Polarized spectroscopy of partially oriented molecules. A general formulation for two-photon processes in uniaxial samples

General expressions are given for linearly polarized intensity in a two-photon experiment on a uniaxial assembly of partially aligned molecules of arbitrary shape and symmetry, without any assumptions concerning the detailed nature of the uniaxial orientation distribution. The formulas are valid for electric dipole interactions and apply to measurements such as ordinary and resonant Raman scattering, two-photon absorption, photoluminescence, and transient or permanent photoinduced dichroism measured in stretched polymers, nematic liquid crystals, or lipid bilayers. Two examples are worked out in some detail: nonresonant Raman scattering and photoluminescence of symmetrical molecules. A discussion of the physical significance of the orientation factors and of their interrelation is given.