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Near Infrared Tunable Filter System for ATST

Near Infrared Tunable Filter System for ATST. Big Bear Solar Observatory & Solar Research Center, NJIT. Aug. 25, 2003. NIR Tunable Filter System. CCD1. Polarization Analyzer. FP. CCD2. Prefilter. Lyot-filter. Design Requirements. Spectral coverage: 1.0~1.7 m Resolving power: 150,000

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Near Infrared Tunable Filter System for ATST

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  1. Near Infrared Tunable Filter System for ATST Big Bear Solar Observatory & Solar Research Center, NJIT Aug. 25, 2003

  2. NIR Tunable Filter System CCD1 Polarization Analyzer FP CCD2 Prefilter Lyot-filter

  3. Design Requirements • Spectral coverage: 1.0~1.7m • Resolving power: 150,000 • FOV: 1~3 arcmin • Bandpass: ~ 0.1Å • Spatial resolution: ~ 0.1 arcsec • Multi-operation: narrow, medium, and broad • Filter aperture: Lyot filter~36mm, FP~150mm • Tunable range 1.0~1.7m • High optical quality • High throughput: ~40% for polarized light • Stray light: ~ 10-3 • Stability: ~ 0.05Å/hour

  4. Operation Mode I - Narrow passband • Configuration: Interference Filters + Lyot Filter + NIR FP • Passband FWHM: 0.1Å • FOV: ~ 1 arcmin • Observation Mode: Imaging Spectrograph / Spectropolarimetry • Interested Lines: FeI 11607.6, 11783.3, 11882.8, 11884.1, 12879.8, 15207.5, 15219.6, 15245.0, FeI 15648.5, 15652.9, 1566.0, 15723.6 H 12818, Cont 16300 HeI 10830.34, 10830.25, 10829.08 CI 10683.1, 10685.4, 10691.2, 10729.5 MgII: 10952, 10914, FeXIII 10747, 10798 CN at J-band, OH at H-band: OH 15422.4, 15419.6, 15409.3, 15407.4 • Peak Transmission: ~40% for polarized light

  5. Operation Mode II - Medium passband • Configuration: Interference Filters + Lyot Filter • Passband FWHM: 2~3Å • FOV: ~ 1-3 arcmin • Observation Mode: Filtergram • Interesting Spectral Lines: FeI 15648.5, 15652.4 HeI 10830.34, 10830.25, 10829.08 Continuum 1.63m H (P) 12818 CN at J-band, OH at H-band • Peak Transmission: ~ 40% for polarized light

  6. Operation Mode III - Broad passband • Configuration: Interference Filters • Passband FWHM: 20~50Å • FOV: ~ 1-3 arcmin • Observation Mode: Active Region Evolution and Morphology Analysis • Peak Transmission: >80%

  7. Instrument I — NIR Lyot Filter • Tunable ability: 1.0~1.7 m • Clear Aperture: ~ 36 mm • Bandpass FWHM: 2.5 ~ 3.0 Å • Peak Transmission: ~ 40% for polarized light • Internal Structure: 3-module or 4-module • Temperature Controller: 45 ± 0.05°C • Achromatic Components: waveplates, polarizers • Wavelength Tuning Methods: I.Calcite + 1/4 waveplate + Rotating 1/2 waveplate II.Calcite + LC variable retarder

  8. C C ½ ½ ½ C C ½ P ½ ¼ P C ½ C ¼ P C ½ C ¼ P ½ ¼ P     Sketch of the NIR Tunable Birefringent Filter P: Polarizer. C: Calcite. ½: Half waveplate. ¼: Quarter waveplate. d1 is the thickness of the thickest calcite, iis the rotated angle of the rotating half waveplates,  is the birefrinegent index of calcite,  is wavelength.

  9. Research on the FOV of Birefringent Filter The FOV allowed for 0.05Å and 0.1Å Shifting of Passband Compared to the FWHM (2.4 Å) of each module of IR Lyot Filter, these shifting are negligible.

  10. Instrument II — NIR Fabry-Perot • Tuning Range: 1.0~1.7 m • Clear Aperture: ~ 150 mm • Bandpass FWHM: ~ 0.1 Å @ 15648 Å • Peak Transmission: > 90% • Effective Finesse: ~ 60 • FOV: ~ 1 arcmin for spectropolarimeter

  11. NIR camera(CCD2) Candidate: HgCdTe & InGaAs Format: 10241024 A/D: 14 bit or 16 bit Readout: 4 quadrant output Fill factor: 100% FOV: 60 diffraction limit 0.1@1.56m sampling 0.058 QE: > 60% LN2 Cooling Visible camera(CCD1) for image alignment Si CCD Format: 20482048 A/D: 14 bit or 16 bit Readout: frame transfer Fill factor: 100% FOV: 60 diffraction limit 0.03@5000Å sampling 0.029 QE: >1% Instrument III — CCD Cameras

  12. Progress • Design of achromatic waveplates from1.0 to 1.7m An example of 3-component achromatic half-waveplate design in NIR Achromatic Range: 1.0 to 1.7 m

  13. Progress 15648Å 10830Å Single Waveplate Retardation Variance Compared to single Waveplate, the new design is practically “achromatic”. The threshold of retardation variance is set to be 1% of the final retardation. This is basically the limit of machinery sensitivity.

  14. Progress • Measurement of birefringent index of calcite from 1.0 to 1.7m Comparison of the values of birefringent index  in the literature with the measured values. Diamond: values in the literature, triangle: measured values.

  15. Progress • 3-module design of Lyot filter to increase transmission 3-module detailed Lyot filter transmission at FeI 1.5648 m Sidelobe contamination for 3-module is ~0.54%, compared with 0.40% for 4-module; transmission increase by21% from 37% to 45% for polarized light

  16. External Requirement • Room temperature control. • Pressure and vibration monitoring and controlling. • Frequency stabilized infrared laser source. • Polarization modulator system handshake. • Telescope control system handshake. • CCD cameras capture system control. • AO system on-off control. • ………..

  17. On Going…... • Simulation of match between Lyot filter and Fabry-Perot • Experiment of liquid crystal variable retarder • Design of near infrared polarization analyzer • Calculation of ghost image of near infrared filter system • Consideration of dual near infrared Fabry-Perot system • Study of stability and repeatability of NIR Fabry-Perot • Optical design for NIR tunable filter system • Optimization of NIR tunable filter system

  18. Thank You !

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