Title:Nonperturbative regime in optical nonlinearities,large and small, fast and slow
Speaker: Prof. Jacob Khurgin
Time: March 12, 14:30
Venue:Room 213, Lecture Hall, Building 18, School of Physics and Optoelectronics
[Abstract]
Recent progress in nanophotonics allows extremely high optical fields to be confined inside resonant structures, whether they are micro resonators, metasurfaces, or plasmonic features.This advancement holds particular significance in nonlinear optics,where traditional perturbative approaches fall short in adequately describing the behavior of optical permittivity (and refractive index) as optical intensities increase.Specifically,deviations from the expected behavior governed by the constant nonlinear index n2 have been noted in transparent conductive oxides operating in the epsilon-near-zero (ENZ) regime [1,2].Various models have been proposed to elucidate this phenomenon, including higher order nonlinear susceptibilities,yet a comprehensive unified theory applicable to diverse physical mechanisms of nonlinearity remains elusive.
In this presentation,I will describe the newly formulated generalized theory of nonlinear permittivity change, which is applicable across various mechanisms, such as simple absorption saturation, ultra-fast nonlinearity (both positive, based on virtual multiphoton processes, and negative, based on the AC Stark effect),thermal effects, or hot-carrier related phenomena as observed in transparent conductive oxides and plasmonic materials. A notable aspect of our theory is that the nonlinear refractive index, regardless of the underlying mechanism, can be adequately described by a simple saturation model, with the saturation field varying for different mechanisms.While a perturbative treatment utilizing higher order susceptibilities suffices for ultrafast nonlinearities, it lacksphysical meaning for other types of nonlinearities, as it does not correspond to the hyperpolarizabilities of electronic wavefunctions. The saturation-like behavior adheres to the adage, 'If something cannot go on forever, it will stop.'麻豆传媒 findings indicate that a straightforward saturation-like description is satisfactory for modeling nonlinearities in most conceivable applications.
Announced by School of Physics and Optoelectronics
