optical design & analysis paul martini · optical design & analysis paul martini july 6th,...
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![Page 1: Optical Design & Analysis Paul Martini · Optical Design & Analysis Paul Martini July 6th, 2004. Harvard-Smithsonian Center for Astrophysics MMIRS PDR PM 2 Outline • Optical Design](https://reader030.vdocuments.net/reader030/viewer/2022041010/5eb8a73fd0b2f01a0a726376/html5/thumbnails/1.jpg)
Harvard-SmithsonianCenter for Astrophysics
MMIRS PDR PM 1
Optical Design & AnalysisPaul Martini
July 6th, 2004
![Page 2: Optical Design & Analysis Paul Martini · Optical Design & Analysis Paul Martini July 6th, 2004. Harvard-Smithsonian Center for Astrophysics MMIRS PDR PM 2 Outline • Optical Design](https://reader030.vdocuments.net/reader030/viewer/2022041010/5eb8a73fd0b2f01a0a726376/html5/thumbnails/2.jpg)
Harvard-SmithsonianCenter for Astrophysics
MMIRS PDR PM 2
Outline
• Optical Design• Filters and Grisms• Pupils• Throughput Estimate• Ghost Analysis• Tolerance Analysis• Critical Areas• Task List
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Harvard-SmithsonianCenter for Astrophysics
MMIRS PDR PM 3
Requirements
• Multislit spectroscopy over a wide field low to moderate resolution
• Wide field imaging• Slit mask exchange during daylight• Illuminate a 2048x2048 HAWAII-2 array
with adequate sampling
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Harvard-SmithsonianCenter for Astrophysics
MMIRS PDR PM 4
Heritage
• Two-dewar design from R. Elston• Original MMIRS design by H. Epps• Modifications by D. Fabricant
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Harvard-SmithsonianCenter for Astrophysics
MMIRS PDR PM 5
Overview
• Fully illuminated 7’x7’ field of view• Multislit spectroscopy over 4’x7’
– Some loss of spectral coverage outside 2’x7’• J+H or H+K spectroscopy at R=1500• J, H, or K spectroscopy at R=3000• Y, J, H, K, J+H, and H+K filters
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Harvard-SmithsonianCenter for Astrophysics
MMIRS PDR PM 6
Optical Layout
Corrector
Slit Plane
Collimator
Camera
Detector
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Harvard-SmithsonianCenter for Astrophysics
MMIRS PDR PM 7
Corrector DetailCaF2
D=14’139.4mm
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Harvard-SmithsonianCenter for Astrophysics
MMIRS PDR PM 8
Full Corrected FieldGuide camera field Science Field
D = 14 arcmin 7x7 arcmin
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Harvard-SmithsonianCenter for Astrophysics
MMIRS PDR PM 9
Corrector PerformanceSlit Plane
Guider
1 pixelbox
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Harvard-SmithsonianCenter for Astrophysics
MMIRS PDR PM 10
Collimator/Camera Detail
CaF2
FQTZ
BaF2
ZnSe
S-FTM16
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Harvard-SmithsonianCenter for Astrophysics
MMIRS PDR PM 11
Collimator/Camera RMS Spots
2 pixelbox
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Harvard-SmithsonianCenter for Astrophysics
MMIRS PDR PM 12
Collimator/Camera Spots & EEJ H K
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Harvard-SmithsonianCenter for Astrophysics
MMIRS PDR PM 13
Filters
• 2 filter wheels with 6 positions each• Y, J, H, K filters• J+H and H+K filters for spectroscopy• Large filters: 120mm diameter• Identified a consortium to reduce cost• Space for several future filters
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Harvard-SmithsonianCenter for Astrophysics
MMIRS PDR PM 14
Grisms
• Five Grisms on CaF2
15000.08021H+K
15000.09418J+H
30000.1341K
30000.17541H
30000.2341J
RGrooves/µmAngleBand Flamingos-2
18 0.098
21 0.082
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Harvard-SmithsonianCenter for Astrophysics
MMIRS PDR PM 15
Pupils
• Two pupils as compromise between throughput and thermal blocking
• Fixed, oversized pupil used by all observing modes
• Undersized pupils directly attached to K and H+K filters (one for each) to minimize thermal contamination
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Harvard-SmithsonianCenter for Astrophysics
MMIRS PDR PM 16
Throughput Estimate
• Imaging estimate: 40%• Spectroscopy estimate: 30%• Assumptions:
– Surface losses: 2% per surface (28 surfaces in imaging mode) or 56%
