iSHELL progress

iSHELL progress
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iSHELL Progress
Current Personnel
• Tokunaga – PI, project management, science case
• Rayner – science case, science requirements, optical
design, thermal design, calibration, alignment plan
• Bond – system requirements, mechanical design,
mechanisms, optical layout, cryostat design, optomechanical
tolerances, alignment plan
• Bonnet – mechanisms, detector mounts (with IRTF
student Alain Khayat)
• Muller – mechanical design, mechanisms, cryostat
design
• Denault, Lockart, Warmbier – array controller,
instrument control (software and electronics)
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Project Developments
iSHELL Progress
• Preliminary Design Review (PDR) for optomechanical,
software, electronics and Critical Design Review (CDR)
for optics set for about August 2012
• iSHELL post-doc position offered to Yuri Belitsky but he
declined. Position is being re-advertised
• IfA student Louis Scudari working with Rayner on
iSHELL simulator
• JPL/Chas Beichman seeking support from NASA
astrophysics for ground-based RV surveys. Proposal
would include funds for iSHELL gas cells and RV
survey
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iSHELL Progress
Remaining optical design tasks to CDR
• Immersion grating specs ✔
• Refractive camera versus TMA/FMA ✔
• Final optical element specs ✔
• Final XD grating specs ✔
• Final order sorting filter specs ✔
• Final ghost image analysis and baffling ✖ (50%)
• Final calibration system design and layout ✖ (50%)
• Optical alignment plan ✖ (50%)
• Optical element mounts ✖
• Negotiate irregularity specs with vendors ✖
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Silicon immersion gratings
• Wavefront RMS 3 x worse than specified
• Need to wait for better gratings (better profile,
and lower scattered light)
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Immersion grating report
D. Jaffe, Univ. of Texas at Austin
01 Feb. 2012

Completed Silicon Immersion Grating for UT’s IGRINS Instrument (July 2011)
/23'456'7089:;

Front-surface interferogram of the IGRINS
grating with a 25mm collimated beam at
633nm. Surface error is 0.17 wave (1/6
wave) peak-to-valley (excellent grating but
note the stripes which represent a 5nm
periodic error).
Diffraction-limited (R=330,000) PSF of the
IGRINS grating at 1.5 microns in immersion (in
red), compared to a mirror PSF).

Efforts for iSHELL Grating. Pursuing:
• Improved contact lithography at UT.
• E-beam lithography in collaboration with JPL.
Grating E06
Contact lithograph prototype
at UT tested in 2011 has 0.3
waves peak-to-valley.
Conclusion is that we need
to improve reactive ion etch
process to keep edges from
folding down. This is well
along.

Interferometry of e-beam patterned parts made at JPL
E09- May 2011. No e-beam stage drift nor current correction
E12- May 2011. E-beam stage drift and current correction every 10 minutes
Color scale is surface error in
waves. These pieces took
about 24 hours of e-beam
time, for a 30x 80 mm pattern
The left figure is the
measurement. The right
shows a model of low-order
Zernike terms.
P-V value of 0.15 waves, or
about half of the contact
lithography wavefront error
from the previous slide

Plans:
• JPL making holders for 30mm thick pieces that are needed for
the iSHELL grating. Plan is to pattern the L and M band grating
on the next attempt.
• We have built holders at UT for reactive ion etching to reduce
edge droop. Will try another contact version of the L and M
grating if there are problems or delays with the JPL e-beam
attempt.
• Patterning/etching step is the key. Once that is completed, the
rest is routine and will take 6-8 months. Goal is to have the
patterned/etched L and M band part by the end of March. J-K
will follow.

iSHELL Progress
Reflective Camera Design from L-3 (SSG)
• Proposed three-mirror solution, good image quality
• Optimum for throughput and scattered light
• Fits in instrument envelope
• Possible issue with 10% image distortion across focal
plane (1% with refractive camera)
• Cost of $500k is too expensive for the project (delivery
of fully tested and aligned system)
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6/21/12 14

iSHELL Progress
Refractive Camera Lens from OSI, Inc.
• BaF 2 – ZnSe – ZnS – LiF
• $60k-$90k, delivery 6-9 months
• BBAR coats $10k-$16k
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iSHELL Progress
Remaining mechanical design tasks to PDR
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iSHELL Progress
Remaining mechanical design tasks to PDR
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iSHELL Progress
Mechanical design next major tasks
• Continued development of the cryostat design –
layout, assembly, access, baffling
• Development of the calibration box can be brought
forward (has been lower priority)
• Mechanism refinements based on the updated
optical bench
• Final thermal and flexure calculations for latest
design including all PDR level subsystems
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iSHELL Progress
Cryostat Structure (concept):
• One optical bench with the fore-optics and
spectrograph on opposite sides
• Optical bench is milled from a single ingot of
aluminum
• Four-point mounting scheme for optical bench
• Nested light-tight shield, actively cooled shield, and
vacuum jacket
• Layout provides good access and ease of assembly
but is traded off against increased volume (iSHELL
0.47 m 3 cf SpeX 0.54 m 3 )
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