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Open AccessArticle

Spektr–UF Mission Spectrograph Space Qualified CCD Detector Subsystem

by

Andrey Shugarov

and

Mikhail Sachkov

Photonics 2023, 10(9), 1032; https://doi.org/10.3390/photonics10091032 - 08 Sep 2023

Viewed by 364

Abstract

Spektr–UF (World Space Observatory Ultraviolet, WSO-UV) is a Russian-led international collaboration aiming to develop a large space-borne 1.7 m Ritchey–Chretién telescope with science instruments to study the Universe in ultraviolet wavelengths. The WSO-UV spectrograph (WUVS) consists of three channels: two high-resolution channels (R [...] Read more.

Spektr–UF (World Space Observatory Ultraviolet, WSO-UV) is a Russian-led international collaboration aiming to develop a large space-borne 1.7 m Ritchey–Chretién telescope with science instruments to study the Universe in ultraviolet wavelengths. The WSO-UV spectrograph (WUVS) consists of three channels: two high-resolution channels (R = 50,000) with spectral ranges of 115–176 nm and 174–310 nm, and a low-resolution (R = 1000) channel with a spectral range of 115–305 nm. Each of the three channels has an almost identical custom detector consisting of a CCD inside a vacuum enclosure, and drive electronics. The main challenges of the WUVS detectors are to achieve high quantum efficiency in the FUV-NUV range, to provide low readout noise (3 e

^{-}

at 50 kHz) and low dark current (<12 e

^{-}

/pixel/hour), to operate with integral exposures of up to 10 h and to provide good photometric accuracy. A custom vacuum enclosure and three variants of a custom CCD272-64 sensor with different UV AR coatings optimised for each WUVS channel were designed. The enclosure prevents contamination and maintains the CCD at the operating temperature of −100

^{\circ}

C, while the temperature of the WUVS optical bench is +20

^{\circ}

C. A camera electronics box (CEB) that houses the CCD drive electronics was developed. Digital correlated double sampling technology allows for extremely low readout noise and flexible frequency for normal and binned pixel readout modes. This paper presents the WUVS detector design drivers, methods for extending the service life of the CCD sensors working with low signals in a space radiation environment and the key calculated parameters and results of the engineering qualification model qualification campaign. Full article

(This article belongs to the Special Issue Optical Systems for Astronomy)

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Open AccessArticle

Benefits of Intelligent Fuzzy Controllers in Comparison to Classical Methods for Adaptive Optics

by

Victor Costa

and

Wesley Beccaro

Photonics 2023, 10(9), 988; https://doi.org/10.3390/photonics10090988 - 30 Aug 2023

Viewed by 330

Abstract

Adaptive Optics (AO) systems have been developed throughout recent decades as a strategy to compensate for the effects of atmospheric turbulence, primarily caused by poor astronomical seeing. These systems reduce the wavefront distortions using deformable mirrors. Several AO simulation tools have been developed, [...] Read more.

Adaptive Optics (AO) systems have been developed throughout recent decades as a strategy to compensate for the effects of atmospheric turbulence, primarily caused by poor astronomical seeing. These systems reduce the wavefront distortions using deformable mirrors. Several AO simulation tools have been developed, such as the Object-Oriented, MATLAB, and Adaptive Optics Toolbox (OOMAO), to assist in the project of AO. However, the main AO simulators focus on AO models, not prioritizing the different control techniques. Moreover, the commonly applied control strategies in ground-based telescopes are based on Integral (I) or Proportional-Integral (PI) controllers. This work proposes the integration of OOMAO models to Simulink to support the development of advanced controllers and compares traditional controllers with intelligent systems based on fuzzy logic. The controllers were compared in three scenarios of different turbulence and atmosphere conditions. The simulations were performed using the characteristics/parameters of the Southern Astrophysical Research (SOAR) telescope and assessed with the Full Width at Half Maximum (FWHM), Half Light Radius (HLR), and Strehl ratio metrics to compare the performance of the controllers. The results demonstrate that adaptive optics can be satisfactorily simulated in OOMAO adapted to Simulink and thus further increase the number of control strategies available to OOMAO. The comparative results between the MATLAB script and the Simulink blocks designed showed a maximum relative error of

3 %

in the Strehl ratio and

1.59 %

in the FWHM measurement. In the assessment of the control algorithms, the fuzzy PI controller reported a

25 %

increase in the FWHM metrics in the critical scenario when compared with open-loop metrics. Furthermore, the fuzzy PI controller outperformed the results when compared with the I and PI controllers. The findings underscore the constraints of conventional control methods, whereas the implementation of fuzzy-based controllers showcases the promise of intelligent approaches in enhancing control performance under challenging atmospheric conditions. Full article

(This article belongs to the Special Issue Optical Systems for Astronomy)

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Open AccessArticle

Astronomical Camera Based on a CCD261-84 Detector with Increased Sensitivity in the Near-Infrared

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Photonics 2023, 10(7), 774; https://doi.org/10.3390/photonics10070774 - 04 Jul 2023

Viewed by 587

Abstract

Herein, we describe the design, implementation and operation principles of an astronomical camera system, based on a large-format CCD261-84 detector with an extremely thick 200 μm substrate. The DINACON-V controller was used with the CCD to achieve high performance and low noise. The [...] Read more.

