A Broad Band Imager for the European Solar Telescope

1. A Broad Band Imager for the European Solar Telescope Matteo Munari & Salvo Scuderi INAF – Osservatorio Astrofisico di Catania Massimo Cecconi INAF – FGG Telescopio Nazionale Galileo 1st SPRING Workshop, Nov 26-28, 2103

2. Broad Band Imager • The EST broad band imager (BBI) is one of the focal plane instruments foreseen for the EST Telescope. • It is an imaging instrument whose function is to obtain diffraction limited images over the full field of view of EST at multiple wavelengths and high frame rate. • Its scientific objective is the study of fundamental physical processes at their intrinsic scales in the Sun’s atmosphere. 1st SPRING Workshop, Nov 26-28, 2103

3. Science Cases 1st SPRING Workshop, Nov 26-28, 2103

4. BBI Characteristics 1st SPRING Workshop, Nov 26-28, 2103

5. Operational Wavelenghts 1st SPRING Workshop, Nov 26-28, 2103

6. EST Light Distribution 1st SPRING Workshop, Nov 26-28, 2103

7. Optical design: Constraints Telescope • On axis Gregorian • 4 meter entrance pupil diameter • F/50, telecentric • Focal plane of 2'x2' side • Aberration free optical system Instrument • Filters diameters < 10cm • Detector format  4k x 4k • Pixel size  10 microns • Back Focal distance  500 mm 1st SPRING Workshop, Nov 26-28, 2103

8. Optical design: Layout • Refractive Design • After evaluation of all refractive and reflective/refractive designs an all refractive design with filters in telecentric configuration has been chosen on the basis of performances and simplicity • Two arms • Two arms completely independent to optimize optical performances and throughput through appropriate choices of optics, coatings and detector. • BlueArm(for filters in the 380nm – 500nm range)  two channels each divided in three sub–channels • Red Arm(for filters in the 600nm – 900nm range)  one channel divided in three sub–channels • 3 identical channels • Divided in 3 sub-channels. • The sub–channels share the same optics  See the same aberrations. • Out of the three sub–channels of each channel, the first one hosts narrow band filters for chromospheric observations, the second one hosts in focus wide band filters used as reference for Multi-Object Multi-Frame Blind Deconvolution reconstruction (MOMFBD) and photospheric observations and the third one hosts out of focus wide band filters for phase diversity reconstruction of photosphericobservations. • Filters located after the beam separation, that is, near the detector. 1st SPRING Workshop, Nov 26-28, 2103

9. Optical design: Layout • Each channel has two alternative observing modes • Realized with the use of pick-up relays • Large FOV mode direct • High resolution mode folded • Flexibility  Each mode available independently on the various channels 1st SPRING Workshop, Nov 26-28, 2103

10. Optical Design: Characteristics • Channel Dimensions: 4.5x1.0x0.5m (Biggest element first doublet ~210mm diameter) • Observing modes data • High resolution: F/# =32; Scale=1.6’’/mm; Sampling=0.016’’/px; FoV size=64’’x64’’ • Large FoV: F/# =17; Scale=3.0’’/mm; Sampling=0.030’’/px; FoV size=2’x2’ • Both: Detector format: 4k x 4k; Pixel size=10 micron • 2x2 lenses in each mode (one common doublet) • 2 glasses used in symmetric way (Corning B19-61 & Schott KZFSN5) 1st SPRING Workshop, Nov 26-28, 2103

11. Optical Design: Generic Channel 4.5 m HR doublet Telescope Focal Plane Mirror FPA Large FOV doublet Common doublet BS 1.0 m FPA 1st SPRING Workshop, Nov 26-28, 2103

12. Performances: High Resolution Mode 2 px 4 px side 1’x1’ 4px 4px 4px 2px 2px 2px 1st SPRING Workshop, Nov 26-28, 2103

13. Performances: Large FoV Mode 2 px 4 px side 2’x2’ 4px 4px 4px 2px 2px 2px 1st SPRING Workshop, Nov 26-28, 2103

14. Performance: Throughput Lenses transmission (MgF2 coated) wavelength (µm) 1st SPRING Workshop, Nov 26-28, 2103

15. Mechanical Design Layout: Blue Arm 1500 mm 1640 mm 2400 mm 1500 mm 4200 mm 1st SPRING Workshop, Nov 26-28, 2103

16. Mechanical Design M2 The mechanical components and assemblies included in each BBI channel are: optical bench, dust/light proof cover, entrance shutter, optical mountings, mechanisms, and detector cryostat. High Res Doublet M1 M3 UCS Linear Stage BS1 Large FoV Doublet FPA FPA FPA Filter Holder BS2 1st SPRING Workshop, Nov 26-28, 2103

17. Mechanisms • Filter Holders : Sizes and type depend on filters • Focusing • Change of optical path: Filters & Telescope • Choice of most suitable optical element • Mode switching : change between large FOV and high resolution modes • Mechanism holding alignment target • Channel/Detector entrance shutter : detectors tests • Filters Temperature Control system • Polarizers : modulation of light intensity 1st SPRING Workshop, Nov 26-28, 2103

18. Filters: Critical Issues • Size • At least as big as the detector. • Diameters of 6 cm quasi-standard request • 8/9 cm still feasible but expensive in terms of money and time • According to manufacturers bigger dimensions are unrealistic • F/# & spectral shape • Large FoV  F/18 & High Resolution  F/32 • Central bandwidth shift towards blue • Broadening of the FWHM • Careful Design • Thermal Control • Temperature coefficients for interference filters  0.002–0 .02 nm/°C (Barr, Andover on line docs) • Spectral Band Shift  Intensity fluctuations • Temperature controlled within 1 degree or better depending on filter characteristics 1st SPRING Workshop, Nov 26-28, 2103

19. Detectors 1st SPRING Workshop, Nov 26-28, 2103

20. Conclusions • Optical design -> Advanced • Mechanical design -> Preliminary • Filters -> Critical (contacts with manufacturers) • Detectors -> Critical • Cost Estimate -> 850 k€ (no detector) 1st SPRING Workshop, Nov 26-28, 2103