F. Cavallini

The Fabry-Pérot interferometer prototype for the ADAHELI solar small mission

ADAHELI ADvanced Astronomy for HELIophysics is a solar satellite designed to investigate the fast dynamics of the solar photosphere and chromosphere performing visible and NIR broad-band and monochromatic observations of selected atomic lines. ADAHELI is an Italian Space Agency (ASI) project, approved for a feasibility study within the ASI Small Missions call. ISODY Interferometer for SOlar DYnamics is a Gregorian telescope and its focal plane suite (FPS). The FPS is composed of a high-resolution fast acquisition system, based upon a tandem of Fabry-Pérot interferometers operating in the visible and NIR regions on selected solar atmospheric lines, a broad band channel, and a correlation tracker used as image stabilization system. In this contribution we describe the Fabry-Pérot étalon prototype, based on the capacitance-stabilised concept, realized in our laboratory to perform preliminary mechanical and optical tests with a view to a future Fabry-Pérot étalon prototype for space application.

The telescope and the double Fabry-Pérot interferometer for the ADAHELI solar space mission

ADvanced Astronomy for HELIophysics (ADAHELI) is a Small Mission to study the structure and fast dynamics of the low solar atmosphere, performing Visible-NIR monochromatic and broad-band observations. The mission will achieve millimeter full disk observations as well. The ADAHELI Team has succesfully completed, in December 2008, the Phase A study awarded by the Italian Space Agency (ASI). The Interferometer for SOlar Dynamics (ISODY), on board the ADAHELI satellite, comprises a Gregorian telescope and its focal plane suite. The advanced design focal plane suite uses fast CMOS cameras for investigating photospheric and chromospheric fast dynamics and structure. ISODY is equipped with a pioneering focal plane suite composed of a spectral channel, based upon a tandem of Fabry-Perot interferometers operating in the visible-NIR spectral region, a broad band channel for high resolution imaging, and a correlation tracker used as an image stabilization system. ADAHELIs mission profile has been tailored to limit the spacecrafts radial velocity in the Sunward direction, to not exceed ±4 km/s, during 95% of the yearly orbit, to allow a continuous use of the on-board interferometer.

Optical design of a near-infrared imaging spectropolarimeter for the Advanced Technology Solar Telescope

Abstract. In designing the optics of an imaging multi-etalon spectropolarimeter as a post-focus instrument for the Advanced Technology Solar Telescope (ATST), many constraints must be considered. Among these are the large entrance pupil diameter of the telescope (4 m), the demanded large field of view (≥90  arc sec), high spectral resolving power (≥200,000), and limited field-dependent blue-shift of the instrumental profile [≤3 full width at half maximum (FWHM)], which require Fabry-Perot interferometers of large diameter (≥200  mm), lighted by highly collimated beams. This implies large optical elements and long optical paths. Moreover, to use interference pre-filters with a relatively small diameter (≤70  mm) and placed between the interferometers to reduce the inter-reflections in axial-mount, a “pupil adapter” must be included with a further increase of the optical path length. Although a multi-etalon spectropolarimeter works in quasi-monochromatic light, the Fraunhofer lines of interest cover a wide range of wavelengths (850 to 1650 nm), which demands a good chromatic aberration control. A low instrumental polarization (≤0.5%) is also required to allow a high polarimetric precision. Finally, some secondary optical paths are required to perform the initial instrumental setup and to secure the best instrumental performances. A diffraction-limited optical solution for ATST is described that fulfills all the above requirements in a relative small volume.