Imaging,Visible, Tunable, Narrow-Passband Filter System

1
Imaging,Visible, Tunable, Narrow-Passband Filter
System

• A Multiple Fabry-Perot Etalon Interferometer for
  the ATST
• G. Allen Gary/MSFC, K. S. Balasubramaniam/NSO,
  Michael Sigwarth/KIS, Thomas Kentischer/KIS, Gil
  Moretto/NSO, and
• the ATST team

27 August 2003 ATST Conceptual Design Review
2
Outline of the Presentation

• The MFPI concept
• Baseline Instrument Triple Fabry-Perot Etalons
• Optical Layout and Interface for the ATST
• Technology development
• Estimated Cost
• Science

3
Fabry-Perot Etalons

• Commensurate spectral resolution for high
  resolution imaging at telescope resolution
• 1/250,000 at 500 nm
• High light throughput
• Sufficient number of spectral samples within
  solar oscillation periods, solar feature changes
• Rapid tuning, calibrations
• Better compensation for atmospheric effects,
• And stability
• Provides simple spectroscopy and polarimetry of
  multiple lines in encompassing fashion
• Polarization fidelity and purity
• Uses commercial technology
• Visible range coverage (450nm-750nm)

4
Comparison with other alternatives
ATST Visible Narrow-Band Filter Candidates Air-Gap Fabry-Perot Interferometer Solid Fabry-Perot Interferometer Lyot Birefringent Filter Solid Polarizing Michelson Interferometer
FWHM(minimum) 2pm (NSO - Dual Etalon) 10pm (APL - Flare Genesis) 10pm (LMSAL - SOUP) 2-10pm (NSO - GONG)
Transmittance Prefilter Factor Total Throughput 90 60 50 30 60 50 14 60 8 90 8 - 50 8-50
Pre-Filter Requirement 0.2nm Interference filter 0.2nm Interference filter 0.2nm Interference Filter Lyot plus 0.2nm Interf. filter
FOV Variation Dl/l q2 Dl/l q2/n2 Dl/l q2(ne-no)/neno2 Dl/l q2(p2/n2- p1/n1)/ 2(p2n2- p1n1)
Tuning Device Piezoelectric Lithium niobate Rotating polarizers Rotating waveplates
Technology Requirements Large etalons, Ghost reflections, Mountings Thin elements, Superpolishing, Refractive index Improve Transmittance, Longer and thinner elements Multiple elements, Archomatic refractive index, Larger path differences
Operational Instruments KIS TESOS, USAF ISOON, ItalianUBI, Sac Peak Dual FPI Flare Genesis, Mees UH IMaX IAC (dev) NSO UBF, LMSAL SOUP MSO GONG, SOHO MDI SWIFT WAMDII
Major Disadvantages Large etalons required, Local finesse variation requires obtaining very good flat fields. Wavefront error, A minimum etalon thickness and minimum FWHM 8pm, High voltages are required Temperature sensitivity, low transmittance, Maximum and minimum calcite elements pushing technology and availability Wavelength range is restricted and multiple wavelength elements are required. Prefilter requirements restricts transmittance
Major Advantages Overall Simplicity, Known technology Working system, Universal filter with the 2pm FWHM, high transmittance Larger FOV than air-gap FPI, Universal filter Large FOV, Universal filter Largest FOV for specified l, Simplicity of operation
Gary, G. A., Balasubrumanium, K. S., 2003,
Additional Notes Concerning the Selection of A
Multiple_Etalon for the Advanced Technology
Solar Telescope.
5
Multiple Imaging Modes

• Imaging spectrograph/spectropolarimeter ( 2pm,
  0.5-1 FOV)
• TESOS, IBIS, NSO Dual FPs
• Imaging Spectro-polarimeter /Imaging
  Magnetograph, (5pm 12pm, 3 FOV)
• UBF/Filter Magnetographs
• Intermediate-band filter (20pm 30pm, 1-3 FOV)
• Dual FP System, UBF-FP combination filters
• Broad-band filter (0.1nm - 2nm, 3FOV)
• Reflection slit-jaw spectroscopy, UBF-like
  spectroscopy

Spectral Coverage 450 750 nm Imaging
Spectrographic Observations
6
Multiple Observational Modes
7
Resolution Spectral Purity

• Single etalon system
• Airy Function, very narrow blocking filter
  (0.2nm)
• for R0.94, minimum transmittance is 10-3 of the
  maximum.
• Multiple etalon system
• Reflectance of coatings, of combined etalons
• Narrow blocking filters (1nm)
• Optimize spectral purity with
• Ratio of Finesse
• Free spectral range
• Design of prefilters
• Triple Etalons have superior out-of-band
  rejection by placement of etalon minima
• Darvaan and Owner-Peterson (1994) Performance
  based on analysis of maximum ghost and SNR

