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Design Requirements. Spectral coverage: 1.0~1.7?mResolving power: 150,000FOV: 1~3 arcminBandpass: ~ 0.1Spatial resolution: ~ 0.1 arcsecMulti-operation: narrow, medium, and broadFilter aperture: Lyot filter~36mm, FP~150mmTunable range 1.0~1.7?mHigh optical qualityHigh throughput: ~40% for p
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1. Near Infrared Tunable Filter System for ATSTHaimin Wang Solar Research Center
New Jersey Institute of Technology Today, I would like to show you some up-to-date progress about the near
infrared tunable filter(NIRTF) for ATST, including design requirements of the
infrared filter system, operation modes, the designs of infrared Lyot filter,
infrared Fabry-Perot, and detectors. In addition, some ongoing researches and
the requirements to external instruments and modules are introduced also.Today, I would like to show you some up-to-date progress about the near
infrared tunable filter(NIRTF) for ATST, including design requirements of the
infrared filter system, operation modes, the designs of infrared Lyot filter,
infrared Fabry-Perot, and detectors. In addition, some ongoing researches and
the requirements to external instruments and modules are introduced also.
2. Design Requirements Spectral coverage: 1.0~1.7?m
Resolving power: 150,000
FOV: 1~3 arcmin
Bandpass: ~ 0.1Ĺ
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: ~ 0.05Ĺ/hour According to the scientific objectives of ATST, we provide the design
requirements of this near infrared tunable filter for ATST. It should be mentioned
that it is a preliminary version. Some design parameters are possible to be revised.
Spectral coverage: 1.0~1.7 ?m, span about 7000 angstrom, and that can cover
two near infrared atmosphere windows: J(1.2 ?m)? and H(1.6 ?m). For the rest
two spectral bands in the near infrared K(2.2 ?m) and L(3.4 ?m), the filters need
the different designs.
Resolving power&Bandpass: the current design is sufficient to detect the full
range of line profile features in the near infrared. The wavelength sampling (10~
30steps)is dense enough to research radiative-transfer based Stokes inversion
techniques.
Multi-operation mode: for the different observation objects, we design three
operation mode: narrow passband, medium passband, and broad passband.
FOV: 1~3 according to different operation mode.
Spatial resolution~0.1, which is the diffraction limit of 4m telescope in NIR.
Throughput: for the polarized light and 3-module of Lyot filter, ~40%According to the scientific objectives of ATST, we provide the design
requirements of this near infrared tunable filter for ATST. It should be mentioned
that it is a preliminary version. Some design parameters are possible to be revised.
Spectral coverage: 1.0~1.7 ?m, span about 7000 angstrom, and that can cover
two near infrared atmosphere windows: J(1.2 ?m)? and H(1.6 ?m). For the rest
two spectral bands in the near infrared K(2.2 ?m) and L(3.4 ?m), the filters need
the different designs.
Resolving power&Bandpass: the current design is sufficient to detect the full
range of line profile features in the near infrared. The wavelength sampling (10~
30steps)is dense enough to research radiative-transfer based Stokes inversion
techniques.
Multi-operation mode: for the different observation objects, we design three
operation mode: narrow passband, medium passband, and broad passband.
FOV: 1~3 according to different operation mode.
Spatial resolution~0.1, which is the diffraction limit of 4m telescope in NIR.
Throughput: for the polarized light and 3-module of Lyot filter, ~40%
3. Operation Mode I - Narrow passband Configuration: Interference Filters + Lyot Filter + NIR FP
Passband FWHM: 0.1Ĺ
FOV: ~ 1 arcmin
Observation Mode: Imaging Spectrograph / Spectropolarimetry
Interesting Spectral 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 As mentioned above, there are 3 observation modes for this IR tunable filter.
The first mode is narrow passband operation mode. Passband FWHM ~ 0.1
angstrom. The optical configuration adopts interference filters + Lyot filter +
near infrared Fabry-Perot. This mode is mainly used as the imaging spectrograph,
imaging spectropolarimetry or vector magnetogram. For the 4m aperture and a
full FOV of 3, we would require an etalon aperture of >500mm. It exceeds
manufacturing ability largely. So, in order to keep ~0.1angstrom passband, FOV~1
and 150mm aperture FP is a good choice.
{Calculation method: For a collimated-mounted
etalon, wavelength shift through an etalon is ~?2?/2(? is maximum incident angle);
For a telecentric-mount etalon, effective bandpass is ~[(fwhm)2+(?2?/2)2]1/2.
According to the Lagrange optical invariant, ?=Datst/Dfp*FOVatst/2.}
Many interesting spectral lines can be observed in this operation mode.
