Two-photon photoselection: an irreducible tensor analysis

The electrochromic effect of a static electric field on the rate of absorption of electromagnetic radiation by a molecular fluid is investigated within the framework of quantum electrodynamics. The anisotropic, Boltzmann-weighted orientation of polar molecules in a fluid is treated using an exact method, giving a set of expressions that include both the optical and electro-optical pathways. Using irreducible tensor methods the complete set of rate equations is presented, and symmetry implications are analysed in detail. Polarisation dependence is also explicitly included in the results, and the likely orders of magnitude of the various rate contributions are estimated.