Near Infrared Tunable Filter System for ATST

Big Bear Solar Observatory &

Solar Research Center, NJIT

Aug. 25, 2003

NIR Tunable Filter System

CCD1

CCD2

Prefilter Lyot-filter

FPPolarizationAnalyzer

Design Requirements

• Spectral coverage: 1.0~1.7m• 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 1.0~1.7m• High optical quality• High throughput: ~40% for polarized light• Stray light: ~ 10-3

• Stability: ~ 0.05Å/hour

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, 15723.6H 12818, Cont 16300HeI 10830.34, 10830.25, 10829.08CI 10683.1, 10685.4, 10691.2, 10729.5MgII: 10952, 10914, FeXIII 10747, 10798CN at J-band, OH at H-band: OH 15422.4, 15419.6, 15409.3, 15407.4

• Peak Transmission: ~40% for polarized light

• 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 1.63m

H (P) 12818

CN at J-band, OH at H-band• Peak Transmission: ~ 40% for polarized light

Operation Mode II - Medium passband

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%

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

Sketch of the NIR Tunable Birefringent Filter

)22

(cos)22

(cos)22

(cos)22

(cos 4312

3212

2112

1012

dddd

T

P: Polarizer. C: Calcite. ½: Half waveplate. ¼: Quarter waveplate.

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.

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

Research on the FOV of Birefringent Filter

Wavelength

(m)

Module I Module II Module III Module IV

0.05Å

shifting

0.1Å

shifting

0.05Å

shifting

0.1Å

shifting

0.05Å

shifting

0.1Å

shifting

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

• 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: 10241024• A/D: 14 bit or 16 bit• Readout: 4 quadrant output• Fill factor: 100%• FOV: 60 diffraction limit 0.1@1.56m

sampling 0.058• QE: > 60%• LN2 Cooling

Visible camera(CCD1)for image alignment

• Si CCD• Format: 20482048• A/D: 14 bit or 16 bit• Readout: frame transfer• Fill factor: 100%• FOV: 60 diffraction limit

0.03@5000Åsampling 0.029

• QE: >1%

Progress

• Design of achromatic waveplates from 1.0 to 1.7m

An example of 3-component achromatic half-waveplate design in NIRAchromatic Range: 1.0 to 1.7 m

Progress

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.

Retardation Variance

15648Å10830Å

Single Waveplate

Progress

• Measurement of birefringent index of calcite from 1.0 to 1.7m

-0.190

-0.185

-0.180

-0.175

-0.170

-0.165

-0.160

-0.155

-0.150

0.40 0.60 0.80 1.00 1.20 1.40 1.60 1.80

Wavelength(micron)

Bire

frin

gent

Inde

x

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 mSidelobe 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

• 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…...

• 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 !