CInterface(InitialMaterialManager, FinalMaterialManager)
  CInterface(InitialMaterialManager, FinalMaterialManager, fWavelength)
  CInterface('vacuum', FinalMaterialManager, ...)
  CInterface(InitialMaterialManager, 'vacuum', ...)
  if fWavelength is not set uses wl depengent refractive index
  calculates n at fWavelength otherwise