OpBoundaryProcessSimple.cxx

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// Adapted for LArSoft by Ben Jones, MIT, March 2010
//
// This class invokes a simplified model of optical reflections at
// boundaries between different materials.  The relevant reflectivities
// are read in by an implementation of the MaterialPropertiesLoader.
//
// The required parameters are total reflectance and ratio of diffuse
// to specular reflectance.  Each photon crossing a boundary with a
// defined reflectance is randomly either reflected or absorbed and killed
// according to the supplied probability.
//
// Every reflected photon with a defined diffuse reflection fraction
// is then randomly either diffusely or specularly reflected according
// to the supplied probability.  All materials with no defined
// reflectance are assumed to be black and
//  absorb all incident photons.
//
// This physics process is loaded in the OpticalPhysics physics constructor.
//
// This class is based on the G4OpBoundaryProcess class in Geant4

//
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//
// Optical Photon Boundary Process Class Implementation

#include "art/Framework/Services/Registry/ServiceHandle.h"

#include "Geant4/G4GeometryTolerance.hh"
#include "Geant4/G4Navigator.hh"
#include "Geant4/G4OpProcessSubType.hh"
#include "Geant4/G4RandomTools.hh"
#include "Geant4/G4TransportationManager.hh"
#include "Geant4/G4ios.hh"

#include "larsim/LegacyLArG4/OpBoundaryProcessSimple.hh"
#include "larsim/Simulation/LArG4Parameters.h"

//#define G4DEBUG_OPTICAL

namespace larg4 {

  OpBoundaryProcessSimple::OpBoundaryProcessSimple(const G4String& processName, G4ProcessType type)
    : G4VDiscreteProcess(processName, type)
  {
    G4cout << GetProcessName() << " is created " << G4endl;

    SetProcessSubType(fOpBoundary);

    fTheStatus = Undefined;

    fCarTolerance = G4GeometryTolerance::GetInstance()->GetSurfaceTolerance();
  }

  //Action to take after making each step of an optical photon - described in file header.

  // PostStepDoIt
  G4VParticleChange* OpBoundaryProcessSimple::PostStepDoIt(const G4Track& aTrack,
                                                           const G4Step& aStep)
  {

    // Note - these have to be loaded here, since this object
    // is constructed before LArG4, and hence before the
    // LArG4 parameters are read from config

    fTheStatus = Undefined;
    aParticleChange.Initialize(aTrack);

    G4StepPoint* pPreStepPoint = aStep.GetPreStepPoint();
    G4StepPoint* pPostStepPoint = aStep.GetPostStepPoint();

    if (pPostStepPoint->GetStepStatus() != fGeomBoundary) {
      fTheStatus = NotAtBoundary;
      return G4VDiscreteProcess::PostStepDoIt(aTrack, aStep);
    }
    if (aTrack.GetStepLength() <= fCarTolerance / 2) {
      fTheStatus = StepTooSmall;
      return G4VDiscreteProcess::PostStepDoIt(aTrack, aStep);
    }

    G4Material* Material1 = pPreStepPoint->GetMaterial();
    G4Material* Material2 = pPostStepPoint->GetMaterial();

    if (Material1 != Material2) {

      art::ServiceHandle<sim::LArG4Parameters const> lgp;

      fVerbosity = lgp->OpVerbosity();

      G4ThreeVector NewMomentum;
      G4ThreeVector NewPolarization;

      G4ThreeVector theGlobalNormal;
      G4ThreeVector theFacetNormal;

      std::string Material1Name = Material1->GetName();
      std::string Material2Name = Material2->GetName();

      const G4DynamicParticle* aParticle = aTrack.GetDynamicParticle();
      G4double thePhotonMomentum = aParticle->GetTotalMomentum();
      G4ThreeVector OldMomentum = aParticle->GetMomentumDirection();
      G4ThreeVector OldPolarization = aParticle->GetPolarization();

      if (fVerbosity > 9)
        std::cout << "OpBoundaryProcessSimple Debug: Photon " << aTrack.GetTrackID() << " momentum "
                  << thePhotonMomentum << " Material1 " << Material1Name.c_str() << " Material 2 "
                  << Material2Name.c_str() << std::endl;

