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A Broad Band Imager for the European Solar Telescope
Matteo Munari & Salvo ScuderiINAF – Osservatorio Astrofisico di Catania
Massimo CecconiINAF – 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 CasesObserving Program Filters FOV Angular
Resolution SNR CadenceNumber 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 845
22 (goal 33)Optimum 3030
0.1 100 5 s No
Internal structure of magnetic elements (2.1.2)
CN band head, G Band, blue and red continua Ca II H core & wing, Ca II 845
22 (goal 33)Optimum 3030
0.1 100 5 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 845
22 (goal 33)Optimum 3030
0.05 100 5 s No
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
22 (goal 33)Optimum 3030
0.1 100 10 s No
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 845
22 (goal 33)Optimum 3030
0.05 100 5 s No
Latitudinal distribution and structure of polar fields (2.1.6)
CN band head, G Band, blue continuum Ca II H core & wing, Ca II 845
22 (goal 33)Optimum 3030
0.05 100 10-30 s No
Network element dynamics (2.2.2) G Band 100100 TBD No
Highly variable phenomena in the chromosphere (2.3.2) Continua TBD 3030 0.2 30 s No
Sunspots (2.4.1) Continuum, G-band100100 Optimum 3030
0.05 0.05 s 2
Flares (2.6.1) Continua: 417 nm (Paschen), 840 nm (Brackett) 33 0.05 0.05 s 2
1st SPRING Workshop, Nov 26-28, 2103
BBI CharacteristicsNumber of spectral channels 3 channels working simultaneouslyObservation 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 0.04” @ 500 nmWavelength Coverage 390 nm – 900 nmWavelength Bandpass 0.05 to 0.5 nmWavelength Switching < 2 seconds Maximum bandpass shift 5x10-3nm (goal 3x10-3) @ 500nm, 30’’ from the field center
Transmission Total throughput > 30%
1st SPRING Workshop, Nov 26-28, 2103
Operational Wavelenghts Filter Number Filter Name C [nm] FWHM [nm] Spectral Feature
BBI-WF2 F395W 395.37 0.5 Ca II H continuum
BBI-NF2 F397N 396.88 0.05 Ca II H core
BBI-WF1 F388W 388.30 0.5 CN band head
BBI-NF1 F396N 396.47 0.05 Ca II H wing
BBI-WF2 F395W 395.37 0.5 Ca II H continuum
BBI-WF3 F417W 417.00 0.5 Paschen continuum
BBI-WF4 F430W 430.50 0.5 G band
BBI-WF5 F436W 436.39 0.5 G band continuum
BBI-NF3 F656N 656.28 0.1 H
BBI-WF6 F668W 668.40 0.5 H continuum
BBI-WF7 F840W 840.00 0.5 Brackett continuum
BBI-NF4 F854N 854.20 0.05 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 Channel4.5 m
1.0 m
Common doublet
Telescope Focal PlaneHR doublet
Large FOV doublet
FPA
FPA
BS
Mirror
1st SPRING Workshop, Nov 26-28, 2103
Performances: High Resolution Mode
2 px 4 px side
2px4px
2px4px
2px4px
1’x1’
1st SPRING Workshop, Nov 26-28, 2103
Performances: Large FoV Mode
2 px 4 px side
2px4px
2px4px
2px4px
2’x2’
1st SPRING Workshop, Nov 26-28, 2103
Performance: ThroughputLenses transmission (MgF2 coated)
wavelength (µm)
1st SPRING Workshop, Nov 26-28, 2103
Mechanical Design Layout: Blue Arm
2400
mm1640 mm
1500 mm
1500 mm
4200 mm
1st SPRING Workshop, Nov 26-28, 2103
Mechanical DesignThe mechanical components and assemblies included in each BBI channel are: optical bench, dust/light proof cover, entrance shutter, optical mountings, mechanisms, and detector cryostat.
UCSM1
M2
M3BS1
BS2
FPAFPA
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 3964.70, 0.50
6562.80 ,1.00
8542.00, 0.50
12.5 3964.18, 1.16
6561.94, 2.02
8540.88, 2.30
25 3964.56, 0.59
6562.58, 1.14
8541.72, 0.78
35 3964.63, 0.53
6562.69, 1.06
8541.85, 0.60
Detectors
Format 4k x 4k 6k x 6k (FoV: 2’x2’)
Pixel Dimensions 10 – 20 micron
Full Well Depth > 60000 e–
Frame Rate 20 – 100 frame/s
Bit resolution 16
Read Out Noise < 10 e–
Dark Current Few e–/s
Quantum Efficiency > 60% @ < 400 nm> 80% @ > 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