FeI 15648/15652 pair: plage, umbra, network and intranetwork magnetic field;
HeI 10830: chromosphere magnetic field, corona hole
..;
Many strong stokes Q and V atomic lines to probe weak magnetic field...;
Infrared molecular lines with high temperature sensitivity
.;
Cont. 1.6?m: the deepest layer of photosphere
.;As mentioned above, there are 3 observation modes for this IR tunable filter.
The first mode is narrow passband operation mode. Passband FWHM ~ 0.1
angstrom. The optical configuration adopts interference filters + Lyot filter +
near infrared Fabry-Perot. This mode is mainly used as the imaging spectrograph,
imaging spectropolarimetry or vector magnetogram. For the 4m aperture and a
full FOV of 3, we would require an etalon aperture of >500mm. It exceeds
manufacturing ability largely. So, in order to keep ~0.1angstrom passband, FOV~1
and 150mm aperture FP is a good choice.
{Calculation method: For a collimated-mounted
etalon, wavelength shift through an etalon is ~?2?/2(? is maximum incident angle);
For a telecentric-mount etalon, effective bandpass is ~[(fwhm)2+(?2?/2)2]1/2.
According to the Lagrange optical invariant, ?=Datst/Dfp*FOVatst/2.}
Many interesting spectral lines can be observed in this operation mode.
FeI 15648/15652 pair: plage, umbra, network and intranetwork magnetic field;
HeI 10830: chromosphere magnetic field, corona hole
..;
Many strong stokes Q and V atomic lines to probe weak magnetic field...;
Infrared molecular lines with high temperature sensitivity
.;
Cont. 1.6?m: the deepest layer of photosphere
.;
4. Configuration: Interference Filters + Lyot Filter
Passband FWHM: 2~3Ĺ
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 II - Medium passband The second operation observation configuration is medium passband mode.
Under this mode, interference filters and Lyot tunable filter are used to acquire
2~3 angstrom passband. Observation mode are the filtergrams
and filter vetor magnetograms. Field of view is ~1-3. For the polarized light,
peak transmission can reach 40%.
The second operation observation configuration is medium passband mode.
Under this mode, interference filters and Lyot tunable filter are used to acquire
2~3 angstrom passband. Observation mode are the filtergrams
and filter vetor magnetograms. Field of view is ~1-3. For the polarized light,
peak transmission can reach 40%.
5. Operation Mode III - Broad passband Configuration: Interference Filters
Passband FWHM: 20~50Ĺ
FOV: ~ 1-3 arcmin
Observation Mode: Active Region Evolution and Morphology Analysis
Peak Transmission: >80% The last operation configuration is broad passband mode. Infrared interference
filters are used to provide 20~50 angstrom passband as the research and
observation of active region evolution and morphology analysis. Under this
mode, peak transmission can reach >80%.The last operation configuration is broad passband mode. Infrared interference
filters are used to provide 20~50 angstrom passband as the research and
observation of active region evolution and morphology analysis. Under this
mode, peak transmission can reach >80%.
6. NIR Tunable Filter System Here is the schematic optical path of near infrared tunable filter system for the
narrow passband operation mode.
The light from ATST telescope is split into two beams by a light splitting. One
beam is fed into CCD1 as reference white-light images. Another beam is fed into
the infrared tunable filter system, polarization analyzer. The monochromatic or
polarization images are captured by an infrared camera(CCD2). Every component
in optical path can be moved out easily to fulfill the different observation
operation mode.
I will discuss every instrument in detail.Here is the schematic optical path of near infrared tunable filter system for the
narrow passband operation mode.
The light from ATST telescope is split into two beams by a light splitting. One
beam is fed into CCD1 as reference white-light images. Another beam is fed into
the infrared tunable filter system, polarization analyzer. The monochromatic or
polarization images are captured by an infrared camera(CCD2). Every component
in optical path can be moved out easily to fulfill the different observation
operation mode.
I will discuss every instrument in detail.
7. Instrument I NIR Lyot Filter Tunable ability: 1.0~1.7 ?m
Clear Aperture: ~ 36 mm
Bandpass FWHM: 2.5 ~ 3.0 Ĺ
Peak Transmission: ~ 40% for polarized light
Internal Structure: 3-module or 4-module
Temperature Controller: 45 ą 0.05°C
Achromatic Components: waveplates, polarizers
Wavelength Tunable Methods:
I. Calcite + 1/4 waveplate + Rotating 1/2 waveplate
II. Calcite + LC variable retarder As the prefilter of Fabry-Perot, Loyt filter should possess wide tunable ability.
Here, we provide that its tunable range is from 1.0 ?m to 1.7 ?m.
