HI Instrument Optical Design
J.M. Defise, J.Ph. Halain, E. Mazy, P.Rochus
Centre Spatial de Liège – Belgium
021104-06SECCHI_CDR_HI Optical.1
Optical Requirements
021104-06SECCHI_CDR_HI Optical.2
• HI-1
– FOV: 20° From 13.7 to 88.7 Rs
– Image Area = 28 mm x 28 mm (13.5 µm pixels)
– Spectral Range: 630 - 730 nm
– Aperture: 16 mm
– Max Background Noise: 5 10-13
• HI-2
– FOV: 70° From 68.9 to 331.4 Rs
– Image Area = 28 mm x 28 mm (13.5 µm pixels)
– Spectral Range: 400 - 900 nm
– Aperture: 7 mm
– Max Background Noise: 10-14
Optics Design
021104-06SECCHI_CDR_HI Optical.3
Solar light
Forward BaffleInternal Baffle
HI 1HI 2
• Main Challenges:
– Faint Detection Capability ⇒ High Stray-Light Rejection Requirements (Ghosts)
– Large FOV ⇒ Specific Optics HI-1 and HI-2
– Large Spectral Range for HI-2
Optics Design: HI-1
021104-06SECCHI_CDR_HI Optical.4
f = 78 mmAperture 16 mm
FOV 20°
LAK9
LAK9
BK7
LF5
88 mm
• Design Drivers:
– Minimize Size of Lens #1 (Entrance Pupil on Lens #1)
– 20° FOV
– Radiation Tolerant Glasses
– Ghost Rejections
– Margins on MechanicalMount
• Design Performance:
– Minimized RMS Spot Diameter
– Designed for Extended Thermal Range [-20°C , +30°C]
Optics Design: HI-1
021104-06SECCHI_CDR_HI Optical.5
4 3 2 1 0 1 2 3 41 .10 19
1 .10 18
1 .10 17
1 .10 16
1 .10 15
1 .10 14
1 .10 13
1 .10 12
1 .10 11
1 .10 10
1 .10 9
1 .10 8
1 .10 7
GhostBubble (B1)Micro-roughness (2 nm)
[mm]
B/B
0
• RMS Spot Diameter:
– Φ < 20.7 µm
• Ghost Images:
– Φ > 3.5 mm
• Coatings:
– SiO2 on Surface #1
– High Pass Coating > 630 nm
– Low Pass Coating < 730 nm
– AR Coatings on Other Surfaces
Optics Design: HI-2
021104-06SECCHI_CDR_HI Optical.6
• Design Drivers:
– Ghost Images
– Large Spectral Range (400-900 nm)
– 70° FOV
– Radiation Tolerant Glasses
• Design Performance:
– Minimized RMS Spot Diameter
– Maximized Ghost Diameters
– Designed for Extended Thermal Range [-20°C , +30°C]
– Minimized Incidence Angle on Optical Surfaces for Coating Efficiency
SF6
SF6SF4 BK7
SK16SF6
46 mm
f = 20 mmAperture 7 mmFOV 70°
HI-2
Optics Design: HI-2
021104-06SECCHI_CDR_HI Optical.7
15 10 5 0 5 10 151 .10 20
1 .10 19
1 .10 18
1 .10 17
1 .10 16
1 .10 15
1 .10 14
1 .10 13
1 .10 12
1 .10 11
1 .10 10
1 .10 9
1 .10 8
Ghost (mv = -5) µroughness (1 nm)Bubble (B1)
[mm]
B/B
0
• RMS Spot Diameter:
– Φ < 47.2 µm
• Ghost Images:
– Φ > 3 mm
• Coatings
– SiO2 On Surface #1
– AR Coatings on Other Surfaces (MgF2)
– No Bandpass Filter
Optics Design: Budgets
021104-06SECCHI_CDR_HI Optical.8
HI-2
• Error Budget Including:
– Lens Figuring
– Lens Positioning
– Glass Properties Uncertainties
– Thermal Changes With Titanium Lens Mounts Within [-20°C,+30°C]
– Detector Positioning
– ⇒ RMS Spot Diam. Between 105 µm and 145 µm
HI-1
• Error Budget Including:
– Lens Figuring
– Lens Positioning
– Glass Properties Uncertainties
– Thermal Changes With Titanium Lens Mounts Within [-20°C,+30°C]
– Detector Positioning
– ⇒ RMS Spot Diam. Between 45 µm and 69 µm
Changes Since PDR
021104-06SECCHI_CDR_HI Optical.9
• HI-1 Spectral Range Slightly Shifted From 650-750 to 630-730 nm (to Allow Interferometric Tests at 633 nm)
• HI-2 Effective Focal Length Adjusted to Cope With Distortion Effects
• Glass Selection With Supplier Availability (HI-1 & HI-2)
• Tolerance Budget Updated With Lens Barrel Design and Thermal Behavior
HI Baffle Design
021104-06SECCHI_CDR_HI Optical.10
• Stray-Light Rejection Requirements:
