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

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