主题：Optimizing the Nonlinear Optical Response of Plasmonic Metasurfaces
主持人：李辉 副研究员
时间：2018.5.14 上午10:00
地点：理科大楼A508
Prof. Prior was educated in Jerusalem, Berkeley and Harvard before joining the Weizmann Institute of Science in 1979. Since then, with the exception of sabbatical visits to Bell Communications Research Laboratories in the U.S. and the École Normale Supérieure in Paris, he has been a member of the Institute’s Department of Chemical Physics. Prof. Prior chaired the department, headed the Institute’s Division of Information Systems, chaired the Institute’s Scientific Council of all tenured professors, and until recently has served as Dean of the Faculty of Chemistry. Prof. Prior works in the fields of light matter interaction, laser spectroscopy and laser material processing. His research ranges from developing methods in nonlinear optical spectroscopy and Four Wave Mixing, to nanotechnology and surface modification on the nanoscale. In recent years, the main focus of his work is in Plasmonics and meta-surfaces, designing and fabricating intelligent nano-structures for enhanced nonlinear optical response
报告内容简介：
Raman or wave mixing processes have been traditionally studied in gas-phase molecules where one tunes the laser frequencies to the molecular energy levels for resonance enhancements. With metasurfaces one can do the reverse, namely for fixed laser frequencies the ‘system’ is tuned to be resonant with the laser frequencies. The resonant local field enhancements in such systems, typically connected to surface plasmons, enable the design of nanoscale nonlinear optical components, which, in turn, can be integrated into novel nanophotonic devices.
The standard way to optimize the nonlinear response is to design the material linear spectrum to be resonant with the relevant frequencies of the nonlinear process, because high far-field transmission at a certain frequency suggests large local field enhancements caused by surface plasmons. Recently we demonstrated the enhancement of Four-Wave Mixing (FWM) by tuning the response of a nanohole array to have a plasmonic resonance at the pump and stokes input frequencies[1].
Here we show that while the intuitive linear optimization may identify structures with high nonlinear response, there is a different approach that provides nonintuitive optimized structures with even higher nonlinear response. We use the evolutionary Genetic Algorithms (GA) for optimization based on two target functions: the (conventional) product of the linear Extra Ordinary Transmission at the relevant frequencies anddirect NL calculation of the FWM signal (New). We derive optimized structures [2], measure them and discuss the counter intuitive linear spectra (blue spectra, with only two linear resonant enhancements) of the directly optimized FWEM response.
References
[1] Almeida, E. & Prior, Y. Rational design of metallic nanocavities for resonantly enhanced FWM, Sci. Rep. 5, 10033 (2015).
[2] Blechman Yael, Almeida Euclides, Sain Basudeb and Yehiam Prior, to be published (2018)