– HI-1: Instrumental Background <5 10-13 B0
– HI-2: Instrumental Background<10-14 B0
• Major Stray-Light Contributors and Dedicated Baffles:
– Direct Solar Light (B0): Front Baffle
– Bright Sources in and Out FOV (Planets, Stars): Inner Baffle
– Payload Elements Near UFOV: Perimeter Baffle
HI Baffle Design: Front Baffle
021104-06SECCHI_CDR_HI Optical.11
• HI Front Baffle Is Key Element in Background Light Reduction
• It Has to Provide a 10-9 Rejection Factor for HI-1 (Assuming 10-4 Internal Rejection) [a Single Vane System Would Only Provide a 10-4 Rejection]
1.E-121.E-111.E-101.E-091.E-081.E-071.E-061.E-051.E-041.E-031.E-021.E-011.E+00
0 0.02 0.04 0.06 0.08 0.1
X [mm]
Rej
ectio
n le
vel
vane #1
vane #2
vane #3
vane #4
vane #5
HI-1 optics HI-2 optics
forward baffleHI-1
HI-2X
Cascade Fresnel Edge-Diffraction System
HI Baffle Design: Inner Baffle
021104-06SECCHI_CDR_HI Optical.12
• HI Inner Baffle Is Based on Multi-Reflections on Absorbing Surfaces
• It Has to Protect HI-1 and HI-2 From Planets and Bright Stars Light Reflection on HI Structure
• Ray Trace Analyses Were Used to Define and Optimize Baffle Geometry, Taking Into Account Manufacturing Constrains
HI Optical Analysis
021104-06SECCHI_CDR_HI Optical.13
-80 -70 -60 -50 -40 -30 -20 -10 0 10 20 30 40 50 60 70 8080
70
60
50
40
30
20
10
0
-10
-20
-30
-40
-50
-60
-70
-80
xy angle
zx a
ngl
e
SWAVES Boom
HI-2 CCD
Earth
HI-1 FOV
HI-2 FOVHI-1CCD
Zodiacal light and stars
Planet 1 Planet 3
Planet 2Sun• Contributors to
Instrument Background:
+ xy°
- xy°
0°
+ zx°- zx°
0°
y
zx
HI Optical Analysis
021104-06SECCHI_CDR_HI Optical.14
• Overall Stray-Light Background in HI-1
1.E-21
1.E-20
1.E-19
1.E-18
1.E-17
1.E-16
1.E-15
1.E-14
1.E-13
1.E-12
Earth Stars Zodiacal Swaves Planets Sun Total
maximum HI-1 acceptable background level
Total HI-1 stray-light at FPA level (B/B0)
806040200-20-40-60-80
80
40
0
-40
-80
1.E-141.E-131.E-121.E-111.E-101.E-091.E-081.E-07
[B/B0]
[deg]
[deg]
HI-1 stray-light sky map
HI Optical Analysis
021104-06SECCHI_CDR_HI Optical.15
• Overall Stray-Light Background in HI-2
Total HI-2 stray-light at FPA level (B/B0)
1.E-21
1.E-20
1.E-19
1.E-18
1.E-17
1.E-16
1.E-15
1.E-14
1.E-13
1.E-12
Stars Swaves Sun Earth Zodiacal Planets Total
maximum HI-2 acceptable background level
806040200-20-40-60-80
80
40
0
-40
-80
1.E-141.E-131.E-121.E-111.E-101.E-091.E-081.E-07
[B/B0]
[deg]
[deg]
HI-2 stray-light sky map
HI Optical Analysis – Conclusions
021104-06SECCHI_CDR_HI Optical.16
• Front Baffle Has Been Designed to Provide Required Rejection of Sun Light (Better Than 10-9 for HI-1 and 10-11 for HI-2)
• Internal Baffle Has Been Designed to Provide a 2.10-14 and 9. 10-15
Rejection Level for HI-1 and for All Other Stray-Light Sources
• Optics Have Been Optimized to Avoid Ghost Problems
• Raytrace Studies Have Shown an Additional Margin Due to Lens Barrel and Focal Plane Out-of-Field Attenuation (10-6 Rejection)
• Overall Theoretical Straylight Background Meets Science Requirement
HI Optical Testing
021104-06SECCHI_CDR_HI Optical.17
• HI Success Directly Relies on Rejection Performance of Front Baffle (< 10-9 at HI-1 Level)
– Design Is Based on Theoretical Analyses (Fresnel Diffraction)
– Preliminary Verifications Indicated Rejection Better Than 10-6
• Inner Baffle Performance Is Directly Related to Absorbing Properties of Black Coatings Used on CFRP Vanes
