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ESA UNCLASSIFIED - For Official Use
Freeform optics at ESA: an overview C.Pachot, A.Zuccaro Marchi, S.Mahalik, M.Miranda, A.Deep, L.Maresi, O.Sqalli, M.Taccola, M.Francois, S.Santandrea European Space Agency ESA, ESTEC, Keplerlaan 1, 2201 AZ Noordwijk ZH, The Netherlands 12-13/10/2017 – Marseille
ESA UNCLASSIFIED - For Official Use Freeform optics at ESA: an overview |Charlotte Pachot | Freeform workshop 12/10/2017 | Slide 2
Outline
Why use freeform optics in space ?
Challenges of Freeform optics
Freeform activities overview
Next steps/Future work
ESA UNCLASSIFIED - For Official Use Freeform optics at ESA: an overview |Charlotte Pachot | Freeform workshop 12/10/2017 | Slide 3
Challenges in space optical instruments
Straylight
Mass/volume Spectral/spatial resolution
Thermal stability
SNR
Image quality
ESA UNCLASSIFIED - For Official Use Freeform optics at ESA: an overview |Charlotte Pachot | Freeform workshop 12/10/2017 | Slide 4
Why use freeform optics in space ?
Freeform optics
Field of View - Larger - Constant performance
Throughput - Less optical elements - Innovative designs
Image quality - More degrees of freedom
Compactness - Decrease mass - Decrease volume
ESA UNCLASSIFIED - For Official Use Freeform optics at ESA: an overview |Charlotte Pachot | Freeform workshop 12/10/2017 | Slide 5
Freeform optics
Design
Manufacturing
Alignment
Metrology
Freeform optics challenges
Surface mathematical definition Optical design optimisation Tolerancing analysis
Technique Machine Complexity Time Material
Non standard measurement techniques Data file formats
ESA UNCLASSIFIED - For Official Use Freeform optics at ESA: an overview |Charlotte Pachot | Freeform workshop 12/10/2017 | Slide 6
TROPOMI = TROPOspheric Monitoring Instrument
Push-broom type imaging spectrometer covering
a spectra range from UV to SWIR.
Successor of OMI and SCHIAMACHY
Instrument main characteristics
- UV-VIS-NIR-SWIR nadir view grating spectrometer
- Spectral range 270-495, 675-775, 2305-2385 nm
- Spatial resolution 7x7 km² at nadir
- Swath width 2600 km
- Spectral resolution 0.25-1.1 nm
Tropomi instrument (1/3)
Launch: 13/10/2017 !
(Courtesy:KNMI)
ESA UNCLASSIFIED - For Official Use Freeform optics at ESA: an overview |Charlotte Pachot | Freeform workshop 12/10/2017 | Slide 7
Tropomi instrument (2/3)
Telescope freeform design
- Heritage from 2-mirror telescope of OMI/SCIAMACHY
- 2 freeform-mirror telescope
Advantages
- Minimize number of optical elements for better performance
- Better spatial resolution (factor 10 to 30)
- Resolution more constant over FoV
Drawbacks
- Longer manufacturing time Tropomi telescope optical design (courtesy:TNO)
Tropomi telescope breadboard set-up (courtesy:TNO)
Paper ICSO: The TROPOMI Telescope Design, Fabrication and Test of a freeform optical system, David Nijkerk, Bart van Venrooy, Peter van Doorn, Rens Henselmans, Folkert Draaisma, André Hoogstrate
ESA UNCLASSIFIED - For Official Use Freeform optics at ESA: an overview |Charlotte Pachot | Freeform workshop 12/10/2017 | Slide 8
Tropomi instrument (3/3) Freeform mirrors design
- Design and analysis using Code V
- 2 toroidal mirrors (size 100mm) -> anamorphic telescope
- Surface shape represented by XY-polynomial
- Tolerance analysis incl. mid-spatial frequencies
- Alignment not necessary post assembly
Freeform mirrors manufacturing
- Prototype of the telescope has been built
- Material: Al6061
- Manufactured by single point diamond turning in slow servo mode (NiP coating to achieve required roughness + manual post polishing) – long process 30 hours
Metrology
- Use of TNO Nanomefos machine (accuracy <15nm rms): non-contact measuring machine with an optical probe
