Kate Rodriquez PhD Defense: Multipolar Raman Scattering on Plasmons

Thursday, March 7, 2019 - 11:00
1201 Natural Sciences II, University of California, Irvine
Kate Rodriquez
Event Title: 
Apkarian Group NEWS! Kate Rodriquez PhD Defense - THURS March 7, 2019
Kate Rodriquez
Thursday, March 7, 2019 - 11:00am

Abstract: Dichroism in Raman has long been an area of interest in spectroscopy as a powerful tool for elucidating molecular chirality. Here, I will provide details from investigations into plasmonic, rather than molecular, dichroism observed in surface-enhanced Raman spectroscopy (SERS) studies. The sample used is the prototypical dimer nantenna, consisting of two gold nanospheres, which is functionalized with bipyridyl ethylene molecular reporters. Experiments in linear dichroism (LD) reveal that the structures scatter as multipolar antenna, with the molecular vibrational Raman lines following the polarization pattern of the dimer on which they reside. Investigations into circular dichroism (CD) of the dimers reveal giant CD with handedness that depends on the orientation of the dimer in the plane perpendicular to excitation. We attribute this counter intuitive effect to the multipolar response of the plasmonic antenna, which arises from its large size with respect to the excitation wavelength. Here, the long-wave approximation breaks down and expansion of the light-matter interaction to the first order in spatial dispersion leads to magnetic dipole and electric quadrupole Raman scattering comparable to the zeroth-order electric dipole exclusively considered in standard Raman. The observed LD and CD, including orientation-dependent handedness, find resolution in the framework of Jones calculus. I will present these findings and connect them broadly to considerations such as time reversal symmetry, chiral connectedness, and bi-isotropic media. yes