• Verification Program Has Been Set up to Demonstrate Experimentally Front Baffle Performance and Black Coating Scattering Properties in Facilities of Centre Spatial De Liège (B)
Optical Testing: Test Set-Up
021104-06SECCHI_CDR_HI Optical.18
• Goal: Measure Diffracted Light by Cascade Knife Edge System at Level of HI-1 and HI-2 (10-9 and 10-11 Rejection Factors)
– Front Baffle Mock-Up
– Powerful Collimated Beam: 20 W Continuous Laser Diode + Optical Fiber + Collimator
– High Sensitivity Detector: Photomultiplier Used in Photon Counting Mode
– Protection Against External Light and Internal Reflection: Set-Up Is Installed in a Black Enclosure
– “Super Light Trap” to Absorb All Unshaded Direct Flux (108 Efficiency)
– Possibility to Run Test Under Vacuum to Avoid Air Perturbations: Test Set Up Is Implemented in a Vacuum Chamber
HI Optical Testing: Test Set-Up
021104-06SECCHI_CDR_HI Optical.19
Collimator
Optical Fiber
Light Trap
Optical Bench
Detector
Front Baffle Test Mock-Up
Laser Diode
Attenuator
Black Enclosure
HI Optical Testing: Test Mock Up
021104-06SECCHI_CDR_HI Optical.20
-12
-10
-8
-6
-4
-2
0-0
.1 0.1
0.3
0.5
0.7
0.9
1.1
1.3
1.5
1.7
1.9
2.1
2.3
2.5
2.7
2.9
3.1
3.3
3.5
3.7
3.9
Rotation around last vane edge [arcdeg]
Log
(I /
I0)
DiffractedIntensity
Detector
Predicted Shadow
Distribution:
HI Optical Testing: Test Set-Up
021104-06SECCHI_CDR_HI Optical.21
Light Trap
Detector
Vanes
Collimator
Vanes
Collimated Light
Front Baffle Mockup Tests in Air
021104-06SECCHI_CDR_HI Optical.22
1.E-12
1.E-10
1.E-08
1.E-06
1.E-04
1.E-02
1.E+00
1.E+02
-7-6-5-4-3-2-101
Angular offset [arcdeg]
Inte
nsity
Pro
file
[B/B
0]
Theoretical values
1 vane (measured)
5 vanes (measured)
4 vanes (measured)3 vanes (measured)
2 vanes (measured)
021104-06SECCHI_CDR_HI Optical.23
Front Baffle Mockup: Air/Vacuum Comparison
021104-06SECCHI_CDR_HI Optical.24
Front Baffle QM: Preliminary Measurements
• ⇒ Good Indications That the Front Baffle Will Meet the Specification for Rejection Requirements
• Test to Be Pursued With Alignment and Dimensional Checks
STEREO - SECCHI- HI Front Baffle : Diffraction Measurements on EQM
1.E-12
1.E-11
1.E-10
1.E-09
1.E-08
1.E-07
1.E-06
1.E-05
1.E-04
1.E-03
1.E-02
1.E-01
1.E+00
1.E+01
-4-3.5-3-2.5-2-1.5-1-0.500.5Angular offset [arcdeg]
Rel
ativ
e In
tens
ity P
rofil
e [B
/B0]
EQM (air)
Theory
HI-1 front lens location
(air)
Front Baffle Tests - Conclusions
021104-06SECCHI_CDR_HI Optical.25
• Concept of Front Baffle Has Been Demonstrated by Analyses and Tests
• New Test Set-Up Has Been Developed and We Have Measured Unprecedented Experimental Data With Rejection Levels Down to 10-11
• Measurements Are Consistent With Theoretical Data (Mock-Up Tests) Therefore We Can Rely on Our Theoretical Data for:
– Design Optimization– Misalignment Sensitivity Evaluations
• Tests on HI Hardware Still Need to Be Pursued, and Are Going on at CSL
021104-06SECCHI_CDR_HI Optical.26
Inner Baffle Verification: BRDF Measurements
Laser source
Detector
Sample
|α inc|
-
+
α obs
D
S
• BRDF = Major Input for RaytraceAnalysis of Inner Baffle
• Z307 Data Not Yet Published• Raytrace Analyses Conducted With
Z306 Data• Measurements Shows Similar BRDF,
Which Confirms Our Previous Analyses
0.001
0.01
0.1
1
-80 -60 -40 -20 0 20 40 60 80[deg]
0 deg15 deg30 deg45 deg60 deg
Z307 Paint
0.001
0.01
0.1
1
-80 -60 -40 -20 0 20 40 60 80[deg]
0 deg15 deg30 deg45 deg60 deg
Z306 Paint