Using sum rules to guide experiential and theoretical studies of the intrinsic nonlinear-optical susceptibility of organic molecules

This dissertation combines theoretical and experimental studies of organic moleculesto understand light-matter interactions with the goal of making more efficient nonlinearoptical molecules. We use a finite element method to numerically calculate and optimize the nonlinear-optical susceptibilities of 1-dimensional molecules, which resulted in a new paradigm for fabricating molecules with better nonlinear properties. This approach was used as a guide by researchers to identify and characterize a record-high intrinsic hyperpolarizability. Using the results of a sum rule analysis, we propose a new method for modeling the nonlinear-optical spectra of molecules. We apply our theory to the two-photon absorption cross section of the Air Force dye called AF455, and find that it is consistent with our measurements. The properties of the first two excited states of AF455 determined with a combination of linear absorption spectroscopy and hyper-Rayleigh scattering measurements are sufficient to predict, within experimental uncertainty, the full two-photon absorption spectrum

Experimental verification of a self-consistent theory of the first-, second-, and third-order (non)linear optical response

We show that a combination of linear absorption spectroscopy, hyper-Rayleigh scattering, and a theoretical analysis using sum rules to reduce the size of the parameter space leads to a prediction of the two-photon absorption cross-section of the dye AF455 that agrees with two-photon absorption spectroscopy. Our procedure, which demands self-consistency between several measurement techniques and does not use adjustable parameters, provides a means for determining transition moments between the dominant excited states based strictly on experimental characterization. This is made possible by our new approach that uses sum rules and molecular symmetry to rigorously reduce the number of required physical quantities.Comment: 10 pages, 9 figure

Studies on optimizing potential energy functions for maximal intrinsic hyperpolarizability

We use numerical optimization to study the properties of (1) the class of one-dimensional potential energy functions and (2) systems of point charges in two-dimensions that yield the largest hyperpolarizabilities, which we find to be within 30% of the fundamental limit. We investigate the character of the potential energy functions and resulting wavefunctions and find that a broad range of potentials yield the same intrinsic hyperpolarizability ceiling of 0.709.Comment: 9 pages, 9 figure

Two-photon fluorescence measurements of reversible photodegradation in a dye-doped polymer

Y. Zhu, J. Zhou, and M. G. Kuzyk, " Two-photon fluorescence measurements of reversible photodegradation in a dye-doped polymer," Opt. Lett. 32, 958-960 (2007) We report on the dynamics of photodegradation and subsequent recovery of two-photon fluorescence in a dye-doped polymer. The energy dependence suggests that photo-degradation is a linear process while recovery is entropic. Such recovery could be useful to high-intensity devices such as two-photon absorbers, which can be used in many applications

Pushing the hyperpolarizability to the limit

Opt. Lett. 31, 2891-2893(2006) We use numerical optimization to find a one-dimensional potential energy function that yields the largest hyperpolarizability, which we find is within 30% of the fundamental limit. Our results reveal insights into the character of the potential energy functions and wavefunctions that lead to the largest hyperpolarizability. We suggest that donor-acceptor molecules with a conjugated bridge with many sites of reduced conjugation to impart conjugation modulation may be the best paradigm for making materials with huge hyperpolarizabilities that approach the fundamental limit