Metasurfaces with Maximum Chirality Empowered by Bound States in the Continuum | Dr. Maxim Gorkunov

Optical Seminar at The Department of Physics & Engineering, ITMO | 13 Nov 2020 Timecodes are below the abstract. Dr. Maxim Gorkunov, Department of Theoretical Studies, Shubnikov Institute of Crystallography, Federal Scientific Research Centre “Crystallography and photonics”, Russian Academy of Sciences Title: "Metasurfaces with Maximum Chirality Empowered by Bound States in the Continuum" Abstract: Over the past years, it has been repeatedly demonstrated that chiral metasurfaces – planar arrays of subwavelength elements of broken mirror symmetry – are capable of unprecedentedly high optical chirality. While zero chirality is attributed to achiral objects which equally strongly interact with light of both circular polarizations, the maximum chirality is assigned to those that are uncoupled from one circular polarization and extremely strongly interact with the opposite one. We demonstrate how precise shaping of the coupling of metasurface quasi bound states in the continuum (BICs) to free-space waves can empower and maximize the optical chirality. Based on the phenomenological coupled-mode theory, we elucidate the general properties of the maximum chiral BIC resonances that manifest themselves as narrow peaks of unit height in the circular dichroism spectrum. A particular realization of maximum chiral BIC metasurface can be based on rotationally symmetric arrays of pairs of dielectric bars. We present a step-by-step design, starting from arrays with fully uncoupled BICs and carefully enabling their chiral selective coupling by symmetry breaking perturbations. 0:00:00 - Intro 01:18 - start of the talk by Dr. Maxim Gorkunov 02:00 - what is Shubnikov institute of crystallography 02:40 - sound problems 04:24 - Outline of the talk 05:34 - Intro natural and artificial optical chirality 12:36 - question from the chat by Dr. Maxim Gorlach on hyperbolic sine and cosine functions 16:58 - Chiral Nanostrucutres 23:39 - S-matrix method 28:30 - question by Dr. Maxim Gorlach 32:25 - Phenomenology of Resonances with Coupled-mode Theory (CMT) 41:30 - Maximizing Chirality 44:33 - BIC for Chirality 47:20 - comment from the chat by Kristina Frizyuk on typos/mistakes in Wigner and von Neumann original paper on BIC 52:56 - BIC to quasi-BIC 56:00 - BIC to chiral quasi-BIC 58:26 - question by Dr. Anton Samusev 1:02:05 - remark from Dr. Andrey Bogdanov 1:03:05 - BIC with rotation The Department of Physics and Engineering of ITMO University (Saint Petersburg, Russia) hosts online weekly seminars to discuss recent scientific achievements of researchers from all over the world with a wide audience. The topics include experimental (Optical seminar) and theoretical (Theoretical seminar) aspects of nanophotonics, solid-state physics, material science, as well as design and applications of radiofrequency structures and devices (Microwave seminar). Upcoming and past events can be found at https://physics.itmo.ru/en/seminars   / physics.itmo     / physics_itmo     / physics.itmo   #OpticalSeminar #ITMO #новыйфизтех #scientificseminar