title: Hyperbolic phonon-polaritons in boron nitride for near-field optical imaging and focusing.
abstract: Hyperbolic materials exhibit sub-diffractional, highly directional, volume-confined polariton modes. Here we report that hyperbolic phonon polaritons allow for a flat slab of hexagonal boron nitride to enable exciting near-field optical applications, including unusual imaging phenomenon (such as an enlarged reconstruction of investigated objects) and sub-diffractional focusing. Both the enlarged imaging and the super-resolution focusing are explained based on the volume-confined, wavelength dependent propagation angle of hyperbolic phonon polaritons. With advanced infrared nanoimaging techniques and state-of-art mid-infrared laser sources, we have succeeded in demonstrating and visualizing these unexpected phenomena in both Type I and Type II hyperbolic conditions, with both occurring naturally within hexagonal boron nitride. These efforts have provided a full and intuitive physical picture for the understanding of the role of hyperbolic phonon polaritons in near-field optical imaging, guiding, and focusing applications.
authors.affiliation: Institute of Physics (IA), RWTH Aachen University, Aachen 52056, Germany.
authors.forename: Peining
authors.initials: P
authors.lastname: Li
authors.affiliation: 1] Institute of Physics (IA), RWTH Aachen University, Aachen 52056, Germany [2] Fraunhofer Institute for Laser Technology ILT, Aachen 52074, Germany.
authors.forename: Martin
authors.initials: M
authors.lastname: Lewin
authors.affiliation: School of Physics and Astronomy, University of Manchester, Oxford Road, Manchester M13 9PL, UK.
authors.forename: Andrey V
authors.initials: AV
authors.lastname: Kretinin
authors.affiliation: US Naval Research Laboratory, 4555 Overlook Avenue, S.W., Washington, D.C. 20375, USA.
authors.forename: Joshua D
authors.initials: JD
authors.lastname: Caldwell
authors.affiliation: School of Physics and Astronomy, University of Manchester, Oxford Road, Manchester M13 9PL, UK.
authors.forename: Kostya S
authors.initials: KS
authors.lastname: Novoselov
authors.affiliation: National Institute for Materials Science, 1-1 Namiki, Tsukuba, Ibaraki 305-0044, Japan.
authors.forename: Takashi
authors.initials: T
authors.lastname: Taniguchi
authors.affiliation: National Institute for Materials Science, 1-1 Namiki, Tsukuba, Ibaraki 305-0044, Japan.
authors.forename: Kenji
authors.initials: K
authors.lastname: Watanabe
authors.affiliation: Fraunhofer Institute for Laser Technology ILT, Aachen 52074, Germany.
authors.forename: Fabian
authors.initials: F
authors.lastname: Gaussmann
authors.affiliation: 1] Institute of Physics (IA), RWTH Aachen University, Aachen 52056, Germany [2] Fraunhofer Institute for Laser Technology ILT, Aachen 52074, Germany.
authors.forename: Thomas
authors.initials: T
authors.lastname: Taubner