Studies aimed at understanding the global properties of the hyperpolarizabilities have focused on identifying universal properties when the hyperpolarizabilities are at the fundamental limit. These studies have taken two complimentary approaches: (1) Monte Carlo techniques that statistically probe the full parameter space of the Schrödinger equation using the sum rules as a constraint, and (2) numerical optimization studies of the first and second hyperpolarizability where models of the scalar and vector potentials are parameterized and the optimized parameters determined, from which universal properties are investigated. Here, we employ an energy spectrum constraint on the Monte Carlo method to bridge the divide between these two approaches. The results suggest an explanation for the origin of the factor of the 20–30 gap between the best molecules and the fundamental limits and establish the basis for the three-level ansatz.
© 2011 Optical Society of America
Atomic and Molecular Physics
Original Manuscript: January 5, 2011
Manuscript Accepted: February 7, 2011
Published: March 23, 2011
Shoresh Shafei and Mark G. Kuzyk, "Critical role of the energy spectrum in determining the nonlinear-optical response of a quantum system," J. Opt. Soc. Am. B 28, 882-891 (2011)