Tunable filter wavelength scan and calibration of intensity ripple

1
Tunable filter wavelength scan and calibration
of intensity ripple

• Y. Katsukawa (NAOJ) and SOT team

2
TF wavelength scan

• Wavelength scan by the tunable filter was
  performed to verify spectroscopic performance and
  its uniformity over the field-of-view.
• Two data sets
• Solar spectra to check spectrum line profiles and
  their uniformity
• Lamp source (emitting continuum light) to check
  intensity variation through the scan
• Each full FOV image is divided into 8x4
  sub-images, and spectrum is created in each
  sub-image.

3
Wavelength scan of the solar spectrum lines (1)
Mg I 5172A
Fe I 5250A
Black Measured spectra Red Atlas TF ideal
profiles
4
Wavelength scan of the solar spectrum lines (2)
Fe I 5576A
Na I 5896A
Black Measured spectra Red Atlas TF ideal
profiles
5
Wavelength scan of the solar spectrum lines (3)
Fe I 6302A
H I 6563A
Black Measured spectra Red Atlas TF ideal
profiles
6
Solar spectra by NFI

• These data sets show the line profiles are
  roughly consistent with the atlas spectra, and
  roughly uniform over the FOV.
• Two features can be seen in the spectra
• 1. Periodic intensity variation, especially
  significant in 5250A.
• 2. The line profiles are slightly shallower than
  the atlas spectra.
• In order to distinguish the solar spectrum
  features and intensity variation caused by the
  instrument, wavelength scans were carried out
  using a lamp source emitting continuum light.

7
Wavelength scan of a lamp source (1)
Mg I 5172A
Fe I 5250A
Black Measured intensity Red Fitting result
8
Wavelength scan of a lamp source (2)
Fe I 5576A
Na I 5896A
Black Measured intensity Red Fitting result
9
Wavelength scan of a lamp source (3)
Fe I 6302A
H I 6563A
Black Measured intensity Red Fitting result
10
Intensity ripple in TF wavelength scan

• Amplitudes of the ripple are around 10 20 ,
  and are position dependent over FOV. They are
  also dependent on wavelengths.
• Periodic variation is dominant in 5172A and
  5250A. We found two periods are dominant in the
  ripples.
• For the longer wavelengths, the ripple profiles
  are more complex. Many periods may be superposed.

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Model of the intensity ripple

• TF consists of 8 calcite blocks and 8 tuning
  elements (motors). Each calcite block has a
  halfwave plate in the middle of the block to make
  wide fields.
• The tuning elements move periodically through the
  scan, and their periods are different from each
  other.
• The intensity ripple can be reproduced by giving
  errors to retardation of the halfwave plates in
  the calcite blocks 3 and 6.

halfwave-6 del0.1l, halfwave-3 del0.05l,
5250A
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Calibration of the intensity ripple

• If the intensity ripple is caused by the halfwave
  plates in the calcite blocks, the intensity
  modulation can be represented as a function of
  the motor positions (provided by encoders) of the
  tuning elements.

Motor positions corresponding to ith calcite
block
Intensity amplitude for ith calcite block
(Position dependent)
Phase of the motor position for ith calcite
block (Position dependent)
ai and bi are derived by fitting of the intensity
profiles at each position in FOV.
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5250A amplitude and phase distribution _at_ T?21?C
Phase
Amplitude
Calcite-6
Amplitude
Phase
Calcite-3
14
5250A amplitude and phase distribution _at_ T?25?C
Phase
Amplitude
Calcite-6
Amplitude
Phase
Calcite-3
The amplitude and phase are almost the same as
those at T?21?C.
15
Spectra after calibration of I-ripple 5250A
Fe I 5250A
Black Measured Red Atlas TF ideal profiles
Black After corrected Red Atlas TF ideal
profiles
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6302A amplitude and phase distribution
Phase
Amplitude
Calcite-3
Phase
Amplitude
Calcite-5
Phase
Amplitude
Calcite-6
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Spectra after calibration of I-ripple 6302A
Fe I 6302A
Black Measured Red Atlas TF ideal profiles
Black After corrected Red Atlas TF ideal
profiles
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Spectra after calibration of I-ripple 5576A
Fe I 5576A
Black Measured Red Atlas TF ideal profiles
Black After corrected Red Atlas TF ideal
profiles
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Spectra after calibration of I-ripple 5172A
Mg I 5172A
Black Measured Red Atlas TF ideal profiles
Black After corrected Red Atlas TF ideal
profiles
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Spectra after calibration of I-ripple 5896A
Na I 5896A
Black Measured Red Atlas TF ideal profiles
Black After corrected Red Atlas TF ideal
profiles
21
Spectra after calibration of I-ripple 6563A
H I 6563A
Black Measured Red Atlas TF ideal profiles
Black After corrected Red Atlas TF ideal
profiles
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Summary

• On orbit, the ripple patterns move with respect
  to the solar spectrum lines because the satellite
  Doppler motion and temperature changes in TF. But
  we can calibrate them because they are the
  patterns fixed to the motor positions.
• The spectrum line profiles are significantly
  improved by the calibration of the intensity
  ripple using the motor positions of the tuning
  elements.
• Similar wavelength scan data will be obtained at
  times in flight in order to verify tuning
  accuracy and the calibration function (amplitude
  and phase distribution) of the intensity ripple.

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Broadband Filter Imager (1)
CN bandhead Center 388.35nm FWHM 0.7nm
Ca II H Center 396.85nm FWHM 0.3nm
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Broadband Filter Imager (2)
G-band Center 430.50nm FWHM 0.8nm
Blue continuum Center 450.55nm FWHM 0.4nm
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Broadband Filter Imager (3)
Green continuum Center 555.05nm FWHM 0.4nm
Red continuum Center 668.40nm FWHM 0.4nm