Classical model of the upper bounds of the cascading contribution to the second hyperpolarizability

Abstract

We investigate whether microscopic cascading of second-order nonlinearities of two molecules in the side-by-side configuration can lead to a third-order molecular nonlinear-optical response that exceeds the fundamental limit. We find that for large values of the second hyperpolarizability, the side-by-side configuration has a cascading contribution that lowers the direct contribution. However, we do find that there is a cascading contribution to the second hyperpolarizability when there is no direct contribution. Thus, while cascading can never lead to a larger nonlinear-optical response than for a single molecule with the same number of electrons, it may provide design flexibility in making large third-order susceptibility materials when the molecular second hyperpolarizability vanishes.

Modeling off-resonant nonlinear-optical cascading in mesoscopic thin films and guest-host molecular systems

“…(17) and (20)- (25) are first-order corrections to the response of molecules that are polarized along the direction of the applied field. With a more rigorous approach, one can find the effective (hyper)polarizabilities for all possible components.…”

“…Because there are larger cascading enhancements at higher concentration, we consider a hexagonal close-packed structure with a center-of-mass separation distance of approximately 10.04Å. [28] Note that a past study showed that perturbed energy states from cascaded molecules have small effects on large off-resonant nonlinear optical responses, [17] where we only observe significant effects after the molecules have passed into the "forbidden" zone in which they spatially overlap.…”

“…[38,39] A full treatment of the cascading contributions to k (3) for a pair of one-dimensional molecules in an electric field at fixed locations is given in Ref. [17]. For our current example, however, we ignore the azimuthal angle and treat only the average polar angle in an attempt to reduce orientational complexities.…”

“…[5][6][7] Earlier studies focused on a tensor formalism to describe correlated cascading effects in bulk materials, [1] while others focused on cascading between coupled molecules only. [4,8] Mesoscale nonlinear optical effects, however, have not been well investigated, and give new insights into enhancing the nonlinear susceptibility that are not present in a bulk approximation. [9] Here, we use the self-consistent field approach to cascading (Bloembergen's method [10]) to approximate the sum of the dipolar response fields and thereby the cascading contribution in mesoscopic systems.…”

Symmetry analysis of Raman scattering mediated by neighboring molecules

“…A similar type of coupling can be exploited to enhance second order hyperpolarizabilities, in which connection such an interaction is referred to as cascading. 18 Our present results lead to a detailed analysis on the symmetry constraints and selection rules governing the emergence of proximity-induced Raman signals. a) david.andrews@physics.org…”