HYPERPOLARIZABILITY OF HELICAL POLYMER MOLECULES AND SAMPLING OF IR-ACTIVE OPTICAL PHONON DISPERSION CURVES

The selection rules for the inelastic three-photon scattering of light by helical molecules is obtained from group theoretical analysis. It is shown that the dispersion curve (frequency vs wave vector) for ir-active optical phonons may be sampled at four points throughout the Brillouin zone by measuring the frequency of the scattered light as a function of the polarization of both the incident (laser) and the scattered light provided that proper orientation of the laser light relative to the helix axis is maintained.