IGRINS
Immersion GRating INfrared Spectrograph:
Current Design
Sungho Lee
Korea Astronomy and Space Science Institute (KASI) / Univ. of Texas at Austin (UT)
In-Soo Yuk (KASI), Moo-Young Chun (KASI), Soojong Pak (KHU), Hanshin Lee (UT),
Chan Park (KASI), Joseph Strubhar (UT), Weisong Wang (UT), Casey Deen (UT),
Michael Gully-Santiago (UT), Jared Rand (UT), Jung-Hoon Kim (SET), Won-Kee Park
(SNU/KHU), Haingja Seo (KHU), Kang-Min Kim (KASI), Heeyoung Oh (KASI), SangOn Lee (KASI), Marc Rafal (UT), Stuart Barnes (Univ. of Canterbury/UT), John Goertz
(UT), John Lacy (UT), Tae-Soo Pyo (Subaru), Daniel T. Jaffe (UT)
IGRINS Design
SNU 2010-08-26
Instrument Team
Korea
UT
KASI
Project Management
Dan Jaffe (PI),
Marc Rafal
Systems Engineering
Sungho Lee,
Joe Strubhar
Optics
Hanshin Lee
Gratings
Weisong Wang
Mechanics
Cryogenics
In-Soo Yuk (Co-PI),
Chan Park
Electronics
Moo-Young Chun
Software
Calibration Unit
KHU/SET
Soojong Pak,
Jung-Hoon Kim
Kang-Min Kim,
Heeyoung Oh
IGRINS Design
SNU 2010-08-26
IGRINS
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High resolution IR spectrograph which can cover a broad wavelength
range in a single exposure
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IGRINS will be commissioned at the McDonald 2.7-m telescope, and
also designed to be compatible with 4-8 m telescopes.
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Spectral resolution
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Wavelength coverage
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R=40,000 (3.66 pixel sampling)
H-band : 1.49~1.80 µm (25 orders)
K-band : 1.96~2.46 µm (22 orders)
Slit dimension
Telescope
2.7-m
McDonald
4-m
8-m
Slit Width
1”
0.68”
0.34”
Slit Length
15”
10”
5”
IGRINS Design
SNU 2010-08-26
Design Concept
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Cross-dispersed echelle spectrograph
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High sensitivity
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Silicon immersion grating
VPH gratings
HAWAII-2RG (2048x2048) detectors
Compact (0.9 x 0.6 x 0.4 m)
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Main disperser : silicon immersion grating (R3, 36.5 l/mm)
Cross disperser : VPH gratings (H: 650 l/mm, K: 400 l/mm)
Silicon immersion grating
VPH gratings
White pupil optical design
Simple and reliable operation
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No cold moving parts in the spectrograph
Only switching mechanism for the calibration sources
Model of IGRINS on 2.7m
IGRINS Design
SNU 2010-08-26
Optical Design Layout
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Collimated beam size = 25 mm
Slit size = 0.13 mm x 1.94 mm
IGRINS Design
SNU 2010-08-26
H-Band Spectral Format
IGRINS Design
SNU 2010-08-26
K-Band Spectral Format
IGRINS Design
SNU 2010-08-26
Spectrograph Optical Performance
H-band
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Geometric spot diagram across the spectra
Squares: 2 x 2 pixels (36 x 36 micron)
Circles: Airy disk size
Optical quality does not degrade spectral resolution
K-band
IGRINS Design
SNU 2010-08-26
Input Relay Optics
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Convert a telescope f-ratio (f/9-f/16) to f/10
Provide a cold stop to prevent thermal radiation
Deliver 2 x 2 arcmin FOV to the slit-viewing/guiding camera
Circle: Airy disk size
• 1 arcsec seeing disk image through the input optics at the slit mirror
• 4.4 arcsec per size
Left: Center of the slit
Middle: One edge of the slit
Right: One corner of the 2 x 2 arcmin field
IGRINS Design
SNU 2010-08-26
Slit-Viewing Camera
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Target acquisition and slit monitoring
Offset guiding in a 2 x 2 arcmin FOV at the 2.7-m telescope
Use 1024 x 1024 clean area of an Engineering Grade H2RG
Ks-band filter
• 1 arcsec seeing disk image through the input optics
and slit viewer
• 4.4 arcsec per size
Left: Center of the slit
Middle: One edge of the slit
Right: One corner of the 2 arcmin x 2 arcmin field
IGRINS Design
SNU 2010-08-26
Immersion Grating
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Outstanding capability of IGRINS in the compact design comes from the
silicon immersion gratings.
The high refractive index (n=3.4) of silicon keep the high spectral resolution
with a much smaller beam size.
Silicon lithography can make a very coarse grating which enables continuous
spectral coverage.
m  nG (sin   sin  )
Rmax 
2nG L sin 
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d  2nG tan 

d

IGRINS Design
SNU 2010-08-26
IGRINS Immersion Grating
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Silicon R3 grating (10 cm)
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Spectral ghost < 0.3%
(~5 nm periodic error)
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Spectral grass ~10-5
(scattering at groove surfaces)
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Will make another grating
Choose and cut into the shape
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IGRINS Design
SNU 2010-08-26
VPH Gratings
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Volume Phase Holographic grating
Cross-dispersers in each H and K band spectrograph
Advantages of VPH gratings over conventional gratings
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Higher efficiency by less scatters
Enabling compact optical systems by transmission configuration
High durability and easy handling
Has been used in optical and NIR (H-band) spectrographs
We have purchased H-VPHGs which show good performances.
