EDP Sciences
Free access
Volume 467, Number 1, May III 2007
Page(s) 375 - 383
Section Astronomical instrumentation
DOI http://dx.doi.org/10.1051/0004-6361:20066287

A&A 467, 375-383 (2007)
DOI: 10.1051/0004-6361:20066287

Solar confocal interferometers for sub-picometer-resolution spectral filters

G. A. Gary1, C. Pietraszewski2, E. A. West1, and T. C. Dines2

1  National Space Science and Technology Center, Marshall Space Flight Center, Huntsville, AL, 35812, USA
    e-mail: Allen.Gary@nasa.gov
2  IC Optical Systems Ltd., Beckenham, Kent, BR34TW, UK
    e-mail: sales@icopticalsytems.com

(Received 22 August 2006 / Accepted 23 January 2007)

Aims.The confocal Fabry-Pérot interferometer allows sub-picometer spectral resolution of Fraunhofer line profiles. Such high spectral resolution is needed to keep pace with the higher spatial resolution of the new set of large-aperture solar telescopes. The line-of-sight spatial resolution derived for line profile inversions would then track the improvements of the transverse spatial scale provided by the larger apertures. In particular, profile inversion allows improved velocity and magnetic field gradients to be determined independent of multiple line analysis using different energy levels and ions. The confocal interferometer's unique properties allow a simultaneous increase in both étendue and spectral power. The higher throughput for the interferometer provides significant decrease in the aperture, which is important in spaceflight considerations.
Methods.We have constructed and tested two confocal interferometers. A slow-response thermal-controlled interferometer provides a stable system for laboratory investigation, while a piezoelectric interferometer provides a rapid response for solar observations.
Results. In this paper we provide design parameters, show construction details, and report on the laboratory test for these interferometers. The field of view versus aperture for confocal interferometers is compared with other types of spectral imaging filters. We propose a multiple etalon system for observing with these units using existing planar interferometers as pre-filters. The radiometry for these tests established that high spectral resolution profiles can be obtained with imaging confocal interferometers. These sub-picometer spectral data of the photosphere in both the visible and near-infrared can provide important height variation information. However, at the diffraction-limited spatial resolution of the telescope, the spectral data is photon starved due to the decreased spectral passband.

Key words: Sun: atmosphere -- instrumentation: interferometers -- Sun: magnetic fields -- Sun: general -- Sun: infrared

© ESO 2007

What is OpenURL?

The OpenURL standard is a protocol for transmission of metadata describing the resource that you wish to access.

An OpenURL link contains article metadata and directs it to the OpenURL server of your choice. The OpenURL server can provide access to the resource and also offer complementary services (specific search engine, export of references...). The OpenURL link can be generated by different means.

  • If your librarian has set up your subscription with an OpenURL resolver, OpenURL links appear automatically on the abstract pages.
  • You can define your own OpenURL resolver with your EDPS Account.
    In this case your choice will be given priority over that of your library.
  • You can use an add-on for your browser (Firefox or I.E.) to display OpenURL links on a page (see http://www.openly.com/openurlref/). You should disable this module if you wish to use the OpenURL server that you or your library have defined.