Phase gradient metasurfaces are flat optical structures with potential to manipulate amplitude, phase, and polarization of electromagnetic waves using arrays of subwavelength nanoantennas. Currently most metasurfaces are 'static' and have functions that are fixed at the time of fabrication. By making antenna arrays tunable or reconfigurable in their phase, amplitude, and polarization response through incorporation of electro-optical effects, one can achieve spatiotemporal control of the phase gradient after fabrication. Time modulation can be either be 'quasi-static', where temporal variations are sufficiently slow that they do not change the scattered light frequency, or in a regime where the modulation rate is high enough to generate new frequencies. In this way, time modulation opens a four-dimensional active metasurface design space where control over the spectral content of scattered light, in addition to its spatial features, can extend light manipulation to encompass space-time photonic transitions. New materials are also adding new functions: the excitonic birefringence of the intriguing van der Waals semiconductor black phosphorus has enabled actively tunable spectrally broadband polarization conversion over nearly half the Poincaré sphere. Both linear to circular and cross-polarization conversion with voltage are possible, demonstrating dynamic access to polarization diversity.
Bio: Harry Atwater is the Otis Booth Leadership Chair of the Division of Engineering and Applied Science, and the Howard Hughes Professor of Applied Physics and Materials Science at the California Institute of Technology. Atwater's scientific effort focuses on nanophotonic light-matter interactions. His work spans fundamental nanophotonic phenomena and applications, including active wavefront shaping of light using metasurfaces, optical propulsion, quantum nanophotonics as well as solar energy conversion.
Atwater was an early pioneer in nanophotonics and plasmonics and gave a name to the field of plasmonics in 2001. He is Chair of the LightSail Committee for the Breakthrough Starshot program. Currently Atwater is also the Director for the Liquid Sunlight Alliance (LiSA), a Department of Energy Hub program for solar fuels, and was also the founding Editor in Chief of the journal ACS Photonics. Atwater is a Member of the US National Academy of Engineering, and a Web of Science Highly Cited Researcher.
This seminar is sponsored by the Department of Applied Physics and the Ginzton Laboratory