      G4ThreeVector theGlobalPoint = pPostStepPoint->GetPosition();

      G4Navigator* theNavigator =
        G4TransportationManager::GetTransportationManager()->GetNavigatorForTracking();

      G4ThreeVector theLocalPoint =
        theNavigator->GetGlobalToLocalTransform().TransformPoint(theGlobalPoint);

      // Normal points back into volume
      G4bool valid;
      G4ThreeVector theLocalNormal = theNavigator->GetLocalExitNormal(&valid);

      if (valid) { theLocalNormal = -theLocalNormal; }
      else {
        G4cerr << " OpBoundaryProcessSimple/PostStepDoIt(): "
               << " The Navigator reports that it returned an invalid normal" << G4endl;
      }

      theGlobalNormal = theNavigator->GetLocalToGlobalTransform().TransformAxis(theLocalNormal);

      if (OldMomentum * theGlobalNormal > 0.0) {
#ifdef G4DEBUG_OPTICAL
        G4cerr << " OpBoundaryProcessSimple/PostStepDoIt(): "
               << " theGlobalNormal points the wrong direction " << G4endl;
#endif
        theGlobalNormal = -theGlobalNormal;
      }

      G4MaterialPropertiesTable* aMaterialPropertiesTable;
      G4MaterialPropertyVector* Reflectance;
      G4MaterialPropertyVector* DiffuseReflectanceFraction;

      aMaterialPropertiesTable = Material1->GetMaterialPropertiesTable();

      if (aMaterialPropertiesTable) {

        std::stringstream PropertyName;
        PropertyName << "REFLECTANCE_" << Material2Name.c_str();
        Reflectance = aMaterialPropertiesTable->GetProperty(PropertyName.str().c_str());

        PropertyName.str("");
        PropertyName << "DIFFUSE_REFLECTANCE_FRACTION_" << Material2Name.c_str();
        DiffuseReflectanceFraction =
          aMaterialPropertiesTable->GetProperty(PropertyName.str().c_str());

        if (Reflectance) {
          double theReflectance = Reflectance->Value(thePhotonMomentum);
          if (G4BooleanRand(theReflectance)) {
            if (DiffuseReflectanceFraction) {
              double theDiffuseReflectanceFraction =
                DiffuseReflectanceFraction->Value(thePhotonMomentum);
              if (G4BooleanRand(theDiffuseReflectanceFraction)) { fTheStatus = SimpleDiffuse; }
              else {
                fTheStatus = SimpleSpecular;
              }
            }
            else {
              fTheStatus = SimpleSpecular;
            }
          }
          else {
            fTheStatus = SimpleAbsorbed;
          }
        }
        else {
          fTheStatus = SimpleAbsorbedNoRefl;
        }
      }

      // Take action according to track status

      if (fTheStatus == SimpleDiffuse) {
        NewMomentum = G4LambertianRand(theGlobalNormal);
        theFacetNormal = (NewMomentum - OldMomentum).unit();
      }

      else if (fTheStatus == SimpleSpecular) {
        theFacetNormal = theGlobalNormal;
        G4double PdotN = OldMomentum * theFacetNormal;
        NewMomentum = OldMomentum - (2. * PdotN) * theFacetNormal;
      }

      else if ((fTheStatus == SimpleAbsorbed) || (fTheStatus == SimpleAbsorbedNoRefl)) {
        aParticleChange.ProposeTrackStatus(fStopAndKill);
      }

      else if ((fTheStatus == NotAtBoundary) || (fTheStatus == StepTooSmall)) {
        NewMomentum = OldMomentum;
      }
      else
        aParticleChange.ProposeTrackStatus(fStopAndKill);

      NewMomentum = NewMomentum.unit();
      aParticleChange.ProposeMomentumDirection(NewMomentum);
    }
    return G4VDiscreteProcess::PostStepDoIt(aTrack, aStep);
  }

  // Compulsary method for G4DiscreteProcesses.  Serves no actual function here.

  // GetMeanFreePath
  G4double OpBoundaryProcessSimple::GetMeanFreePath(const G4Track&,
                                                    G4double,
                                                    G4ForceCondition* condition)
  {
    *condition = Forced;

    return DBL_MAX;
  }
}