– Filter losses: 10% (2 more surfaces)– Pupil losses: 0-5%– Grism losses: 25% (3 more surfaces)– Detector QE 75%
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Harvard-SmithsonianCenter for Astrophysics
MMIRS PDR PM 17
Ghost Analysis
• Lenses assumed to be 1% reflective, detector 40%
• Ghosts minimized in optical design stage• Imaging mode
– Reflection off filters avoided by tilting filters• Spectroscopy mode
– Reduced transmission, although addition of surface at a conjugate point
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Harvard-SmithsonianCenter for Astrophysics
MMIRS PDR PM 18
Ghost Results
• Reflectance of (back of) slit masks should be minimized
• No ghost images identified• Strongest ghost pupils are either very
vignetted or uniformly fill the field
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Harvard-SmithsonianCenter for Astrophysics
MMIRS PDR PM 19
Tolerance
• Present design produces rms spot radius of 10 microns on the detector and 4 microns at the slit plane
• Goal: <14 micron spot radius at the detector and <10 micron spot radius at the slit plane
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Harvard-SmithsonianCenter for Astrophysics
MMIRS PDR PM 20
Error Budget
• Lens constraints:– surface radii and quality– surface decenter and tilt– element thickness
• Element constraints:– element decenter and tilt– spacing between elements– group decenter and tilt
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Harvard-SmithsonianCenter for Astrophysics
MMIRS PDR PM 21
Input Lens Constraints
• Radii: 0.1%• Flats: 2 fringes• Surface Irregularities: 0.5 fringes• Thickness 0.05mm• Surface tilt: 0.01mrad• Surface decenter: 0.01mm
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Harvard-SmithsonianCenter for Astrophysics
MMIRS PDR PM 22
Input Element/Group Constraints
• Spacing: 0.1mm• Element tilt: 0.1mrad• Element decenter: 0.05mm• Group tilt: 0.2mrad• Group decenter: 0.1mm
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Harvard-SmithsonianCenter for Astrophysics
MMIRS PDR PM 23
Analysis Method
• Inverse Sensitivity analysis in ZEMAX to compute first pass tolerance budget
• Identify critical constraints and rebalance the tolerance budget
• Set goal of <14 micron spot radius• Run Monte Carlo realizations • Determine mechanical constraints that
achieve goal with 90% probability
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Harvard-SmithsonianCenter for Astrophysics
MMIRS PDR PM 24
Tolerance Simulations
4 5 6 78 9 10
11 12 13 - 20 21 22 - 27 28-34
L1 L2 L3 L4 L5 - L8 L9 - L11 L12 - L14
Lenses and Surfaces
Lens Groups
G1 G2 G3 G4
G5 G6
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Harvard-SmithsonianCenter for Astrophysics
MMIRS PDR PM 25
Potential degradation
As designed “Worst case”
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Harvard-SmithsonianCenter for Astrophysics
MMIRS PDR PM 26
Mechanical Requirements
• Lens spacings: several require 0.05mm• Lens tilts: many require 0.1mrad; one 0.05
mrad (although most closely packed)• Lens decenter: several require 0.025mm• Group tilt: several require 0.1mrad• Group decenter: several require 0.05mm;
one 0.025mm
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Harvard-SmithsonianCenter for Astrophysics
MMIRS PDR PM 27
Critical Areas
• Lens spacing: L4-L5, L9-L10, L13-L14• Lens tilt: L3, L4, L10-L13• Lens decenter: L4, L5• Group tilt: G2, G3, G4, G6• Group decenter: G2
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Harvard-SmithsonianCenter for Astrophysics
MMIRS PDR PM 28
Task List
• Identify vendors for optics and coatings• Finalize design with melt sheet data• Test plate fitting to reduce costs• Thermal gradient sensitivity study• Mechanical deflection sensitivity study• Finalize selection of Grisms• Obtain filters• Stray light analysis (in progress)
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Harvard-SmithsonianCenter for Astrophysics
MMIRS PDR PM 29
Summary
• “Penultimate” optical design in hand• Lens sizes and materials are available
from multiple vendors• Filters and Grisms are attainable• Ghost images and pupils are negligible• Tolerance analysis has identified critical
areas for consideration in mechanical design