10-4
Reference Gary, G. A., Balasubramaniam, K. S.,
and Sigwarth, M. 2003, Multiple Etalon Systems
for the Advanced Technology Solar Telescope,
SPIE proceeding Innovative Telescopes and
Instruments for Solar Physics, eds. Stephen L.
Keil and Serge V. Avakyan, SPIE 4853-37, p.
252-272.
8
Single vs. Multiple Etalons

• Objective Spectral resolution Dl/l 0.5x10-5
  or 2 pm
• Single etalon system
• Spectral resolution Dl/l l/ F 2 d ,
• F is the finesse and d is the etalon gap
  distance.
• For d1mm, l500nm, Dl/l10-3 /F
• the FSR0.1nm, and narrow FWHM blocking
  filters are required.
• Spectral resolution of 10-5 requires high
  finesse (Fgt100!).
• Multiple etalon system
• Spectral resolution is given by Dl/l FSR / F l
• FSR is the free spectral range of the
  multi-etalons in combination.
• For l500nm, then Dl/l 10-3/FSR , the
• Spectral resolution of 10-5 requires only a
  FSR10nm, hence
• need low finesse of 20 and wide FWHM for the
  blocking filters

9
TESOS Heritage
10
Required Etalon Aperture
n1 (Air/He gap)
n2.1 (liquid gap)
Dl
FOV3
FOV1
x 0.48
200mm
The wavelength variation versus aperture, for 4m
ATST primary with FOV's of 1 and 3. The solid
lines are for l5250Å and the dashed curve is for
l6302Å. For 3 FOV the shift is 120mA for
250mm-aperture (A). For a 1 FOV a 100mm etalon
would allow a reasonable shift of 100mA across
the field of view (B) . The narrow band filter
system in a 100mA mode could do filter
magnetograms. For a spectro-polarimeter with
(20mA) it seems that 150-200mm aperture is
required for 1 FOV (C). Grey Bar F25 realistic
apertures
11
Requirements

• Minimum aperture 200mm diameter
• Wavelength range 450-750nm
• Bi-modal operation - dual and triple system
• Spectral resolution
• 1/250,000 for triple etalon - 50,000 for dual
  etalon
• Minimum Peak Transmission
• 50 (with blocking filters)
• Minimum Peak Transmission
• 10-4
• Maximum Stray-light
• 10-3
• Drift Stability
• 1mÅ/hr

12
TESOS/KIS Optics
13
TESOS/KIS Optical Design
Ghost Suppressors
Cameras
3 or 2 Etalons
Monitors
Motorized
Variable
Focal Plane Reticules, Pinholes Targets, Stops
Laser Source
White Light Imaging, radiance, scaling
Alignment Mask
14
ATST Telecentric Optical Design
15
MFPI 36FOV MODE

• Optical Design Specifications

• Input Beam ATST Coudé F/20
• 200MM Etalons on F/300 Tel. Beam
• 100MM Collimated Beam (Filters)
• WVL Band 450 to 750nm
• 36 FOV Camera Ps1.25/mm
• All Spherical Lenses
• All Spherical Mirrors

Gil Moretto/NSO
16
ATST COUDÉ F/20 MFPI 36FOV MODE
17
MFPI 36FOV MODE LAYOUT
18
TELECENTRICITY
19
MFPI 36FOV CAMERA OPTICAL PERFORMANCE

POLYCHROMATIC
20
Issues

• Determine etalon parameters (d,R,F)
• Detail Darvann-Owner-Peterson-
  Analysis
• Minimize light from parasitic orders
• Emphasizing compatible with operation
  
• actual parameters, electronic
  control, optical setup, drifts
• The final finesse and tunability of the 20cm
  etalons
• Early purchase and test of first (or
  a) 20cm etalon
• Flat fielding problems due to drift
• Atmospheric monitoring and
  correction
• Polarimeter design
• Refine dual camera polarimeter
• Compatibility with multiple mirror
  and nonpolarizing beam
• splitters and ATST Mueller matrix

21
Issues

• Spatial reflection ghost
• Tilt, wedge angles, calibration,
  optical testing at
• TESOS
• Determine building strategy
• Full or partial construction,
  prefilter set
• Refine estimated cost
• Updated pricing and cost analysis
• Telecentric beam/ Collimated Option
• F/250 at FPIs
• Detail pupil apodization analysis
• Complexities of off-axis optical systems
• Detail optical ray tracing and
  analysis
• Polarization study and Coude focus

