arXiv subjects

Eduard Muslimov

Publications and source records attributed to Eduard Muslimov.

27 records · Page 2Linked to original sources

arXiv2018

POLLUX: a UV spectropolarimeter for the LUVOIR space telescope project

The present paper describes the current baseline optical design of POLLUX, a high-resolution spectropolarimeter for the future LUVOIR mission. The instrument will operate in the ultraviolet (UV) domain from 90 to 390 nm in both spectropolarimetric and pure spectroscopic modes. The working range is split between 3 channels -- far (90-124.5 nm), medium (118.5-195 nm) and near (195-390 nm) UV. Each of the channels is composed of a polarimeter followed by an echelle spectrograph consisting of a classical off-axis paraboloid collimator, echelle grating with a high grooves frequency and a cross-disperser grating operating also as a camera. The latter component integrates some advanced technologies: it is a blazed grating with a complex grooves pattern formed by holographic recording, which is manufactured on a freeform surface. One of the key features underlying the current design is the large spectral length of each order ~6 nm, which allows to record wide spectral lines without any discontinuities. The modelling results show that the optical design will provide the required spectral resolving power higher than R ~ 120,000 over the entire working range for a point source object with angular size of 30 mas. It is also shown that with the 15-m primary mirror of the LUVOIR telescope the instrument will provide an effective collecting area up to 38 569 cm 2. Such a performance will allow to perform a number of groundbreaking scientific observations. Finally, the future work and the technological risks of the design are discussed in details.

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arXiv2018

Curved detectors for wide field imaging systems: impact on tolerance analysis

In the present paper we consider quantitative estimation of the tolerances widening in optical systems with curved detectors. The gain in image quality allows to loosen the margins for manufacturing and assembling errors. On another hand, the requirements for the detector shape and positioning become more tight. We demonstrate both of the effects on example of two optical designs. The first one is a rotationally-symmetrical lens with focal length of 25 mm, f-ratio of 3.5 and field of view equal to 72$^\circ$, working in the visible domain. The second design is a three-mirror anastigmat telescope with focal length of 250 mm, f-ratio of 2.0 and field of view equal to $4^\circ \times 4^\circ$. In both of the cases use of curved detectors allow to increase the image quality and substantially decrease the requirements for manufacturing precision

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arXiv2018

Advanced optical designs of curved detectors-based two-mirrors unobscured telescopes

In the present paper we consider a family of unobscured telescope designs with curved detectors. They are based on classical two-mirror schemes -- Ritchey-Chretien, Gregorian and Couder telescopes. It is shown that all the designs provide nearly diffraction limited image quality in the visible domain for $.4^\circ \times .4^\circ$ field of view with the f-number of 7. We also provide a brief ghost analysis and point on special features of the systems with curved detectors. Finally, the detector surface shape obtained in each case is analyzed and its' technological feasibility is demonstrated.

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arXiv2018

Spectrographs with holographic gratings on freeform surfaces: design approach and application for the LUVOIR mission

In the present paper we demonstrate the approach to use a holographic grating on a freeform surface for advanced spectrographs design. On the example POLLUX spectropolarimeter medium-UV channel we chow that such a grating can operate as a cross-disperser and a camera mirror at the same time. It provides the image quality high enough to reach the spectral resolving power of 126 359-133 106 between 11.5 and 195 nm, which is higher than the requirement. Also we show a possibility to use a similar element working in transmission to build an unobscured double-Schmidt spectrograph. The spectral resolving power reaches 2750 for a long slit. It is also shown that the parameters of both the gratings are feasible with the current technologies.