- Volume of the sample up to Diam.500x100 mm
- Best aspherical surface fit deviation up to 5 mm PV
Courtesy: TNO Courtesy: TNO
https://www.tno.nl/en/focus-areas/industry/semiconductor-equipment/industrial-instrumentation/nanomefos-non-contact-measurement-machine-freeform-optics/
ESA UNCLASSIFIED - For Official Use Freeform optics at ESA: an overview |Charlotte Pachot | Freeform workshop 12/10/2017 | Slide 9
ESA-funded R&D activities on freeform optics
TRP/GSTP activities
Feasibility of Diffraction Grating on Free Form Surfaces
Linear variable based hyperspectral instrument - Elois spectrometer
Development of the EQM of a Compact Spectrometer Based on a Free Form Grating
Free-Form Diffraction Grating and Mirrors – Breadboarding
Design Tools & Alignment Concepts for Free-Form Optics
ESA UNCLASSIFIED - For Official Use Freeform optics at ESA: an overview |Charlotte Pachot | Freeform workshop 12/10/2017 | Slide 10
Feasibility of Diffraction Grating on Free Form Surfaces (1/2)
Objectives
• Demonstrate the feasibility of gratings on freeform substrates
• Assess the achievable performance of freeform gratings
• Identify a design concept of hyperspectral imager which can benefit from a freeform
grating
Overview
• TRP contract
• Activity started in 2012, successfully completed in 2015
• Budget 200k€
• Contractor AMOS (BE)
Achievements
• Grating design: 104 lp/mm, on NiP Aluminium 6061T6 alloy
• Freeform substrate machined by single point diamond turning
• Grating grooves engraved directly on the surface by diamond tool
Microscope view of the grating grooves (Courtesy: AMOS)
Manufactured freeform grating (Courtesy: AMOS)
57nm SFE after ruling
ESA UNCLASSIFIED - For Official Use Freeform optics at ESA: an overview |Charlotte Pachot | Freeform workshop 12/10/2017 | Slide 11
Feasibility of Diffraction Grating on Free Form Surfaces (2/2)
Hyperspectral imager concept
- Starting point
- Sentinel 5p Tropomi instrument requirement specification
- Offner spectrometer with 1:1 magnification
- Concept
- 2:1 magnification Offner spectrometer using a freeform
grating on a convex mirror surface
- Achievements
- Increase of the SNR
- Minimisation of the volume
- Good image quality over FoV
ESA UNCLASSIFIED - For Official Use Freeform optics at ESA: an overview |Charlotte Pachot | Freeform workshop 12/10/2017 | Slide 12
Application: Elois spectrometer
Freeform grating main benefit =
Compactness at equal performance
Elois spectrometer optical design (Courtesy: AMOS)
Elois spectrometer Breadboard (Courtesy: AMOS)
Optical performance
ELOIS spectrometer
Image F# 2.5
Entrance slit 60 mm x 30 µm
Image 30 mm (spatial) x 2.7 mm (spectral)
Grating frequency 104 lp/mm
Spectral range 450-900 nm
Spectral sampling 2.5 nm
Keystone 1.1 µm
Smile 1.9 µm
Global size 116 x 145 x 130 mm (with folding)
Elois spectrometer Breadboard (Courtesy: AMOS)
C. DeClercq, V. Moreau, J.-F. Jamoye, A. Zuccaro Marchi, P. Gloesener 2015, “ELOIS: an innovative spectrometer design using a free-form grating”, Proc. SPIE 9626
ESA UNCLASSIFIED - For Official Use Freeform optics at ESA: an overview |Charlotte Pachot | Freeform workshop 12/10/2017 | Slide 13
Development of the EQM of a Compact Spectrometer Based on a Free Form Grating Motivation
Freeform grating Offner topology provides a very compact and lightweight solution for implementation of a high performing spectrometer
Develop a full instrument capitalizing on the ELOIS spectrometer breadboarding experience
Objectives
• Extend and demonstrate the freeform grating offner spectrometer concept to the VNIR and SWIR wavelengths within one compact instrument covering the following spectral range: 400 nm to 2450 nm.