22
Technology Studies

• Laura Allaire (Ph.D. student) in Optics at the
  University of Rochester is centering her thesis
  work on multiple Fabry-Perot interferometry and
  will assist in the ATST MFPI design. She started
  this summer (2003).
• Gil Moretto/NSO will continue to improve the
  breadboard design of the ATST MFPI.
• Ghost, apodization,and general concerns listed
  above will continue to be studied. (Allaire/UR)
• A second observational run at TESOS will
  hopefully provide a more through understanding of
  their instrument (e.g. ghost, drift, and spectral
  resolution). Thomas Kentischer/KIS is active
  member of the team.
• An improved cost estimate will be developed (lens
  vs mirrror)
• Alternate concepts will be explored, e.g. dual
  etalons, as first light configuration
• Flexible optical design to be considered to allow
  for advancement in technology.

23
Cost estimate (preliminary)

• Engineering design.... 1,200,000
• Optical, Mechanical, ElectronicEngineer
  s and Scientist-Project Manager for 2 years each
• Optical elements. 21,000
• Mechanical elements. 12,000
• Electronic elements 140,000
• Three 20cm etalons 834,000
• Commercial software .... 4,000
• Electronic and computer Interface....
  175,000
• Assembly, test, integration 300,000
• Optical, Mechanical, Electronic-Engineer
  s and Scientist-Project Manager for 1/2 years
  each
• 
  Total 2,686,000

24
ATST Science

• The imaging filter system for the ATST will
  provide the observational opportunities to
  spectrally probe the magnetic and hydrodynamic
  fine structures of the photosphere and the
  chromosphere at ultra-high spatial resolution.
• This filter will possess high-transmittance, and
  allow instantaneous, narrow-band spectral
  observations over an extended area of the Sun.
• The observations will allow rapid 3D-imaging
  spectrometry, Stokes spectropolarimetry, accurate
  surface photometry, and provide spectroheliograms
  that will measure Doppler velocity, transverse
  flows, and allow feature tracking, and the study
  of evolutionary changes of solar activity. When
  incorporated with the adaptive optics (AO)
  system, (with added optical correction techniques
  such as speckle interferometry), focal-volume and
  other post-focal techniques will allow finer
  spatio-spectral analysis.
• Narrow-band spectral imagery offers the advantage
  of avoiding spectrograph rasterization, with a
  distinct disadvantage of sequential tuning but
  its high throughput and resultant cadence,
  coupled with active and adaptive optics
  corrections provide a good mitigation for this
  disadvantage.
• Provide one of the core instruments in multiple
  instrument mode of observing solar phenomena.

25
Summary

• Multiple-Filter Modes
• Narrow Passband Spectral Power 250,000 (2pm)
• Throughput 50 (goal)
• Field of View 1-3 arcmin (mode dependent)
• Wavelength Coverage 450-750 nm
• Dual Camera Polarimetry
• Spectral Purity Parasitic peaks lt 10-4
• Existing Technology

26
References

• Gary, G. A., Balasubramaniam, K. S., Sigwarth,
  M. 2003, Multiple-etalon Systems for the
  Advanced Technology Solar Telescope, Innovative
  Telescopes and Instrumentation for Solar
  Astrophysics, eds. S. L. Keil and S. V. Avakyan,
  SPIE Proceedings 4853, 252.
• Gary, G. A., Balasubramaniam, K. S., Sigwarth,
  M. 2003, Additional Notes Concerning the
  Selection of a Multiple-Etalon System for the
  Advanced Technology Solar Telescope, Internal
  ATST document (currently)
• Kentischer, T., Sigwarth, M., Schmidt, W., and v.
  Uexkull, M. 1998, TESOS-Telecentric Etalon
  Solar Spectrometer, TB v1.0, Kiepenheuer
  Institut fur Sonnenphysik, Freiburg, Germany.
• Kentischer, T., Sigwarth, M., Schmidt, W., and v.
  Uexkull, M. 1998, "TESOS, a double Fabry-Perot
  instrument for solar spectroscopy", AA, 340,
  569.
• Langhans, K. Schmidt, W. Tritschler, A.,
  2002,2D-spectroscopic observations of G-band
  bright structures in the solar photosphere,
  Astronomy and Astrophysics, 394, 1069.
• Tritschler, A. Schmidt, W. Langhans, K.
  Kentischer, T., 2002,High-resolution solar
  spectroscopy with TESOS - Upgrade from a double
  to a triple system, Solar Physics, 211, 17.
• von der Lühe, O. and Kentischer, Th. J. 2000,
  High Spatial Resolution of a Triple Fabry-Perot
  Filtergraph,Astron. Astrophys. Suppl. Ser., 146,
  499.