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Tunable filter wavelength scan and calibration of intensity ripple

Detailed analysis of wavelength scans and intensity ripple calibration for spectroscopic performance verification. Solar spectrum and lamp source data sets used. Improvement of spectrum line profiles post calibration.

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Tunable filter wavelength scan and calibration of intensity ripple

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  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.

  11. 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; del=0.1l, halfwave-3; del=0.05l, 5250A

  12. 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 biare derived by fitting of the intensity profiles at each position in FOV.

  13. 5250A amplitude and phase distribution @ T21C Phase Amplitude Calcite-6 Amplitude Phase Calcite-3

  14. 5250A amplitude and phase distribution @ 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

  16. 6302A amplitude and phase distribution Phase Amplitude Calcite-3 Phase Amplitude Calcite-5 Phase Amplitude Calcite-6

  17. 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

  18. 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

  19. 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

  20. 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

  22. 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.

  23. Broadband Filter Imager (1) CN bandhead Center: 388.35nm FWHM: 0.7nm Ca II H Center: 396.85nm FWHM: 0.3nm

  24. Broadband Filter Imager (2) G-band Center: 430.50nm FWHM: 0.8nm Blue continuum Center: 450.55nm FWHM: 0.4nm

  25. Broadband Filter Imager (3) Green continuum Center: 555.05nm FWHM: 0.4nm Red continuum Center: 668.40nm FWHM: 0.4nm

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