arXiv subjects

Alexey Shitvov

Publications and source records attributed to Alexey Shitvov.

5 recordsLinked to original sources

arXiv2026

Filter and baffle design for the short-wavelength camera on SOLAR-C EUVST

SOLAR-C, which is scheduled to launch in the late 2020s with the Extreme Ultraviolet High-Throughput Spectroscopic Telescope (EUVST), will deliver EUV spectroscopy of the solar atmosphere with unprecedented temperature coverage and resolution. We present the optical design and mechanical impacts for the short-wavelength camera, and how our design choices affect scientific performance using complete forward modelling. We discuss the design and optical impact of the thin-film aluminium filter and supporting mesh, including diffraction and shadowing effects in spectral and spatial dimensions. We analyse this using our own Fourier optics method and analytical modelling, and quantify the scientific impact using forward modelling driven by a simulated solar atmosphere. We address the vulnerability of thin-film filters during launch depressurisation using vacuum chamber testing. We describe the stray-light baffle design and low-scatter coatings which suppress visible stray light.

astro-ph.IM↗

arXiv2026

Pre-flare and active region plasma flows and structure seen by the short wavelength camera on SOLAR-C/EUVST

The mechanisms triggering solar flares and driving coronal heating occur across wide temperature ranges on small spatial scales and short timescales, making them difficult to observe with current instrumentation. The upcoming SOLAR-C mission, launching in the late 2020s, will provide unprecedented plasma diagnostic capability with its high-throughput extreme-ultraviolet (EUV) spectroscopic telescope (EUVST), capable of ~0.2 arcsec/pix spatial sampling (~0.4 arcsec resolution), continuous temperature coverage from 0.02-15 MK, and exposure times down to 0.5 seconds. We present forward modelling of the spectrograph's short wavelength camera (170-210 {\AA}; SOLAR-C/EUVST-SW) and its response to log T~6.2 coronal plasma in a three-dimensional MHD-simulated pre-flare active region. We compare this performance to that of the previous-generation EUV Imaging Spectrometer (EIS) on Hinode (SOLAR-B). Our results demonstrate that SOLAR-C/EUVST can distinguish individual flux tubes in simulated active region loops which Hinode/EIS cannot resolve. In simulated pre-flare plasma, SOLAR-C/EUVST captures sharp velocity gradients between adjacent upflowing and downflowing plasma which Hinode/EIS is unable to resolve. Doppler velocity measurement accuracy will reach better than 1 km/s in active regions. We show that this next-generation spectrograph can be expected to directly observe processes potentially related to flare triggering, such as plasma flows from low-altitude reconnection linked to emerging flux, and determine whether active region loops consist of a small number of strands or the hundreds predicted by magnetic reconnection-induced nanoflare heating models.

astro-ph.SR↗

arXiv2025

A metamaterial telescope at millimetre wavelengths

In this paper we present a novel telescope composed exclusively of thin, flat optical elements, each being a hot-pressed multi-layered structure combining the properties of a lens, its anti-reflection coating and frequency selection or filtering. We discuss the design process, from fundamental physical metamaterial properties of the single periodic cell structure to the lens concept, which constitutes the building block of the telescope design, and the iterative process that is part of the lens optimization. We provide the results of a laboratory test campaign for different telescope designs based on three-lens arrangements. Beam cuts and focus measurements both on- and off-axis are compared with models showing good agreement. We conclude that a broad-band mm-wave complete telescope system consisting entirely of metamaterial flat lenses has been built and tested, showing comparable performance with conventional state-of-the-art refractive telescopes in the same wavelength region. This new broadband design, highly efficient at frequencies between 90 and 190 GHz, offers multiple advantages. These include a $> 80\%$ weight reduction, reduced issues tied to coating-survivability at cryogenic temperatures caused by differential contraction exacerbated by non-flat surfaces, as well as a reduction in the overall number of components and mechanical mounts.

astro-ph.IM↗

arXiv2023

Thin flexible multi-octave metamaterial absorber for millimetre wavelengths

Development of novel radiation-absorbent materials and devices for millimetre and submillimetre astronomy instruments is a research area of high interest, and with substantial engineering challenges. Alongside low-profile structure and ultra-wideband performance in a wide range of angles of incidence, advanced absorbers in CMB instruments are aimed at reducing optical systematics, notably instrument polarisation, far beyond previous specifications. This paper presents an innovative design of flat thin flexible absorber operating in a wide frequency range of 80-400 GHz. The structure comprises a combination of sub-wavelength metal-mesh capacitive and inductive grids and dielectric layers, making use of the magnetic mirror concept for large bandwidth. The overall stack thickness is a quarter of the longest operating wavelength and is close to the theoretical limit stipulated by Rozanov criterion. The test device is designed to operate at 22.5deg. incidence. The iterative numerical-experimental design procedure of the new absorber is discussed in detail, as well as the practical challenges of its manufacture. A well-established mesh-filter fabrication process has been successfully employed for prototype fabrication, which ensures cryogenic operation of the hot-pressed quasi-optical devices. The final prototype, extensively tested in quasi-optical testbeds using a Fourier-transform spectrometer and a vector network analyser, demonstrated performance closely matching the finite-element analysis simulations, viz., greater than 99% absorbance for both polarisations, with only 0.2% difference, across the frequency band of 80-400 GHz. The angular stability for up to +/-10deg. has been confirmed by simulations. To the best of the authors knowledge, this is the first successful implementation of a low-profile ultrawideband metamaterial absorber for this frequency range and operating conditions.

astro-ph.IM↗

arXiv2021

Design and experimental investigation of a planar metamaterial Silicon based lenslet

The next generations of ground-based cosmic microwave background experiments will require polarisation sensitive, multichroic pixels of large focal planes comprising several thousand detectors operating at the photon noise limit. One approach to achieve this goal is to couple light from the telescope to a polarisation sensitive antenna structure connected to a superconducting diplexer network where the desired frequency bands are filtered before being fed to individual ultra-sensitive detectors such as Transition Edge Sensors. Traditionally, arrays constituted of horn antennas, planar phased antennas or anti-reflection coated micro-lenses have been placed in front of planar antenna structures to achieve the gain required to couple efficiently to the telescope optics. In this paper are presented the design concept and a preliminary analysis of the measured performances of a phase-engineered metamaterial flat-lenslet. The flat lens design is inherently matched to free space, avoiding the necessity of an anti-reflection coating layer. It can be fabricated lithographically, making scaling to large format arrays relatively simple. Furthermore, this technology is compatible with the fabrication process required for the production of large-format lumped element kinetic inductance detector arrays which have already demonstrated the required sensitivity along with multiplexing ratios of order 1000 detectors/channel.

astro-ph.IM↗