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Proceedings Paper • Open Access

Prospects for the design of an ultraviolet imaging Fourier transform spectrometer
Author(s): Philippe Lemaire

Paper Abstract

Recent results from solar observations in the far and extremeultraviolet (FUV/EUV) obtained from SOHO (SOlar and Heliospheric Observatory) and TRACE (Transition Region Camera) show the extreme variability of the solar atmosphere. Within the limited resolution of the instruments (1-2 arcseconds) horizontal and vertical velocities up-to 100 to 400 km s-1 have been measured. With an horizontal velocity of 100 km s-1 an one arsecond structure crosses the one arcsecond slit width of a classical slit spectrometer in less than 10 seconds. In the future, with higher angular resolution (e.g. 0.1 arcsecond), the capability to study small structures will be greatly reduced by a classical slit spectrometer.

To be able to characterize the small scale solar atmospheric structures formed in the 104 K to 106 K temperature range (which emit in the 30 to 180 nm wavelength range) a spectrometer without slit (or with wide slit) is required. At the same time to obtain an accurate measurement of the doppler velocity an high spectral resolution is needed. The two requirements, high spectral resolution and large slit, are difficult to be simultaneously fulfilled with a classical slit spectrometer within the limited volume of a space instrumentation. Also, we propose to use an Imaging Fourier Transform Spectrometer (IFTS) to provide simultaneously a bidimensionnal field and an accurate determination of line profiles and positions.

The development of Fourier Transform Spectrometers (FTS), although popular in the infrared, has been very limited in the UV/FUV by the lack of very high quality beam splitter. Since 10 years, the use of diffraction gratings as beam splitters has been suggested and few intruments have been built ([Chak 94]; [Clea 92]; [File 00]). These instruments illustrate some applications in the new wavelength domain opened by using a beam splitter grating, but do not yet provide the full capabilities of an FTS.

In this paper we present several optical schemes which can provide the full capabilities of a complete IFTS in the FUV/EUV spectral range.

Paper Details

Date Published: 21 November 2017
PDF: 11 pages
Proc. SPIE 10569, International Conference on Space Optics — ICSO 2000, 1056913 (21 November 2017); doi: 10.1117/12.2307873
Show Author Affiliations
Philippe Lemaire, Institut d'Astrophysique Spatiale (France)

Published in SPIE Proceedings Vol. 10569:
International Conference on Space Optics — ICSO 2000
Georges Otrio, Editor(s)

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