This is a past event.

Dr. Ahmed Dorrah of Harvard University will be presenting at this week's physics colloquium. Please join the presentation on Thursday, March 24th at 4:00pm via Zoom.

3D Structured Light with Dielectric Metasurfaces

Abstract: Wavefront engineering at the subwavelength has opened new routes in science and technology thanks to metasurfaces, digital holography, and plasmonic devices. In this talk, we discuss ongoing efforts in Structured Light generation with focus on multifunctional flat optics that can perform parallel polarization analysis. These devices mimic the role of several polarizers and waveplates in a compact footprint, thereby shrinking conventional imaging systems and polarimeters. We also present metasurfaces that can structure fundamental properties of light — such as its spin and orbital angular momentum (OAM) — in 3D. After a single interaction with these devices, output light modifies its polarization and OAM at each transverse plane thereafter, as if encountering virtual optics along its path. We show that this evolution in angular momentum is accompanied by a topological phase factor (i.e., Berry phase) which can be engineered on-demand. By introducing a Berry phase gradient along the propagation direction, one can perturb the effective wavevector, leading to spin-dependent shifts in the size (i.e., spatial frequency) of the output beam. We finally discuss some implications of this phenomenon in optics.

Bio:  Dr. Dorrah is a postdoctoral fellow in the School of Engineering and Applied Sciences (SEAS) at Harvard University, working in the areas of Structured Light and Flat Optics. He obtained his MASc (2015) and PhD (2019) degrees, both from the University of Toronto, in Electrical and Computer Engineering. During his PhD, he joined Lawrence Berkeley National Lab (LBL) and the University of the Witwatersrand in South Africa as a visiting research scholar. Dr. Dorrah’s research interest covers the wide area of light-matter interaction, structured light, and flat optics. He is currently developing compact devices which generate structured light for remote sensing, micromanipulation, biological imaging, and optical communications.