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.

Generalized 4 × 4 matrix formalism for light propagation in anisotropic stratified media: study of surface phonon polaritons in polar dielectric heterostructures

“…Here, the highly dispersive and often strongly anisotropic behavior of the dielectric function precludes the use of formalisms that are restricted to special cases. However, it is exactly in these materials and atomic-scale heterostructures thereof [23][24][25][26] , that SPhPs have very recently been demonstrated to enable many novel phenomena such as hyperbolic superlensing 27,28 and negative refraction 29,30 . For instance, hexagonal boron nitride as one of the key components of van der Waals heterostructures 31 , displays many interesting nanophotonic properties due to its naturally hyperbolic character 23,28,30,32,33 .…”

“…However, it is exactly in these materials and atomic-scale heterostructures thereof [23][24][25][26] , that SPhPs have very recently been demonstrated to enable many novel phenomena such as hyperbolic superlensing 27,28 and negative refraction 29,30 . For instance, hexagonal boron nitride as one of the key components of van der Waals heterostructures 31 , displays many interesting nanophotonic properties due to its naturally hyperbolic character 23,28,30,32,33 . Therefore, a most general, robust, and easily implementable numera) Fritz-Haber-Institut der Max-Planck-Gesellschaft, Faradayweg 4-6,14195 Berlin, Germany; Electronic mail: passler@fhi-berlin.mpg.de b) Fritz-Haber-Institut der Max-Planck-Gesellschaft, Faradayweg 4-6,14195 Berlin, Germany ical formalism to analyze the optical response in arbitrarily anisotropic multilayer heterostructures is highly desirable.…”

Graphene-plasmon polaritons: From fundamental properties to potential applications

“…Both papers provide real-space imaging of GPPs with extremely high spatial resolution (∼20 nm) limited only by the dimensions of the AFM probe. s-SNOM has been intensively used, e.g., for exploration of plasmons in graphene Moiré superlattices [63], for observation of ultraslow hyperbolic polariton propagation [64], and for observation of hyperbolic phonon-polaritons in boron nitride [65]. More recently, Alonso-González et al [66] utilized an immovable metal gold rod standing on a graphene sheet as another kind of antenna.…”

Isotopic effects on phonon anharmonicity in layered van der Waals crystals: Isotopically pure hexagonal boron nitride

“…2D layered materials are host to a wide range of polaritonic modes that can be tailored by taking advantage of the intrinsic anisotropy of the materials and their vastly different physical properties [2]. In particular, h-BN has emerged as a promising natural hyperbolic material capable of supporting phonon-polaritons for applications in hyperlensing and subdiffractional resonators [3].…”