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arXiv · 2608.27733

Deterministic control over launching efficiency of higher-order hyperbolic phonon polaritons

Thiago S. Arnaud·John E. Buchner·Ryan W. Spangler·Maximilian Obst·Jon-Paul Maria·Joshua D. Caldwell
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Abstract

Hyperbolic materials, which exhibit an extreme form of birefringence enabling the volume confinement and frequency-dependent propagation of deeply sub-diffractional optical modes, offer the opportunity for extreme confinement via the stimulation polaritonic modes, with substantially higher confinement obtained through the efficient excitation of of the higher-order (shorter wavelength) hyperbolic polaritonic modes, which they can support. However, while these higher-order hyperbolic polaritons (HO-HPhPs) form high-momentum ray-like propagation within the bulk, efficient excitation of these modes, especially in contrast to the long-wavelength lower-momentum surface polariton propagating modes, has remained a challenge. Critically, the large momentum mismatch between these modes and free-space light, alongside the spatial mismatch between the sub-diffractional scatterer and the distinct modal distribution of HO-HPhPs, lead to a suppressed launching efficiency of these higher-order modes, limiting their use in nanophotonic applications. Here, we report the experimental observation of a 10-fold enhancement in the excitation efficiency of HO-HPhPs through the use of subsurface scatterers over traditional surface scattering (e.g. a flake edge or gold launcher) within single-crystalline {\alpha}-MoO3 slabs. We employ full-wave numerical simulations to investigate the role of the spatial overlap between HO-HPhP modal distributions and the scatterer placement upon excitation efficiency. Furthermore, we develop a generalized process using transfer matrix method to selectively design modal HO-HPhP excitation, which advances the capabilities of HPhP multiplexing for on-chip applications.

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Thiago S. Arnaud, John E. Buchner, Ryan W. Spangler, Maximilian Obst, Jon-Paul Maria, Joshua D. Caldwell. 2026-08-27. Deterministic control over launching efficiency of higher-order hyperbolic phonon polaritons. https://arxiv.org/abs/2608.27733

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