ニュース＆トピックス
セミナーのお知らせ: Adelin Patoux 氏 (Post-doctoral researcher, Universite Cote d’Azur, CNRS)
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日時：2024年9月25日（水）10:30～12:00
場所：東京大学理学部1号館3階340号室 および ZOOM（どちらも事前登録制）
講演者： Adelin Patoux 氏
(Post-doctoral researcher, Universite Cote d’Azur, CNRS)
講演題目: Optimized design strategy of achromatic metasurfaces considering their fundamental dispersion limits
Abstract
Metasurfaces are planar optical components made of structures arranged on a periodic grid smaller than the operating wavelengths. By locally tuning the geometrical parameters of the structures (e.g., the diameter of the nanodiscs), it becomes possible to control the light-matter interaction. This enables, for example, local modulation of the wavefront and the design of extra-thin lenses, known as metalenses.
Such metasurfaces are ideally suited to monochromatic operation, where the only requirement is to find geometries capable of inducing a phase shift ranging from 0 to 2π. A monochromatic metasurface is thus only composed of a dozen or fewer unique geometries.
One of the main challenges facing metasurfaces is the case of achromatic components for large bandwidths (i.e., visible). Here, in order to achieve the same optical functionality across the entire bandwidth, the optical path must remain constant. The phase shift that must be induced for each wavelength then varies as a linear function with frequency, known as dispersion. This considerably increases the difficulties of design, and in particular implies a much higher number of different geometries, since dispersion must now be taken into account instead of a single phase [1].
In this presentation, after an introduction to monochromatic metasurfaces and their design, we'll look in detail at the achromatic problem and how, in fact, the thinness of metasurfaces creates a fundamental limit on achievable dispersion [2,3]. Taking the design of a metalens in the visible as an example, we will present how to identify this limit, and how we can optimize the bandwidth and wavefront amplitude for which this metalens can be considered achromatic.
[1] Shrestha, S., Overvig, A.C., Lu, M. et al. Broadband achromatic dielectric metalenses. Light Sci Appl 7, 85 (2018).
[2] Engelberg, J. and Levy, U., Achromatic flat lens performance limits, Optica 8, 834-845 (2021).
[3] Presutti, F. and Monticone,F., Focusing on bandwidth: achromatic metalens limits, Optica 7, 624-631 (2020).
使用言語：English/英語
紹介教員：小西 邦昭
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