LISE 303, Noon
Abstract: Recently there have been significant interests in studying the interaction of light with artificially engineered materials. In particular, metasurfaces, which consist of a single layer of nanostructures with subwavelength spacing patterned at an interface, have received much attention as they have the potential to replace traditional refractive-optics with compact, planar devices that can be realized with only a single layer of lithography. Furthermore, these devices can also be designed to possess novel functionalities with little to no increase in fabrication complexity. I will first give an overview of the basic principles behind metasurfaces, and highlight some key works demonstrating their applicability and performance, e.g. high numerical metasurface lenses with diffraction-limited focal spots at visible wavelengths. Next we will discuss some limitations of these metasurfaces in the form of aberrations, particularly chromatic aberrations which arise as a result of dispersion. I will show how these can be mitigated or otherwise exploited through dispersion engineering, leading to achromatic flat lenses over a continuous bandwidth, and an ultra-compact chiral spectrometer. These devices bolster the claims of metasurfaces as being more than objects of academic curiosity and demonstrate their usefulness in a practical setting.
About the Speaker: Alexander Zhu completed his B. Eng. in in Materials Science and Engineering at the University of Pennsylvania (UPenn), and his M. S. at Harvard. At UPenn he worked on various topics related to nanophotonics, such as plasmonics and light-matter interactions in 2D-materials. He is currently pursuing his Ph.D. in Applied Physics under Professor Federico Capasso at Harvard.