Plasmonics: Lofty Promise, Harsh Reality, and a Glimmer of Hope
Speaker: Jacob B. Khurgin, Johns Hopkins University
Series: Topical Seminars
Location: Bowen Hall Auditorium
Date/Time: Tuesday, April 26, 2011, 12:30 p.m. - 1:15 p.m.
Recent years have seen staggering growth of interest in using nanostructured metals in optical range with the goal of enhancing linear and nonlinear optical properties or even engineering novel optical properties unknown in Nature â usually this burgeoning field is referred to as âPlasmonics and Metamaterialsâ?. After the initial years of excitement the community is slowly beginning to recognize that loss in the metal is an important factor that might impede practical application of plasmonic devices, be it in signal processing, sensing, imaging or more esoteric applications like cloaking. Yet there is still an optimism that the loss can be either cleverly âdesigned awayâ?, compensated by gain, or a new lossless materials can be found. In this talk we examine these concepts one by one and find that they all have limitations. First we show that when it comes to enhancing the device performance (solar cells, sensors etc.) only the most inefficient devices can be improved by plasmonics while the performance of any decent device will only degrade. Then we demonstrate that in truly sub-wavelength metal structures the metal loss is inherent and cannot be engineered away by clever changes in shape. We then consider the idea of compensating loss using semiconductor gain medium and demonstrate that required gain can never be achieved due to increase in recombination rates caused by Purcell effect. After that we consider the physics of losses in metals at optical frequencies and show that the nature of these losses is quite different from the losses in RF domain. We then show that negative dielectric constant at optical frequencies does not have to inevitably lead to large absorption, and guardedly point to the tentative way in which new materials with negative dielectric constant and very low loss might be synthesized, thus restoring the hope for plasmonics.