Imaging,Visible, Tunable, Imaging,Visible, Tunable, Narrow- Passband Passband Filter System 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
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Imaging,Visible, Tunable, Passband Filter System Imaging,Visible, Tunable, Narrow-Passband Filter System A Multiple Fabry-Perot Etalon Interferometer for.
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Imaging,Visible, Tunable, Imaging,Visible, Tunable, Narrow-Passband Passband Filter SystemFilter 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
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
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)
Comparison with other alternativesATST VisibleNarrow-Band Filter
KIS TESOS, USAF ISOON,ItalianUBI, Sac Peak Dual FPI
Flare Genesis,Mees UHIMaX IAC (dev)
NSO UBF,LMSAL SOUP
MSO GONG,SOHO MDISWIFT WAMDII
MajorDisadvantages
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
MajorAdvantages
Overall Simplicity,Known technologyWorking 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 ,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 .
• Single etalon system– Airy Function, very narrow
blocking filter (~0.2nm)– for R=0.94, 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
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.
10-4
Single vs. Multiple Etalons
Objective: Spectral resolution = ~ 0.5x10-5 or 2 pm
• Single etalon system– Spectral resolution: ~ F 2 d
– F is the finesse and d is the etalon gap distance. – For d~1mm, =500nm, ~10-3 /F; the FSR=0.1nm, and narrow FWHM blocking filters are
required. Spectral resolution of 10-5 requires high finesse (F>100!).
• Multiple etalon system – Spectral resolution is given by~ FSR / F
– FSR is the free spectral range of the multi-etalons in combination.
– For =500nm, then ~ 10-3FSR , the Spectral resolution of 10-5 requires only a FSR~10nm, hence need low finesse of 20 and wide FWHM for the blocking filters
TESOS Heritage
AB
C
Required Etalon Aperture
The wavelength variation versus aperture, for 4m ATST primary with FOV's of 1 and 3’. The solid lines are for 5250Å and the dashed curve is for 6302Å. 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: F~25 realistic apertures
• Complexities of off-axis optical systems Detail optical ray tracing and analysis Polarization study and Coude focus
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.
Cost estimate (preliminary)
• Engineering design…………………....$ 1,200,000• [Optical, Mechanical, Electronic–Engineers 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-Engineers and
Scientist-Project Manager for 1/2 years each]• Total…… $2,686,000
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.
• Throughput: 50% (goal)• Field of View: 1-3 arcmin (mode dependent)• Wavelength Coverage: 450-750 nm • Dual Camera Polarimetry• Spectral Purity: Parasitic peaks < 10-4
• Existing Technology
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", A&A, 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.