Straylight analysis for the externally occulted Lyot solar coronagraph ASPIICS

The ESA formation Flying mission Proba-3 will y the giant solar coronagraph ASPIICS. The instrument is composed of a 1.4 meter diameter external occulting disc mounted on the Occulter Spacecraft and a Lyot-style solar coronagraph of 50mm diameter aperture carried by the Coronagraph Spacecraft positioned 144 meters behind. The system will observe the inner corona of the Sun, as close as 1.1 solar radius. For a solar coronagraph, the most critical source of straylight is the residual diffracted sunlight, which drives the scientific performance of the observation. This is especially the case for ASPIICS because of its reduced field-of-view close to the solar limb. The light from the Sun is first diffracted by the edge of the external occulter, and then propagates and scatters inside the instrument. There is a crucial need to estimate both intensity and distribution of the diffraction on the focal plane. Because of the very large size of the coronagraph, one cannot rely on representative full scale test campaign. Moreover, usual optics software package are not designed to perform such diffraction computation, with the required accuracy. Therefore, dedicated approaches have been developed in the frame of ASPIICS. First, novel numerical models compute the diffraction profile on the entrance pupil plane and instrument detector plane (Landini et al., Rougeot et al.), assuming perfect optics in the sense of multi-reflection and scattering. Results are confronted to experimental measurements of diffraction. The paper reports the results of the different approaches.

[1]  J. Goodman Introduction to Fourier optics , 1969 .

[2]  B. Lyot The study of the solar corona and prominences without eclipses (George Darwin Lecture, 1939) , 1939 .

[3]  Cédric Thizy,et al.  Recent achievements on ASPIICS, an externally occulted coronagraph for PROBA-3 , 2016, Astronomical Telescopes + Instrumentation.

[4]  Cédric Thizy,et al.  Development of ASPIICS: a coronagraph based on Proba-3 formation flying mission , 2018, Astronomical Telescopes + Instrumentation.

[5]  A Llebaria,et al.  Experimental study of external occulters for the large angle and spectrometric coronagraph 2: LASCO-C2. , 2000, Applied optics.

[6]  Serge Koutchmy,et al.  Space-borne coronagraphy , 1988 .

[7]  J W EVANS A photometer for measurement of sky brightness near the sun. , 1948, Journal of the Optical Society of America.

[8]  Cédric Thizy,et al.  Preliminary evaluation of the diffraction behind the PROBA 3/ASPIICS optimized occulter , 2016, Astronomical Telescopes + Instrumentation.

[9]  P. Lamy,et al.  The Large Angle Spectroscopic Coronagraph (LASCO) , 1995 .

[10]  Damien Galano,et al.  Performance of the hybrid externally occulted Lyot solar coronagraph - Application to ASPIICS , 2017 .

[11]  Y. Stockman,et al.  Design and modelisation of ASPIICS optics , 2015, SPIE Optical Engineering + Applications.

[12]  Cédric Thizy,et al.  Test plan for the PROBA3/ASPIICS scaled model measurement campaign , 2017, Optical Engineering + Applications.

[13]  Daniel Asoubar,et al.  Scaled model guidelines for solar coronagraphs' external occulters with an optimized shape. , 2017, Optics letters.

[14]  S. V. Shestov,et al.  Influence of misalignments on the performance of externally occulted solar coronagraphs. Application to PROBA-3/ASPIICS , 2018 .

[15]  Claude Aime,et al.  Theoretical performance of solar coronagraphs using sharp-edged or apodized circular external occulters , 2013 .

[16]  C. Aime,et al.  Total coronagraphic extinction of rectangular apertures using linear prolate apodizations , 2002 .

[17]  Philippe Lamy,et al.  ASPIICS: a giant coronagraph for the ESA/PROBA-3 Formation Flying Mission , 2010, Astronomical Telescopes + Instrumentation.

[18]  Silvano Fineschi,et al.  External occulter laboratory demonstrator for the forthcoming formation flying coronagraphs. , 2011, Applied optics.