By the reason of size limit of natural calcite, the aperture of Lyot filter is
impossible to be very big, ~36 mm is a reasonable size for manufacturing.
Bandpass FWHM of Lyot filter should match the transmission profile of
Fabry-Perot so as to restrain sidelobes contamination. Simulation for the
interesting near infrared spectral lines is carrying out to determine the last
bandpass FWHM and the thickness of calcite.
In the design of BBSOs IRIM (infrared imaging magnetograph), we used a
4 calcite module in Lyot filter system. The peak transmission is about 37% for the
polarized light. In order to increase the poor transmission, we are considering
to change it into 3-module configuration. The corresponding peak transmission
can reach ~40%.
To keep the tunable ability in 1.0~1.7 ?m, achromatic waveplates and
polarizers are necessary. Some results have been obtained in the design of the
achromatic waveplate and will be given later.
Usually, there are two wavelength tunable method for Lyot birefringent filter:
one is calcite+1/4 waveplate + rotating ˝ waveplate; another is calcite+liquid
crystal variable retarder.
Here, we are considering the first tunable method. As the prefilter of Fabry-Perot, Loyt filter should possess wide tunable ability.
Here, we provide that its tunable range is from 1.0 ?m to 1.7 ?m.
By the reason of size limit of natural calcite, the aperture of Lyot filter is
impossible to be very big, ~36 mm is a reasonable size for manufacturing.
Bandpass FWHM of Lyot filter should match the transmission profile of
Fabry-Perot so as to restrain sidelobes contamination. Simulation for the
interesting near infrared spectral lines is carrying out to determine the last
bandpass FWHM and the thickness of calcite.
In the design of BBSOs IRIM (infrared imaging magnetograph), we used a
4 calcite module in Lyot filter system. The peak transmission is about 37% for the
polarized light. In order to increase the poor transmission, we are considering
to change it into 3-module configuration. The corresponding peak transmission
can reach ~40%.
To keep the tunable ability in 1.0~1.7 ?m, achromatic waveplates and
polarizers are necessary. Some results have been obtained in the design of the
achromatic waveplate and will be given later.
Usually, there are two wavelength tunable method for Lyot birefringent filter:
one is calcite+1/4 waveplate + rotating ˝ waveplate; another is calcite+liquid
crystal variable retarder.
Here, we are considering the first tunable method.
8. Sketch of the NIR Tunable Birefringent Filter This figure is an optical sketch of NIR tunable birefringent filter. Here, P
represents polarizer, C is calcite, ˝ is half waveplate, and ź is quarter waveplate.
The lines beneath the figure indicate the direction of optical axis. This is 4-module
configuration. Each module consists of same structures.
It should be noticed that there are two advantages in the design:
wide-field configuration
For either collimating-mount or telecentric-mount
optical configuration, incident light beam is not normal to surface of birefringent
crystal plates, there will be an error in the retardation of the crystal. In order to
reduce the retardation errors, we adopt wide-configuration: the calcite plate of
an element is split into two equally thick parts and a half waveplate is
sandwiched between them.
wavelength tuning
In every module, there is a rotatable half waveplate. The equation gives the
transmission of the birefringent filter. Rotating these ˝ waveplates can shift the
wavelength of passband within a period in every module.This figure is an optical sketch of NIR tunable birefringent filter. Here, P
represents polarizer, C is calcite, ˝ is half waveplate, and ź is quarter waveplate.
The lines beneath the figure indicate the direction of optical axis. This is 4-module
configuration. Each module consists of same structures.
It should be noticed that there are two advantages in the design:
wide-field configuration
For either collimating-mount or telecentric-mount
optical configuration, incident light beam is not normal to surface of birefringent
crystal plates, there will be an error in the retardation of the crystal. In order to
reduce the retardation errors, we adopt wide-configuration: the calcite plate of
an element is split into two equally thick parts and a half waveplate is
sandwiched between them.
wavelength tuning
In every module, there is a rotatable half waveplate. The equation gives the
transmission of the birefringent filter. Rotating these ˝ waveplates can shift the
wavelength of passband within a period in every module.
9. Instrument II NIR Fabry-Perot Tunable ability: 1.0~1.7 ?m
Clear Aperture: ~ 150 mm
Bandpass FWHM: ~ 0.1 Ĺ @ 15648 Ĺ
Peak Transmission: > 90%
Effective Finesse: ~ 60
FOV: ~ 1 arcmin for spectropolarimeter Prof. Goode, here I just give you a figure to show how to determine the aperture
of Fabry-Perot and FOV.
