arXiv subjects

Bogdan Borodin

Publications and source records attributed to Bogdan Borodin.

4 recordsLinked to original sources

arXiv2026

Probing Azimuthal Anatomy of Hyperbolic Whispering Gallery Modes in hBN

Scattering-type scanning near-field optical microscopy (s-SNOM) is a powerful tool for investigating polaritonic modes. However, an inherent limitation of this technique is that excitation and detection occur at the same location. This constraint makes it challenging to resolve excitations with complex spatial structures, which can exhibit delicate dependence on the in-coupling conditions. Here, we present a strategy to overcome this limitation by introducing an auxiliary cavity, which serves as a stationary near-field excitation source. This configuration allows the s-SNOM tip to act solely as a detector, and decouples excitation from detection. We apply this approach to whispering gallery modes (WGMs) of hyperbolic phonon-polaritons in hexagonal boron nitride resonators. Through spatially resolved near-field maps we directly observe subwavelength polaritonic WGMs with large and discrete azimuthal momentum ($k_ϕ/ k_0$ up to 15). This allows us to map the frequency and angular behavior of the modes. Notably, we observe dynamic tuning of the effective refractive index by the WGMs to preserve consistent azimuthal momentum $k_ϕ$ under varying excitation conditions. Numerical simulations support the experimental observations and confirm the observation of hyperbolic WGMs. This approach enables direct visualization of previously hidden mode structures in hyperbolic cavities and opens new pathways for momentum-controlled polaritonic device engineering.

cond-mat.mes-hall↗

arXiv2025

Launching Focused and Spatially Confined Phonon-Polaritons in Hexagonal Boron Nitride

Phonon-polaritons offer significant opportunities for low-loss, subdiffractional light guiding at the nanoscale. Despite extensive efforts to enhance control in polaritonic media, focused and spatially confined phonon-polariton waves have only been realized in in-plane-anisotropic crystals (e.g., MoO$_3$) and remain elusive in in-plane-isotropic materials (e.g., hexagonal boron nitride, hBN). In this study, we introduce a novel approach to launching phonon-polaritons by leveraging hBN subwavelength cavities at the Au/SiO$_2$ interface, enabling efficient coupling of cavities to the far-field component of mid-infrared light. Utilizing standard lithographic techniques, we fabricated subwavelength cavities of various shapes and sizes, demonstrating strong field enhancement, resonant mode localization, and generation of propagating phonon-polaritons with well-defined spatial structure. The cavity geometry governs wavefront curvature, spatial confinement, and polariton focusing, providing control over their propagation and achieving record-high in-plane confinement up to $λ/70$. Scattering-type scanning near-field optical microscopy reveals the real-space optical contrast of these cavity-launched modes, allowing for detailed characterization. We believe that our cavity-based approach to phonon-polariton focusing in isotropic media will pave the way for advanced nanophotonic applications.

cond-mat.mes-hall↗

arXiv2025

Mie-resonant silicon waveguide for efficient coupling with excitonic emitters in InSe

Enhancement of radiative coupling efficiency between out-of-plane excitonic emitters in an indium selenide (InSe) film and an integrated waveguide formed by silicon (Si) Mie-resonant nanodisks is experimentally studied. Photoluminescence power at the resonant waveguide output is increased by~2.5 times at 950~nm in comparison with the case of a conventional rib waveguide of the same geometrical parameters due to the efficient excitation of Mie-type magnetic dipole resonances in individual nanoparticles. These results show inspiring possibilities for creating new on-chip light emitters for various integrated photonics applications.

physics.optics↗

arXiv2024

Formation of Thin GaAs Buffer Layers on Silicon for Light-Emitting Devices

This paper presents the experimental results on research of growth processes of GaAs layers on silicon substrates by molecular beam epitaxy. The formation of buffer Si layer in a single growth process has been found to significantly improve the crystalline quality of the GaAs layers formed on its surface, as well as to prevent the formation of anti-phase domains both on offcutted towards the [110] direction and on singular Si(100) substrates. It has been demonstrated that the use of cyclic thermal annealing at temperatures 350-660°C in the flow of arsenic atoms makes it possible to reduce the number of threading dislocations and increase the smoothness of the GaAs layers surface. At the same time, the article considers possible mechanisms that lead to an improvement in the quality of the surface layers of GaAs. It is shown that the thus obtained GaAs layers of submicron thickness on the singular Si(100) substrates have a mean square value of surface roughness 1.9 nm. The principal possibility of using thin GaAs layers on silicon as templates for forming on them light-emitting semiconductor heterostructures with active area based on self-organizing InAs quantum dots and InGaAs quantum well is presented. They are shown to exhibit photoluminescence at 1.2 um at room temperature.

physics.app-ph↗