CEnvelope(sName, hSpace)
 CEnvelope(sName, hSpace, fReferenceWavelength)
 CEnvelope(sName, hSpace, fReferenceWavelength, sPolarization)
 CEnvelope(sFileName) - load from file (has its own space)
 sPolarization = 'o', 'e' for uniaxial and, 's', 'f' for biaxial
 sPolarization = 'o' for non birefringent