalEnergy();

  G4double AttenuationLength = DBL_MAX;

  G4MaterialPropertiesTable* aMaterialPropertyTable =
    aMaterial->GetMaterialPropertiesTable();

  if (aMaterialPropertyTable) {
    G4MaterialPropertyVector* AttenuationLengthVector =
                          aMaterialPropertyTable->GetProperty(kMIEHG);
    if (AttenuationLengthVector) {
        AttenuationLength = AttenuationLengthVector->Value(thePhotonEnergy);
    }
    // else {
    //          G4cout << "No Mie scattering length specified" << G4endl;
    //      }
  }
  //else {
  //         G4cout << "No Mie scattering length specified" << G4endl; 
  //     }

//  G4cout << thePhotonEnergy/GeV << " \t" << AttenuationLength/m << G4endl;

  return AttenuationLength;
}