IGRINS Design
SNU 2010-08-26
IR VPH Grating Test
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Performance verification
K-band grating development in collaboration with KOSI
Thermal cycling tests
IGRINS Design
SNU 2010-08-26
Mechanics – Cyrostat
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Size of the cryostat : 900 x 600 x 400 mm
Total mass : 210 kg
Compactness minimizes the flexure issue
All access from the bottom of the cryostat
Optical bench is mounted on the bottom plate and
thermally isolated by G10 supports
Input relay optics
Slit-viewing camera
IGRINS Design
SNU 2010-08-26
Cyrostat – Structual Analysis
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Mostly looking upward to the
straight Cassegrain focus
Deflection is < 10 um at the G10
supports
Corrected out by focussing and
guiding
IGRINS Design
SNU 2010-08-26
Mechanics – Camera Barrels
(H-band, 130 K)
Lens 1
Lens 2
Lens 3
Lens 4
Material
CAF2
S-FTM16
INFRASIL
INFRASIL
Thickness (mm)
5
7.5
11.5
8.5
Diameter (mm)
54
54
54
67
IGRINS Design
SNU 2010-08-26
Mechanics – Camera Barrels
Radial
spring
Axial
spring
3 Baffle
Plates
Radial
spring
Radial Spring
Built in
Baffle
Axial
spring
Axial Spring
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M3 screws
with
helicoil
Bent Holes
Precision
Pin
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Camera is the most sensitive
Design it first to minimize risk
3+1 baffle vanes
3-point kinematic mount
Springs for thermal expansion
IGRINS Design
SNU 2010-08-26
Mechanics – Detector Mounts
Cryo ASIC Board
Flex Cable
Cold Strap
from ASIC
board
H2RG
Cold Strap
from H2RG
Thermal insulation
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Flex cable to the outside electronics
H2RG & ASIC thermally isolated
from the optical bench
IGRINS Design
SNU 2010-08-26
Mechanics – Telescope Mount
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4-point structure
Only translation on the FP
Same mount for 2.7 m and
Gemini
IGRINS Design
SNU 2010-08-26
Cryogenics
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Operating temperature
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2 rubber
springs
Temperature stability control
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Optical bench and optics : 130 K
Detectors : 77 K
Silicon immersion grating : ±0.06 K
Detector : ±0.1 K
Optical bench : ±1 K
The temperature will be monitored at least at six positions
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Cold head, optical bench, radiation shield, input optics, two
spectrograph cameras
Metal
bellows
Vibration isolation design
IGRINS Design
SNU 2010-08-26
Detectors
H & K spectrograph
(Science grade)
ROIC
Detector material
Format (pixels)
Slit-viewing camera
(Engineering grade)
HAWAII-2RG
HgCdTe
2048 x 2048
Pixel size
18 m
Cutoff wavelength
2.5 m
Quantum efficiency
> 80 %
Read noise (CDS)
< 12 e-
Dark current
< 0.01 e-/s/pixel
Controller
SIDECAR ASIC
IGRINS Design
SNU 2010-08-26
Detector Testing
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Collaboration with WIFIS at Univ. of Toronto
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ROIC functional test is ongoing
Cryogenic EG detector test in this year
Test at KASI
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Test dewar design
Cryogenic test at KASI next year
IGRINS Design
SNU 2010-08-26
Electronics Architecture
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IP based control system (each device has an IP address)
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Standard SW protocols and HW devices
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System can evolve as needed.
IGRINS Design
SNU 2010-08-26
Software Architecture
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Standard observing scenarios
Software Requirements Document
Software Specification Document: working for each SW package
IGRINS Design
SNU 2010-08-26
Calibration Unit
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Line Calibration :
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Th-Ar lamp or Uranium lamp
OH emission lines
Telluric absorption lines
Continuum Calibration :
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Tungsten-halogen lamp
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Compatible with f/8 ~ f/16 telescopes
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Considering an absorption gas cell for future RV programs
IGRINS Design
SNU 2010-08-26
Integration and Test
– Lab Setup and Handling Plan
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Clean room, optical bench, interface
Multi-purpose cart
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Storage and transportation
Telescope installation
IGRINS Design
SNU 2010-08-26
Overall Alignment Procedure
Module Alignments (Warm)
[M1] Input-relay
lens module
[M2] Slit-viewer
lens module
[M3] H & K camera
lens module
[M5] Optical
bench assembly
Warm Test
[Sb1] Input-relay optics
[Sb2] Slit-viewer optics
[Sb3] Spectrograph reflective optics
Cold Test
[Sb4] Slit-viewer system
[Sb5] Input+Slitviewer system
[Sb6] Spectrograph system
System Alignments (Cold)
[S1] Instrument alignment
[S2] Telescope alignment
[M4] Calibration
optics
IGRINS Design
SNU 2010-08-26
Fabrication & Alignment Plan
Fabricate and test
H & K camera lenses
Correct design of
H & K camera barrels
Fabricate and test
dispersion part components
Correct design of
M2 mirror mount
Correct positions of
H & K cameras + detectors
Fabricate
H & K camera barrels
Fabricate
dispersion part mounts
Assemble and align
H & K camera barrels
Assemble and align
dispersion part
(compensator: M2 mirror)
Assemble and align
dispersion part + camera barrels + detectors
(compensator: detector assembly)
IGRINS Design
SNU 2010-08-26
Future Work
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Overall timeline
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PDR : 2009. 12
Camera CDR : 2010. 11
Main CDR : 2011 (TBD)
Commissioning : 2012. 11 (TBD)
Tasks for the Camera CDR
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Camera lens barrel design
Scattered light and ghost analysis
Revise engineering requirements: OCDD, FPRD, error
budget
Revise I/T plan, acceptance test plan, alignment plan