Herein, we describe the design, implementation and operation principles of an astronomical camera system, based on a large-format CCD261-84 detector with an extremely thick 200 μm substrate. The DINACON-V controller was used with the CCD to achieve high performance and low noise. The CCD system photometric characteristics are presented. A spatial autocorrelation analysis of flat-field images was performed to reveal the dependence of substrate voltage on the lateral charge spreading. The investigation of the dispersion index for the optimal choice of exposure time is discussed. Studies of the patterns of fringes were carried out in comparison with previous detectors. The amplitude of fringes with CCD261-84 was significantly lower, compared to previous-generation detectors. The results of using a new camera for imaging and spectral observations at the Russian 6 m telescope with the SCORPIO-2 multimode focal reducer are considered. The developed CCD camera system makes it possible to significantly increase the sensitivity in the 800–1000 spectral range. Full article

(This article belongs to the Special Issue Optical Systems for Astronomy)

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Open AccessArticle

Optical Design of a Slitless Astronomical Spectrograph with a Composite Holographic Grism

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Photonics 2023, 10(4), 385; https://doi.org/10.3390/photonics10040385 - 31 Mar 2023

Viewed by 875

Abstract

In the present work, we consider an optical design of a slitless spectrograph for an existing 0.5 m-class telescope. This design concept has a number of advantages such as compact size, simplicity, and simultaneous coverage of a large field of view. A challenge [...] Read more.

In the present work, we consider an optical design of a slitless spectrograph for an existing 0.5 m-class telescope. This design concept has a number of advantages such as compact size, simplicity, and simultaneous coverage of a large field of view. A challenge with this design is correcting aberrations caused by placing a dispersing element in a converging beam. To overcome this issue, we propose to use a composite grism, which represents a combination of a prism and a volume-phase holographic grating, the latter which is split into zones with independently optimized parameters. We demonstrate two designs of such a grism. In both designs, the spectrograph operates in the range of 450–950 nm in an

F / 6.8

beam and covers a field of view of 35.6

^{'}

× 7.2

^{'}

. Through advanced modeling, it is shown that a composite grism having four rectangular zones with different thickness and index modulation depth of the hologram and recorded with an auxiliary deformable mirror decreases the astigmatic elongation by a factor of 85, increases the spectral resolving power by 4.4 times, and reaches

R 1389

while increasing the average diffraction efficiency by a factor of

1.31

. If we reduce the number of zones to only two, replace the deformable mirror with two static corrector plates, and fix the hologram thickness, the corresponding performance gains still remain high: the astigmatism is reduced by a factor of 61, the spectral resolving power is up to

1.7

times higher, reaching

R 1067

, and the efficiency is increased by a factor of

1.27

. This shows that the proposed design allows the construction of a simple and compact instrument, providing high performance over the entire field of view and spectral range. Full article

(This article belongs to the Special Issue Optical Systems for Astronomy)

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Open AccessArticle

Wavefront Sensing by a Common-Path Interferometer for Wavefront Correction in Phase and Amplitude by a Liquid Crystal Spatial Light Modulator Aiming the Exoplanet Direct Imaging

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Photonics 2023, 10(3), 320; https://doi.org/10.3390/photonics10030320 - 16 Mar 2023

Viewed by 896

Abstract

We implemented the common-path achromatic interfero-coronagraph both for the wavefront sensing and the on-axis image component suppression, aiming for the stellar coronagraphy. A common-path achromatic interfero-coronagraph has its optical scheme based on a nulling rotational-shear interferometer. The angle of rotational shear can be [...] Read more.

