Design of a hybrid refractive-diffractive telescope for observations in UV
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Design of a hybrid refractive-diffractive telescope for observations in UV Grzegorz Fluder 1,2 Received: 9 January 2020 / Accepted: 10 July 2020/ # The Author(s) 2020
Abstract Telescopes are one of the common types of satellite payloads. They are used both for Earth and astronomical observations. By using space telescopes it is possible to eliminate the negative effect of the atmosphere on image quality. Additionally, observations in some spectral ranges can be performed only from space due to absorption of certain wavelengths in the atmosphere. One such range is UV below 300 nm, which is of particular interest when it comes to the investigation of hot objects. Reflective telescopes are commonly used in this spectral range, although many classical designs are limited in their useful field of view to values below 1°. In this paper a hybrid refractive-diffractive telescope design working in a 200 nm – 300 nm spectral range with a field of view 10°×10° is proposed. Its performance is compared to purely refractive and reflective systems and significant improvement in the imaging quality of the system and decrease of its size is shown. The choice of the diffractive element type is explained. Parameters of the systems are based on the requirements for a proposed Polish mission UVSat which aims to enable long-term observations of a large number of stars exhibiting UV variance. Keywords Telescope . Hybrid imaging system . Space telescope . Diffractive optical
element . Ultraviolet astronomy
1 Introduction Ultraviolet astronomy offers unique possibilities to investigate hot object, such as young and massive stars, stars at the final stages of their evolution and others, such as active galactic nuclei. Due to the high absorption of Earth’s atmosphere in this * Grzegorz Fluder [email protected]
1
Solaris Optics S.A, Sobieskiego 49, 05-410 Józefów, Poland
2
Institute of Micromechanics and Photonics, Photonics Engineering Division, Warsaw University of Technology, 8 Św. A. Boboli St, 02-525 Warsaw, Poland
Experimental Astronomy
spectral range observations may be performed only from space. There are several satellite missions currently being realized or developed offering the possibility of UV observations. They include among others World Space Observatory – Ultraviolet [1] Astrosat with its Ultraviolet Imaging Telescope (UVIT) [2], Large Ultraviolet Optical Infrared Surveyor (LUVOIR) [3] and Hubble Space Telescope with several instruments, including the Space Telescope Imaging Spectrograph [4] The concept of a Polish satellite mission UVSat has been first proposed in 2013 aiming to enable longterm observations of even several hundred objects simultaneously [5]. Thanks to this unique feature a very wide range of objects exhibiting UV variance may be observed and analyzed. Depending on the object this variance could last from single seconds even up to years. All the data gathered during such observations could lead to development and verification of different models, e.g. in the field of asteroseism
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