Freeform optics at ESA: an overview

Transcription

1 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

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 2

3 Challenges in space optical instruments Mass/volume SNR Spectral/spatial resolution Straylight Thermal stability Image quality ESA UNCLASSIFIED - For Official Use Freeform optics at ESA: an overview Charlotte Pachot Freeform workshop 12/10/2017 Slide 3

4 Why use freeform optics in space? Compactness - Decrease mass - Decrease volume Image quality - More degrees of freedom Freeform optics Field of View - Larger - Constant performance Throughput - Less optical elements - Innovative designs ESA UNCLASSIFIED - For Official Use Freeform optics at ESA: an overview Charlotte Pachot Freeform workshop 12/10/2017 Slide 4

5 Freeform optics challenges Surface mathematical definition Optical design optimisation Tolerancing analysis Design Metrology Freeform optics Manufacturing Technique Machine Complexity Time Material Non standard measurement techniques Data file formats Alignment ESA UNCLASSIFIED - For Official Use Freeform optics at ESA: an overview Charlotte Pachot Freeform workshop 12/10/2017 Slide 5

6 Tropomi instrument (1/3) TROPOMI = TROPOspheric Monitoring Instrument Push-broom type imaging spectrometer covering a spectra range from UV to SWIR. Successor of OMI and SCHIAMACHY Launch: 13/10/2017! Instrument main characteristics - UV-VIS-NIR-SWIR nadir view grating spectrometer - Spectral range , , nm - Spatial resolution 7x7 km² at nadir - Swath width 2600 km - Spectral resolution nm (Courtesy:KNMI) ESA UNCLASSIFIED - For Official Use Freeform optics at ESA: an overview Charlotte Pachot Freeform workshop 12/10/2017 Slide 6

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 Tropomi telescope breadboard set-up (courtesy:tno) Drawbacks - Longer manufacturing time Tropomi telescope optical design (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 7

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: Al 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): noncontact 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 ESA UNCLASSIFIED - For Official Use Freeform optics at ESA: an overview Charlotte Pachot Freeform workshop 12/10/2017 Slide 8

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 9

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 57nm SFE after ruling Manufactured freeform grating (Courtesy: AMOS) Microscope view of the grating grooves (Courtesy: AMOS) ESA UNCLASSIFIED - For Official Use Freeform optics at ESA: an overview Charlotte Pachot Freeform workshop 12/10/2017 Slide 10

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 11

12 Application: Elois spectrometer Freeform grating main benefit = Compactness at equal performance Optical performance ELOIS spectrometer Image F# 2.5 Entrance slit 60 mm x 30 µm Image 30 mm (spatial) x 2.7 mm (spectral) Elois spectrometer optical design (Courtesy: AMOS) Grating frequency Spectral range Spectral sampling 104 lp/mm nm 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 Elois spectrometer Breadboard (Courtesy: AMOS) ESA UNCLASSIFIED - For Official Use Freeform optics at ESA: an overview Charlotte Pachot Freeform workshop 12/10/2017 Slide 12

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 13

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 (@ 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 14

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 15

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 16

17 Free-Form Diffraction Gratings and Mirrors Breadboarding Achievements - Activity on-going - Manufacturing starting in Fall Assembly, Integration, Verification in mid 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 17

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 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 18

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 Nominal Optimisation Merit function Optomechanical design Tolerancing MAIT Final ESA UNCLASSIFIED - For Official Use Freeform optics at ESA: an overview Charlotte Pachot Freeform workshop 12/10/2017 Slide 19

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 20

21 Upcoming events ESA UNCLASSIFIED - For Official Use Freeform optics at ESA: an overview Charlotte Pachot Freeform workshop 12/10/2017 Slide 21

22 Upcoming events ESA UNCLASSIFIED - For Official Use Freeform optics at ESA: an overview Charlotte Pachot Freeform workshop 12/10/2017 Slide 22

23 Thank you for your attention! For further information and/or contact: Acknowledgement: SpaceBel, AMOS, TNO, Horiba, CSL ESA UNCLASSIFIED - For Official Use