title: High-fidelity spherical cholesteric liquid crystal Bragg reflectors generating unclonable patterns for secure authentication.
abstract: Monodisperse cholesteric liquid crystal microspheres exhibit spherically symmetric Bragg reflection, generating, via photonic cross communication, dynamically tuneable multi-coloured patterns. These patterns, uniquely defined by the particular sphere arrangement, could render cholesteric microspheres very useful in countless security applications, as tags to identify and authenticate their carriers, mainly physical objects or persons. However, the optical quality of the cholesteric droplets studied so far is unsatisfactory, especially after polymerisation, a step required for obtaining durable samples that can be used for object identification. We show that a transition from droplets to shells solves all key problems, giving rise to sharp patterns and excellent optical quality even after polymerisation, the polymerised shells sustaining considerable mechanical deformation. Moreover, we demonstrate that, counter to prior expectation, cross communication takes place even between non-identical shells. This opens additional communication channels that add significantly to the complexity and unique character of the generated patterns.
authors.affiliation: University of Luxembourg, Physics &Materials Science Research Unit, L-1511 Luxembourg, Luxembourg.
authors.forename: Yong
authors.initials: Y
authors.lastname: Geng
authors.affiliation: University of Luxembourg, Physics &Materials Science Research Unit, L-1511 Luxembourg, Luxembourg.
authors.forename: JungHyun
authors.initials: J
authors.lastname: Noh
authors.affiliation: University of Ljubljana, Faculty of Mathematics and Physics, Jadranska 19, SI 1000 Ljubljana, Slovenia.|J. Stefan Institute, Jamova 39, SI 1000 Ljubljana, Slovenia.
authors.forename: Irena
authors.initials: I
authors.lastname: Drevensek-Olenik
authors.affiliation: Faculty of Physics, University of Vienna, A-1090 Vienna, Austria.
authors.forename: Romano
authors.initials: R
authors.lastname: Rupp
authors.affiliation: University of Luxembourg, Interdisciplinary Center for Security and Trust, L-2721 Luxembourg, Luxembourg.
authors.forename: Gabriele
authors.initials: G
authors.lastname: Lenzini
authors.affiliation: University of Luxembourg, Physics &Materials Science Research Unit, L-1511 Luxembourg, Luxembourg.
authors.forename: Jan P F
authors.initials: JP
authors.lastname: Lagerwall