• Design, manufacturing, testing of an EQM of the complete payload
Overview
GSTP activity
Started in December 2016, 2.5 years activity
Contractor SpaceBel, AMOS (+Caeleste, CSL, DeltaTec)
ESA UNCLASSIFIED - For Official Use Freeform optics at ESA: an overview |Charlotte Pachot | Freeform workshop 12/10/2017 | Slide 14
Development of the EQM of a Compact Spectrometer Based on a Free Form Grating Main characteristics
- Overall payload designed to be compatible with Proba-Next platform (mass, volume, on-board resources)
- Design envelope Sun Synchronous orbit:
- LTDN/LTAN: 10:00 AM – 12:00 AM
- Altitude: 590km - 670km
- Swath width: 70 km (@ Nadir) @642 km altitude
- Capability to image with an +/- 30 deg across track off-pointing
- Optical telescope (front-end optics) single TMA
- Beam-Splitter to separate VNIR and SWIR channels (@ 900 nm)
ESA UNCLASSIFIED - For Official Use Freeform optics at ESA: an overview |Charlotte Pachot | Freeform workshop 12/10/2017 | Slide 15
Free-Form Diffraction Gratings and Mirrors – Breadboarding
Motivation
• Encouraging results from TRP on freeform grating
• Objective to increase the groove density of the grating
Objectives
• Design, alignment, manufacturing and testing of a freeform grating spectrometer according ESA requirements
• Freeform grating > 1000gr/mm manufacturing and testing
Overview
• TRP activity
• Activity started in Sept 2016
• Budget 500 k€
• Contractor AMOS/HORIBA/CSL
ESA UNCLASSIFIED - For Official Use Freeform optics at ESA: an overview |Charlotte Pachot | Freeform workshop 12/10/2017 | Slide 16
Free-Form Diffraction Gratings and Mirrors – Breadboarding
Optical design - High spectral resolution and SNR - Compactness Freeform design Freeform grating Freeform Blazed Holographic grating of 1000 gr/mm (± 2 mm deviation to BFS) Sketch of the Optical design (Courtesy: AMOS)
Payload opto-mechanical design (Courtesy: AMOS)
ESA UNCLASSIFIED - For Official Use Freeform optics at ESA: an overview |Charlotte Pachot | Freeform workshop 12/10/2017 | Slide 17
Free-Form Diffraction Gratings and Mirrors – Breadboarding
Achievements
- Activity on-going
- Manufacturing starting in Fall 2017
- Assembly, Integration, Verification in mid 2018
- Full Focal plane characterization through Summer 2018 (CSL)
ESA UNCLASSIFIED - For Official Use Freeform optics at ESA: an overview |Charlotte Pachot | Freeform workshop 12/10/2017 | Slide 18
Design Tools & Alignment Concepts for Free-Form Optics
Motivation
Existing ray-tracing software optimisation algorithms (Code V, Zemax) are not optimised for freeform surfaces
• Not converging in the optimisation process
• Optimisation phase of optical designs involving freeform slow
Objectives
• Define the baseline mathematical description of free-form surfaces;
• Define procedure and best practices for optical design using free-form components;
• Demonstrate advantage of the developed free-form design tools on two case studies;
• Develop alignment strategy and test methods with accuracy compatible with the two case studies.
Overview
• TRP activity
• Activity started in Sept 2016, Final Review planned Dec. 2017
• Budget 350 k€
• Contractor TNO (NL)
Zernike polynomials
ESA UNCLASSIFIED - For Official Use Freeform optics at ESA: an overview |Charlotte Pachot | Freeform workshop 12/10/2017 | Slide 19
Design Tools & Alignment Concepts for Free-Form Optics
Achievements
- Activity on-going
- Optimisation tool developed in Python, delivery as a plug-in to existing optical software Code V
- Work with any definition of freeform surfaces: Q-polynomials, NURBS, Zernike… but optimisation tool will be tested on 2 mathematical descriptions (from in-built capabilities of Code V) in the frame of this activity
•Requirements •Mathematical description
Concept
• Optimisation • Merit function
Nominal •Opto-mechanical design
• Tolerancing • MAIT
Final
ESA UNCLASSIFIED - For Official Use Freeform optics at ESA: an overview |Charlotte Pachot | Freeform workshop 12/10/2017 | Slide 20
Next steps/future work
• Analytical part
• Straylight from freeform surfaces
• Large scale manufacturing and metrology tools
• Alignment
ESA UNCLASSIFIED - For Official Use Freeform optics at ESA: an overview |Charlotte Pachot | Freeform workshop 12/10/2017 | Slide 21
Upcoming events
https://atpi.eventsair.com/QuickEventWebsitePortal/space-engineering-and-technology-final-presentations-days/set-pfds
ESA UNCLASSIFIED - For Official Use Freeform optics at ESA: an overview |Charlotte Pachot | Freeform workshop 12/10/2017 | Slide 22
Upcoming events
https://atpi.eventsair.com/QuickEventWebsitePortal/workshop-on-innovative-technologies-for-space-optics/workshop-on-innovative-technologies-for-space-optics
ESA UNCLASSIFIED - For Official Use
Thank you for your attention !
Acknowledgement: SpaceBel, AMOS, TNO, Horiba, CSL
For further information and/or contact: [email protected]