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Design and Application of Near Infrared Tunable Filter for ATST and NST Doctoral Thesis Proposal by Jun Ma February, 2005. Contents. Introduction Related Work Achromatic Waveplate Layered medium Infrared Imaging Magnetograph system (IRIM)
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FTS Observation of umbral Stokes profiles: I & V.
Field Strength is roughly around 300 Gauss.
Rueedi, et al., 1994
Big Bear Solar Observatory
A substitution of current 65cm telescope. It will be the largest ground based solar telescope before the construction of ATST (2006).
Advanced Technology Solar Telescope (ATST)
National Solar Observatory
Based on the theoretical models, the magnetic features on the Sun have spatial scales about 30km. This corresponds to a 4-meter aperture at 630.2 nm, an important line for most polarimetry studies.
Lift time spans 3~4 decades.
My thesis project is supported by ATST “near infrared tunable filter system” project.
Polarization Modulation (one example):
Baur & Elmore, “Stokes II – A new polarimeter for solar observation”, 1980
1.56 m Birefringent filter, designed by Dr. J. Wang.
Bandpass = 2.2 Å ; LC tuning; normal-wavelates.
Used in the observation at SacPeark, in Dec. 2004
Tunable Laser testing of 1.56m birefringent filter.
Proceeded at Cambridge Research Incorporated (CRi),
Tunable Birefringent Filter design in J. Wang’s paper. without achromatism consideration, i.e., working at single wavelength.
Wavelength tuning v.s. rotation angle of waveplate
A linear relation.
Simulated with Jones matrix method in MATLAB.
Voltage count on LC’s v.s. retardation
[Courtesy CRi, Inc.]
Non-linear; oracle function
How about different layers of different birefringent materials?
How many do we need?
[ Left Panel ] Retardance error plotted from Title’s paper.
1975 – A.M. Title, “Improvement of Birefringent Filters 2: Achromatic Waveplates”, J.O.S.A., 1975
[ Right Panel ] Retardance error plotted from new design.
2004 – J. Ma, J. Wang, W. Cao, C. Denker, H. Wang. “Near Infrared (NIR) Achromatic Phase Retarder”, SPIE, Oct 2004
Transmission profile (not retardance profile). Courtesy Nanjing Institution of Astronomical Instrumentation.
1) Half awp sandwiched by parallel aligned linear polarizers
2) Two quarter awp sandwiched by parallel aligned linear polarizers
Blue curve: achromatic waveplate
Red curve: normal waveplate
Yellow curve: stray light of the two linear polarizers
Calibration of 1.56 micron Lyot filter from data of December, 2004.
FWHM ~ 2.1 angstrom
(6) Light Bridges and Umbral Dots
[ Dec. 2, 2004, NSO-SacPeak ]
FOV: 120” 120”
Filtergram observed @ 1.56 m
FWHM = 2.2 Å
Processed with flat-field correction. The dynamic process of these two interests me more. How do they evolve?
Lyot + FPI
Centred at 1.56 micron
Bandwidth ~0.15 angstrom
Seeing condition got worse during this period compared with the observation with Lyot filter one day before.
The fringe pattern comes probably from FPI, since it didn’t appear in Lyot observation. However, it could come from other optics as well, since the optical setup were quite different.
Again, a movie might be more interesting. Also, since the filter system was used to scan the neighbouring spectral range, the Zeeman splitting of the FeI line might be derived from this time sequence of images. Data process hasn’t been done yet.