报告题目： Nonperturbative regimein optical nonlinearities, large and small, fast and slow
报告人：Jacob Khurgin（约翰霍普金斯大学教授）
报告时间：2025年3月12日（星期三）下午14:30—16:00
报告地点：物理与光电学院18号楼213报告厅
主办单位：物理与光电学院
报告人简介：
Jacob Khurgin, a professor of electrical and computerengineering at Johns Hopkins University, is known for his diverse and eclecticresearch in the areas of optics, electronics, condensed matter physics, andtelecommunications. He has published eight book chapters, 40 patents, 340papers in refereed journals. He is a member of the American Physical SocietyJoint Council on Quantum Electronics and has served as a technical programcommittee member for more than 60 academic conferences. He has held visitingprofessorships at numerous institutions, including Princeton, UCLA, Brown, ETHin Zurich, and Ecole Normale Superieure in Paris. He was named a Fellow by theAmerican Physical Society and the Optical Society of America.
报告摘要：
Recent progress in nanophotonics allows extremely highoptical fields to be confined inside resonant structures, whether they aremicro resonators, metasurfaces, or plasmonic features. This advancement holdsparticular significance in nonlinear optics, where traditional perturbativeapproaches fall short in adequately describing the behavior of opticalpermittivity (and refractive index) as optical intensities increase.Specifically, deviations from the expected behavior governed by the constantnonlinear index n2 have been noted in transparent conductive oxides operatingin the epsilon-near-zero (ENZ) regime [1,2]. Various models have been proposedto elucidate this phenomenon, including higher order nonlinearsusceptibilities, yet a comprehensive unified theory applicable to diversephysical mechanisms of nonlinearity remains elusive.
In thispresentation, I will describe the newly formulated generalized theory ofnonlinear 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 Starkeffect), thermal effects, or hot-carrier related phenomena as observed intransparent conductive oxides and plasmonic materials. A notable aspect of ourtheory is that the nonlinear refractive index, regardless of the underlyingmechanism, can be adequately described by a simple saturation model, with thesaturation field varying for different mechanisms. While a perturbativetreatment utilizing higher order susceptibilities suffices for ultrafast nonlinearities,it lacksphysical meaning for other types of nonlinearities, as it does notcorrespond to the hyperpolarizabilities of electronic wavefunctions. Thesaturation-like behavior adheres to the adage, 'If something cannot go onforever, it will stop.' Our findings indicate that a straightforwardsaturation-like description is satisfactory for modeling nonlinearities in mostconceivable applications.