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arXiv2018

Experimental study of an advanced concept of moderate-resolution holographic spectrographs

We present the results of an experimental study of an advanced moderate-resolution spectrograph based on a cascade of narrow-band holographic gratings. The main goal of the project is to achieve a moderately high spectral resolutionwith R up to 5000 simultaneously in the 4300-6800 A visible spectral range on a single standard CCD, together with an increased throughput. The experimental study consisted of (1) resolution and image quality tests performed using the solar spectrum; and (2) a total throughput test performed for a number of wavelengths using a calibrated lab monochromator. The measured spectral resolving power reaches values over R>4000 while the experimental throughput is as high as 55%, which is in good agreement with the modeling results. Comparing the obtained characteristics of the spectrograph under consideration with the best existing spectrographs, we conclude that the used concept can be considered a very competitive and cheap alternative to the existing spectrographs of the given class. We propose several astrophysical applications for the instrument and discuss the prospect of creating its full-scale version.

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arXiv2017

Design of pre-optics for laser guide star wavefront sensor for the ELT

In the present paper, we consider the optical design of a zoom system for the active refocusing in laser guide star wavefront sensors. The system is designed according to the specifications coming from the Extremely Large Telescope (ELT)-HARMONI instrument, the first-light, integral field spectrograph for the European (E)-ELT. The system must provide a refocusing of the laser guide as a function of telescope pointing and large decentring of the incoming beam. The system considers four moving lens groups, each of them being a doublet with one aspherical surface. The advantages and shortcomings of such a solution in terms of the component displacements and complexity of the surfaces are described in detail. It is shown that the system can provide the median value of the residual wavefront error of 13.8-94.3 nm and the maximum value <206 nm, while the exit pupil distortion is 0.26-0.36% for each of the telescope pointing directions.

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arXiv2017

A fast, wide-field and distortion-free telescope with curved detectors for surveys at ultra-low surface brightness

We present the design of an all-reflective, bi-folded Schmidt telescope aimed at surveys of extended astronomical objects with extremely-low surface brightness. The design leads to a high image quality without any diffracting spider, along with a large aperture and field of view, with a small central obstruction which barely alters the PSF. As an example, we present the design of a high-quality, 36 cm diameter, fast ( f /2.5) telescope working in the visible with a large field of view (1.6°x 2.6°). The telescope can operate with a curved detector (or with a flat detector with a field flattener) and a set of filters. The entrance mirror is anamorphic and replaces the classical Schmidt entrance corrector plate. We show that this anamorphic primary mirror can be manufactured through stress polishing, avoiding high spatial frequency errors, and tested with a simple interferometer scheme. This prototype is intended to serve as a fast-track scientific and technological pathfinder for the future space-based MESSIER mission.

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arXiv2017

Combining freeform optics and curved detectors for wide field imaging: a polynomial approach over squared aperture

In the recent years a significant progress was achieved in the field of design and fabrication of optical systems based on freeform optical surfaces. They provide a possibility to build fast, wide-angle and high-resolution systems, which are very compact and free of obscuration. However, the field of freeform surfaces design techniques still remains underexplored. In the present paper we use the mathematical apparatus of orthogonal polynomials defined over a square aperture, which was developed before for the tasks of wavefront reconstruction, to describe shape of a mirror surface. Two cases, namely Legendre polynomials and generalization of the Zernike polynomials on a square, are considered. The potential advantages of these polynomials sets are demonstrated on example of a three-mirror unobscured telescope with F/#=2.5 and FoV=7.2x7.2°. In addition, we discuss possibility of use of curved detectors in such a design.

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arXiv2017

Advanced modelling of a moderate-resolution holographic spectrograph

In the present article we consider an accurate modeling of spectrograph with cascade of volume-phase holographic gratings. The proposed optical scheme allows to detect spectra in an extended wavelength range without gaps providing relatively high spectral resolution and high throughput. However, modeling and minimization of possible cross-talks between gratings and stray light in such a scheme represents a separate task. We use analytical equations of coupled wave theory together with rigorous coupled wave analysis to optimize the gratings parameters and further apply the latter together with non-sequential raytracing algorithm to model propagation of beams through the spectrograph. The results show relatively high throughput up to 53% and absence of any significant cross-talks or ghost images even for ordinary holograms recorded on dichromated gelatin.

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