We implemented the common-path achromatic interfero-coronagraph both for the wavefront sensing and the on-axis image component suppression, aiming for the stellar coronagraphy. A common-path achromatic interfero-coronagraph has its optical scheme based on a nulling rotational-shear interferometer. The angle of rotational shear can be chosen at a small angular extent of about 10 deg. Such a small angular shear maintains the coronagraphic contrast degradation known as the stellar leakage effect, caused by a finite stellar size. We study the phase and amplitude wavefront control by a liquid crystal spatial light modulator of reflection type which is used as the pixilated active adaptive optics unit. Therefore, adaptive optics perform a wavefront-correcting input toward a stellar interfero-coronagraph aiming at the direct exoplanet imaging. Presented here are both the numeric evaluations and the lab experiment stand to prove the declared functionality output. Full article

(This article belongs to the Special Issue Optical Systems for Astronomy)

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Open AccessArticle

Statistical Tool Size Study for Computer-Controlled Optical Surfacing

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Photonics 2023, 10(3), 286; https://doi.org/10.3390/photonics10030286 - 09 Mar 2023

Cited by 1 | Viewed by 794

Abstract

Over the past few decades, computer-controlled optical surfacing (CCOS) systems have become more deterministic. A target surface profile can be predictably achieved with a combination of tools of different sizes. However, deciding the optimal set of tool sizes that will achieve the target [...] Read more.

Over the past few decades, computer-controlled optical surfacing (CCOS) systems have become more deterministic. A target surface profile can be predictably achieved with a combination of tools of different sizes. However, deciding the optimal set of tool sizes that will achieve the target residual error in the shortest run time is difficult, and no general guidance has been proposed in the literature. In this paper, we present a computer-assisted study on choosing the proper tool size for a given surface error map. First, we propose that the characteristic frequency ratio (CFR) can be used as a general measure of the correction capability of a tool over a surface map. Second, the performance of different CFRs is quantitatively studied with a computer simulation by applying them to guide the tool size selection for polishing a large number of randomly generated surface maps with similar initial spatial frequencies and root mean square errors. Finally, we find that CFR = 0.75 achieves the most stable trade-off between the total run time and the number of iterations and thus can be used as a general criterion in tool size selection for CCOS processes. To the best of our knowledge, the CFR is the first criterion that ties tool size selection to overall efficiency. Full article

(This article belongs to the Special Issue Optical Systems for Astronomy)

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Open AccessArticle

EXPLANATION: Exoplanet and Transient Event Investigation Project—Optical Facilities and Solutions

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Vladimir Plokhotnichenko

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Show full author list Hide full author list

Photonics 2022, 9(12), 950; https://doi.org/10.3390/photonics9120950 - 08 Dec 2022

Viewed by 1283

Abstract

Over the past decades, the achievements in astronomical instrumentation have given rise to a number of novel advanced studies related to the analysis of large arrays of observational data. One of the most famous of these studies is a study of transient events [...] Read more.

Over the past decades, the achievements in astronomical instrumentation have given rise to a number of novel advanced studies related to the analysis of large arrays of observational data. One of the most famous of these studies is a study of transient events in the near and far space and a search for exoplanets. The main requirements for such kinds of projects are a simultaneous coverage of the largest possible field of view with the highest possible detection limits and temporal resolution. In this study, we present a similar project aimed at creating an extensive, continuously updated survey of transient events and exoplanets. To date, the core of the project incorporates several 0.07–2.5 m optical telescopes and the 6-m BTA telescope of the Special Astrophysical Observatory of RAS (Russia), a number of other Russian observatories and the Bonhyunsan observatory of the Korea Astronomy and Space Science Institute (South Korea). Our attention is mainly focused on the description of two groups of small, wide-angle optical telescopes for primary detection. All the telescopes are originally designed for the goals of the project and may be of interest to the scientific community. A description is also given for a new, high-precision optical spectrograph for the Doppler studies of transient and exoplanet events detected within the project. We present here the philosophy, expectations and first results obtained during the first year of running the project. Full article

(This article belongs to the Special Issue Optical Systems for Astronomy)

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Open AccessArticle

Image Degradation Model for Dynamic Star Maps in Multiple Scenarios

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Photonics 2022, 9(10), 673; https://doi.org/10.3390/photonics9100673 - 20 Sep 2022

Cited by 1 | Viewed by 695

Abstract

To meet the ground test requirements of star sensors, we establish the star map simulation algorithm and the interactive interface in multiple scenarios. The combination of the degradation model of star points, the imaging noise model, and the attitude disturbance model is introduced [...] Read more.

To meet the ground test requirements of star sensors, we establish the star map simulation algorithm and the interactive interface in multiple scenarios. The combination of the degradation model of star points, the imaging noise model, and the attitude disturbance model is introduced to solve the problem of different patterns of noise existing in the actual measurement, improving the traditional simulation model. In addition, a user-friendly interface design makes it easier for both scholars and average individuals to understand the parameters and then generate static single-frame star maps—or a series of dynamic sequence star maps—under various conditions. The results of the proposed star map simulation method are highly comparable to the actual captured star images, and this method can be applied for the tests and calibrations of star sensors. Full article

(This article belongs to the Special Issue Optical Systems for Astronomy)

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