Menabde, Sergey G. Jahng, Junghoon Boroviks, Sergejs Ahn, Jongtae Heiden, Jacob T. Hwang, Do Kyung Lee, Eun Sung Mortensen, N. Asger Jang, Min Seok 2024-01-19T11:00:51Z 2024-01-19T11:00:51Z 2022-09-15 2022-11 https://pubs.kist.re.kr/handle/201004/114428 Orthorhombic molybdenum trioxide (α-MoO3), a newly discovered polaritonic van der Waals crystal, is attracting significant attention due to its strongly anisotropic mid-infrared phonon-polaritons. At the same time, coupling of polariton with its mirror image in an adjacent metal gives rise to a significantly more confined image mode. Here, monocrystalline gold flakes—an atomically flat low-loss substrate for mid-infrared image polaritons—are employed to measure the full complex-valued propagation constant of the hyperbolic image phonon-polaritons in α-MoO3 by near-field probing. The anisotropic dispersion is mapped and the damping of the polaritons propagating at different angles to the crystallographic directions of α-MoO3 is analyzed. These experiments demonstrate the strongly confined image phonon-polaritons in α-MoO3 exhibiting intrinsic limiting lifetime of 4.2 ps and a propagation length of 4.5 times the polariton wavelength, owing to the negligible substrate-mediated loss. Furthermore, it is shown that the image modes with positive group velocity have simultaneously larger momentum and lifetime compared to their counterparts on a dielectric substrate, while the image modes with negative group velocity possess a smaller momentum. These results spotlight the hyperbolic image phonon-polaritons as a superior platform for unconventional light manipulation at the nanoscale. English John Wiley and Sons Inc. Low-Loss Anisotropic Image Polaritons in van der Waals Crystal alpha-MoO3 Article 10.1002/adom.202201492 1 Advanced Optical Materials, v.10, no.21 Advanced Optical Materials 10 21 N scie scopus 000850307100001 Materials Science, Multidisciplinary Optics Materials Science Optics Article; Early Access van der Waals crystals phonon-polaritons image polaritons