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

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

Science Cases Observing ProgramFiltersFOV Angular Resolution SNRCadence Number of simultaneous Channels Chromospheric response to convective collapse (2.1.1) CN band head, G Band, blue and red continua Ca II H core & wing, Ca II  2 (goal 3  3) Optimum 30  30   0.1  sNo Internal structure of magnetic elements (2.1.2) CN band head, G Band, blue and red continua Ca II H core & wing, Ca II  2 (goal 3  3) Optimum 30  30   0.1  1005 s (  30 s) No Emergence and evolution of fields in granular convection (2.1.3) CN band head, G Band, blue and red continua Ca II H core & wing, Ca II  2 (goal 3  3) Optimum 30  30   0.05  sNo Physics of flux cancellations in the solar atmosphere (2.1.4) G Band, blue and red continua Ca II H core & wing, Ca II 845, H  2  2 (goal 3  3) Optimum 30  30   0.1  sNo Physical properties and evolution of internetwork fields (2.1.5) CN band head, G Band, blue and red continua Ca II H core & wing, Ca II  2 (goal 3  3) Optimum 30  30   0.05  sNo Latitudinal distribution and structure of polar fields (2.1.6) CN band head, G Band, blue continuum Ca II H core & wing, Ca II  2 (goal 3  3) Optimum 30  30   0.05  sNo Network element dynamics (2.2.2)G Band 100  100  TBDNo Highly variable phenomena in the chromosphere (2.3.2) Continua TBD  30  30  0.2  30 sNo Sunspots (2.4.1)Continuum, G-band 100  100  Optimum 30  30  0.05  0.05 s 2 Flares (2.6.1) Continua: 417 nm (Paschen), 840 nm (Brackett) 3   0.05 s2 1st SPRING Workshop, Nov 26-28, 2103

BBI Characteristics Number of spectral channels 3 channels working simultaneously Observation modes -High Resolution -to exploit the diffraction limited quality of the telescope + MCAO system (FoV: 1’x1’) -Large Field of View -Seeing limited angular resolution to exploit the full corrected telescope field of view (FoV: 2’x2’) Field of View 2’x2’ Angular Resolution 500 nm Wavelength Coverage 390 nm – 900 nm Wavelength Bandpass 0.05 to 0.5 nm Wavelength Switching < 2 seconds Maximum bandpass shift 5x10 -3 nm (goal 3x nm, 30’’ from the field center Transmission Total throughput > 30% 1st SPRING Workshop, Nov 26-28, 2103

Operational Wavelenghts Filter NumberFilter Name C [nm] FWHM [nm]Spectral Feature BBI-WF2 F395W Ca II H continuum BBI-NF2 F397N Ca II H core BBI-WF1 F388W CN band head BBI-NF1 F396N Ca II H wing BBI-WF2 F395W Ca II H continuum BBI-WF3 F417W Paschen continuum BBI-WF4 F430W G band BBI-WF5 F436W G band continuum BBI-NF3 F656N HH BBI-WF6 F668W H  continuum BBI-WF7 F840W Brackett continuum BBI-NF4 F854N Ca II IR 1st SPRING Workshop, Nov 26-28, 2103

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

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

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. Blue Arm (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 photospheric observations. – Filters located after the beam separation, that is, near the detector. 1st SPRING Workshop, Nov 26-28, 2103

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

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

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

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

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

Performance: Throughput Lenses transmission (MgF 2 coated) wavelength (µm) 1st SPRING Workshop, Nov 26-28, 2103

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

Mechanical Design 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. UCS M1 M2 M3 BS1 BS2 FPA Filter Holder High Res Doublet Large FoV Doublet Linear Stage 1st SPRING Workshop, Nov 26-28, 2103

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

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 F/#Central wavelength, FWHM (A) Nominal , , , , , , , , , , , , 0.60

Detectors Format 4k x 4k  6k x 6k (FoV: 2’x2’) Pixel Dimensions 10 – 20 micron Full Well Depth > e– Frame Rate 20 – 100 frame/s Bit resolution 16 Read Out Noise < 10 e– Dark Current Few e–/s Quantum Efficiency > < 400 nm > > 400 nm 1st SPRING Workshop, Nov 26-28, 2103

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