hi instrument optical design - astrophysics · – image area = 28 mm x 28 mm ... – faint...

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


• 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


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


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


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


• 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


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


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


• 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


• 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


• 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


• 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


-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


• 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


• 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


• 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


• 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


• 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


Collimator

Optical Fiber

Light Trap

Optical Bench

Detector

Front Baffle Test Mock-Up

Laser Diode

Attenuator

Black Enclosure

HI Optical Testing: Test Mock Up


-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


Light Trap

Detector

Vanes

Collimator

Vanes

Collimated Light

Front Baffle Mockup Tests in Air


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)


Front Baffle Mockup: Air/Vacuum Comparison


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


• 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


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

hi instrument optical design - astrophysics · – image area = 28 mm x 28 mm ... – faint...

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