arXiv subjects

Denis Kolchanov

Publications and source records attributed to Denis Kolchanov.

3 recordsLinked to original sources

arXiv2026

Optically Transparent Meta-Grating Embedded in Rear Windshields for Automotive Radar Detection

Radar plays a crucial role in automotive safety by enabling reliable object detection, thereby assisting drivers and, prospectively, serving as one of the primary sensors in autonomous driving. The radar visibility of a road participant depends on its radar cross-section (RCS). While RCS is an inherent property, enhancing it, similar to using reflective vests for optical visibility, can significantly improve radar detection through cooperative target design. However, modern vehicles are not designed for this purpose, and embedded reflectors are not utilized due to the industry's conservative approach and the limited space available on the vehicle's exterior. Rear windshields offer a vast unused area, but they must still serve their primary function and remain transparent. We propose utilizing this area by embedding a reflecting surface that accounts for the interrogation scenario geometry and the angular tilt of the rear windshield, ensuring the wave is retroreflected back to the radar. The surface is realized as an array of thin conductive wires with a periodicity that provides in-phase excitation for the design incidence angle. Given that automotive radars operate in the millimeter-wave regime (77-81 GHz), large-scale surfaces with sub-millimeter manufacturing accuracy are required. This is achieved by imprinting conductive inks, composed of silver nanoparticles and binders, into grooves in the glass. The fabricated 10x10 sq. sm. sample, with around 90% optical transparency, demonstrates an RCS of 8 sq. m., surpassing the typical RCS of a car. Extrapolating this performance to the entire rear window with an embedded meta grating, a typical RCS of 1000 sq. m. can be achieved, thereby enhancing the detectability range by nearly an order of magnitude. Smart windows enable advanced applications in wireless communication, such as automotive scenarios, IoT, and many others.

physics.app-ph↗

arXiv2024

Optomechanically and Themo-optically driven Interactions between Gilded Vaterite Nanoparticles in Bubbles

The capability to tailor mutual interactions between colloidal nanoparticles strongly depends on the length scales involved. While electrostatic and optomechanically driven interactions can cover nano and micron-scale landscapes, controlling inter-particle dynamics at larger distances remains a challenge. Small physical and electromagnetic cross-sections of nanoparticles make long-range interactions, screened by a fluid environment, inefficient. To bypass the limitations, we demonstrate that forming micron-scale bubbles around gilded vaterite nanoparticles enables mediating long-range interactions via thermo-optical forces. Femtosecond laser illumination leads to the encapsulation of light-absorbing particles inside long-lasting micron-scale bubbles, which in turn behave as negative lenses refracting incident light. Our experiments reveal the bubble-induced collimation of laser beams, traversing over mm-scale distances. The collimated beams are visualized with the aid of phase-contrast Schlieren imaging, which reveals refractive index variations, caused by temperature gradients within the fluid. We demonstrate that the refracted beams initiate the formation of secondary bubbles around nearby gilded vaterite particles. As the consequence, we demonstrate the ability to control secondary bubble motion by pushing and pulling it with optical radiation pressure force and by thermocapillary Marangoni effect, respectively. The latter facilitates interactions over millimeter-scale distances, which are otherwise unachievable. Apart from exploring new physical effects, mediating long-range interactions can find a use in a range of applications including drug design and screening, photochemistry, design of colloidal suspensions, and many others.

physics.optics↗

arXiv2024

Nanojet Visualization and Dark-field Imaging of Optically Trapped Vaterite Capsules with Endoscopic Illumination

Optical responsivity grants biomedical capsules additional capabilities, promoting them towards multifunctional theragnostic nanodevices. In this endeavor, screening candidates under conditions that closely resemble in situ environments is crucial for both the initial optimization and the subsequent inspection stages of development and operation. Optical tweezers equipped with dark-field spectroscopy are among the preferable tools for nanoparticle imaging and refractometry. However, the effectiveness of conventional illumination and light collection arrangements for inspecting anisotropic complex inner composition particles is quite limited due to reduced collection angles, which can result in the omission of features in scattering diagrams. Here we introduce an endoscopic dark-field illumination scheme, where light is launched on an optically trapped particle from a single-mode fiber, immersed into a fluid cell. This arrangement disentangles illumination and collection paths, thus allowing the collection of scattered light with a very high numerical aperture. This methodology is applied to vaterite nanocapsules, which are known to possess strong anisotropic responses. Tweezer configuration allows revealing optical properties for different crystallographic orientations of vaterite, which is complex to do otherwise. Furthermore, endoscopic dark-field images reveal the emergence of polarization-dependent long-range photonic nanojets, which are capable of interacting with nearby particles, demonstrating a new pathway for nanojet image formation.

physics.optics↗