New Insights into Light Scattering.

Abstract

Laguerre-Gauss (LG) beams change attributes of light-matter interactions due to their possession of well-defined orbital angular momentum (OAM). This dissertation treats the scattering of LG beams from matter in two limits. First, I calculate an effective inelastic scattering transition probability when a LG beam excites a resonant transition. Using this effective transition probability I predict changes in the resonance Raman scattering from the totally symmetric vibrations of molecules due to an incident LG beam. Changes include new overtone peaks and interference effects in resonance Raman spectra of molecules. These predictions are tested with the condense phase spontaneous, resonance Raman scattering of diatomic iodine and iron (III) tetraphenylporphyrin chloride. These tests did not detect the predicted effects.

Second, I investigate the classical electromagnetic scattering of circularly polarized LG beams from metal spheres. I show that the incident OAM density of a LG beam is conserved in the scattering process. In the limit of small particles, the conservation of angular momentum results in an induced transparency. This result could be used for optical information processing by defining an OAM-dependent transfer function.

Also, the conservation of angular momentum amends the plasmonic response of a metallic nano-sphere. Based on the connection between the frequency-dependent scattering and the angular momentum states of surface plasmon modes, a mechanism for control is proposed. This mechanism takes advantage of interference between dominant and weak surface modes to selectively tailor the scattering spectra of plasmonic nano-spheres.

In the course of the investigations during this dissertation, interesting photo-physics and photo-chemistry of a model biological system were uncovered. The dissertation shows that ultrafast transient dynamics of iron (III) tetraphenylporphyrin chloride differ from those of biological heme proteins. Also, in the presence of toluene at low temperatures, resonance Raman scattering shows that spin transitions occur in the photochemistry of the excited electronic states of iron (III) tetraphenylporphyrin. These transitions may prove useful in opto-magnetic functional materials.