Near Infrared Tunable Filter System
for ATST
Aug. 25, 2003
Big Bear Solar Observatory &
Solar Research Center, NJIT
NIR Tunable Filter System
CCD1
Polarization
Analyzer
Prefilter
Lyot-filter
FP
CCD2
Design Requirements
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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
Operation Mode I - Narrow passband
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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
Operation Mode II - Medium passband
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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
Operation Mode III - Broad passband
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Configuration: Interference Filters
Passband FWHM: 20~50Å
FOV: ~ 1-3 arcmin
Observation Mode: Active Region Evolution and
Morphology Analysis
• Peak Transmission: >80%
Instrument I — NIR Lyot Filter
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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
Sketch of the NIR Tunable Birefringent Filter
C
P
C
½ ¼
½
½
P

C
½
C
½ C C½
¼ P

C ½ C ¼ P ½ ¼ P


P: Polarizer. C: Calcite. ½: Half waveplate. ¼: Quarter waveplate.
T  cos 2 (
d1
2 d1
2 d1
2 d1


2

)

cos
(


2

)

cos
(


2

)

cos
( 3   2 4 )
1
2
3
0
1
2
2
2
2
2
d1 is the thickness of the thickest calcite, i is the rotated angle of the rotating half
waveplates,  is the birefrinegent index of calcite,  is wavelength.
Research on the FOV of Birefringent Filter
Wavelength
(m)
Module I
0.05Å
shifting
0.1Å
shifting
Module II
0.05Å
shifting
0.1Å
shifting
Module III
0.05Å
shifting
0.1Å
shifting
Module IV
0.05Å
shifting
0.1Å
shifting
1.042
1 01
1 27
1 27
2 03
2 03
2 54
2 54
4 06
1.097
1 00
1 26
1 26
2 02
2 02
2 52
2 52
4 04
1.159
1 01
1 26
1 26
2 02
2 02
2 53
2 53
4 05
1.220
1 01
1 26
1 26
2 02
2 02
2 53
2 53
4 04
1.273
1 00
1 25
1 25
2 00
2 00
2 52
2 52
4 03
1.307
1 00
1 25
1 25
2 01
2 01
2 51
2 51
4 00
1.497
1 00
1 25
1 25
2 01
2 01
2 51
2 51
4 01
1.541
1 00
1 25
1 25
2 01
2 01
2 51
2 51
4 01
1.609
1 00
1 25
1 25
2 01
2 01
2 51
2 51
4 01
1.682
1 00
1 25
1 25
2 01
2 01
2 51
2 51
4 01
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.
Instrument II — NIR Fabry-Perot
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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
Instrument III — CCD Cameras
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
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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%
Progress
• Design of achromatic waveplates from 1.0 to 1.7m
An example of 3-component achromatic half-waveplate design in NIR
Achromatic Range: 1.0 to 1.7 m
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.
Progress
• Measurement of birefringent index of calcite from 1.0 to 1.7m
-0.150
Bire fringe nt Inde x
-0.155
-0.160
-0.165
-0.170
-0.175
-0.180
-0.185
-0.190
0.40
0.60
0.80
1.00
1.20
1.40
1.60
1.80
Wavelength(micron)
Comparison of the values of birefringent index  in the literature with the
measured values. Diamond: values in the literature, triangle: measured values.
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
External Requirement
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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.
………..
On Going…...
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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
Thank You !