The following figure is relation between aperture of FP and wavelength shift.
All calculation method is introduced in previous page. So, FOV~1 arcmin and
aperture~150mm should be a good choice.
Prof. Goode, here I just give you a figure to show how to determine the aperture
of Fabry-Perot and FOV.
The following figure is relation between aperture of FP and wavelength shift.
All calculation method is introduced in previous page. So, FOV~1 arcmin and
aperture~150mm should be a good choice.
10. 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
Si CCD
Format: 2048?2048
A/D: 14 bit or 16 bit
Readout: frame transfer
Fill factor: 100%
FOV: 60?
diffraction limit 0.03?@5000Ĺ
sampling 0.029?
QE: >1% In the data acquiring system, we consider to use two set of CCD cameras.
One is visible camera, which is used as images alignment. Another one is near
infrared focal plane array camera. The detailed requirements are shown the
above.
The above is the main design of near infrared tunable filter system. Now, I
would like to spend some time to introduce the process and some results in
the design.In the data acquiring system, we consider to use two set of CCD cameras.
One is visible camera, which is used as images alignment. Another one is near
infrared focal plane array camera. The detailed requirements are shown the
above.
The above is the main design of near infrared tunable filter system. Now, I
would like to spend some time to introduce the process and some results in
the design.
11. Process Design of achromatic waveplates from 1.0 to 1.7?m The above figure gives an example of achromatic quarter waveplate design in
NIR. From 1.0 to 1.7?m, new quarter waveplate shows satisfying retardance.The above figure gives an example of achromatic quarter waveplate design in
NIR. From 1.0 to 1.7?m, new quarter waveplate shows satisfying retardance.
12. Process Measurement of birefringent index of calcite from 1.0 to 1.7?m The birefringent index of a crystal is an important paramenter for the design and
fabrication of a birefringent filter. In the visible light range, the values of the
Birefringent index of calcite and quartz are quite reliable. However, in the IR,
we could extropolate the value up to 1.6?m. Obviously, these known values
of the birefringent index of calcite is unreliable in the NIR. Therefore, the
birefringent index of calcite and its temperature coefficient in the NIR are
measured.The birefringent index of a crystal is an important paramenter for the design and
fabrication of a birefringent filter. In the visible light range, the values of the
Birefringent index of calcite and quartz are quite reliable. However, in the IR,
we could extropolate the value up to 1.6?m. Obviously, these known values
of the birefringent index of calcite is unreliable in the NIR. Therefore, the
birefringent index of calcite and its temperature coefficient in the NIR are
measured.
13. Process 3-module design of Lyot filter to increase transmission In order to improve the poor transmission problem in Lyot filter design, we are
considering to use a 3-module design to replace the old 4-module design.
The above left figure shows the combined transmission of 3-module birefrigent
filter and Fabry-Perot. In order to take a close look of sidelobe contamination,
we present right figure by rescaling the transmission. From the result, the sidelobe
contamination ratio for 3-module system is about 0.54%, compared with 0.40%
for 4-module system. However, the transmission increases from 37% to 45%.In order to improve the poor transmission problem in Lyot filter design, we are
considering to use a 3-module design to replace the old 4-module design.
The above left figure shows the combined transmission of 3-module birefrigent
filter and Fabry-Perot. In order to take a close look of sidelobe contamination,
we present right figure by rescaling the transmission. From the result, the sidelobe
contamination ratio for 3-module system is about 0.54%, compared with 0.40%
for 4-module system. However, the transmission increases from 37% to 45%.
14. 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
In addition, there are several ongoing works. 1.2.3.4
In addition, there are several ongoing works. 1.2.3.4
15. 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
.. The external requirements of near infrared tunable filter system are summarized
as: 1.2.3.4.5
.The external requirements of near infrared tunable filter system are summarized
as: 1.2.3.4.5
.
16. The End Thanks a lot Prof. Goode,
Here is our preliminary design and research progress of the infrared tunable
filter system for ATST. In every page of ppt, I added some footnote which can
help you to understand what we want to express. Obviously, some parameters
are still at the stage of concept design and need time to be determined.
If you have question, please contact with me.
Thank you very much and have a good trip.
WendaProf. Goode,
Here is our preliminary design and research progress of the infrared tunable
filter system for ATST. In every page of ppt, I added some footnote which can
help you to understand what we want to express. Obviously, some parameters
are still at the stage of concept design and need time to be determined.
If you have question, please contact with me.
Thank you very much and have a good trip.
Wenda