《表面等离子体光学:光明的前途、残酷的现实和一丝丝的希望》
Plasmonics:Lofty Promise, Harsh Reality, and a Glimmer of Hope.
报告人:Jacob B Khurgin 约翰霍普金斯大学, 美国
时间:2017年11月22日(周三)14:00~16:00
地点:理学院(10号楼)415室
Recentyears have seen staggering growth of interest in using nanoscalemetal/dielectric structures in optical and near IR ranges with the goal ofenhancing linear and nonlinear optical properties or even engineering noveloptical properties unknown in Nature – usually this burgeoning field isreferred to as “Plasmonics and Metamaterials”. After the initial years ofexcitement the community is slowly beginning to recognize that loss in themetal is an important factor that might impede practical application of plasmonicdevices, be it in signal processing, sensing, imaging or more esotericapplications like cloaking. Yet there is still an optimism that the loss can beeither cleverly “designed away”, compensated by gain, or a new losslessmaterials can be found. In this talk we examine these concepts one by one andfind that they all have limitations. First we show that when it comes toenhancing the device performance (solar cells, sensors etc.) only the mostinefficient devices can be improved by plasmonics while the performance of anydecent device will only degrade. Then we demonstrate that in trulysub-wavelength metal structures the metal loss is inherent and cannot beengineered away by clever changes in shape. We then consider the idea ofcompensating loss using semiconductor gain medium and demonstrate that requiredgain can never be achieved due to increase in recombination rates caused byPurcell effect. After that we consider the physics of losses in metals atoptical frequencies and show that the nature of these losses is quite differentfrom the losses in RF domain. We then show that negative dielectric constant atoptical frequencies does not have to inevitably lead to large absorption, andguardedly point to the tentative way in which new materials with negativedielectric constant and very low loss might be synthesized, thusrestoring the faint hope for plasmonics.