By taking ordinary materials and rearranging them into complex shapes on the same scale as the wavelength of light, it is well known that one can drastically enhance the interactions between light and matter, from resonant absorption to surface-enhanced Raman scattering. In this talk, we will present a recent theoretical technique that reveals upper limits to such enhancement for a given material, regardless of the geometric shape. These theoretical bounds provide guidance to the engineering design of new devices, whether by intuitive hand designs or massive computational geometry optimization.  In some cases, we find that simple known structures are nearly optimal, but in other cases (such as Raman sensing) there appears to be enormous room for improvement attainable by new geometries.  Moreover, the upper limits derive from remarkably simple principles — energy conservation and the optical theorem — that allow them to be generalized to a wide range of phenomena. Already, we have found new upper limits to absorption, scattering, spontaneous emission, thermal radiation, Cherenkov radiation, and Raman scattering, as well as figures of merit allowing rapid comparison of materials over different bandwidths.

报告人简介：

Steven G. Johnson is a Professor of Applied Mathematics and Physics at MIT, where he joined the faculty in 2004 and previously received a PhD in physics (2001) and BS degrees in physics, mathematics, and computer science (1995).  His research centers on wave–matter interactions and electromagnetism in media structured on the wavelength scale (“nanophotonics”), especially in the infrared and optical regimes—where he works on many aspects of the theory, design, and computational modeling of nanophotonic devices, both classical and quantum. He is coauthor of over 200 papers and over 30 patents in this area, including the textbook Photonic Crystals: Molding the Flow of Light. Professor Johnson also has a long history of contributions to scientific computation and software, including the MPB and Meep electromagnetic simulation tools (cited in over 1000 papers to date) and the FFTW fast Fourier transform library (for which he received the 1999 J. H. Wilkinson Prize for Numerical Software).