The TROPOMI Telescope

Transcription

1 The TROPOMI Telescope Design, fabrication and test of a freeform optical system Authors: David Nijkerk Bart van Venrooy Peter van Doorn Rens Henselmans Folkert Draaisma André Hoogstrate Presented by Ad Verlaan

2 Contents TNO and optics General Optics manufacturing Freeform optics TROPOMI Evolution of requirements Optical design Telescope manufacturing Diamond turning NANOMEFOS Testing Breadboard

3 OPTO-MECHANICAL INSTRUMENTATION TNO & Optics Space instruments Earth observation spectrometers Calibration Attitude sensors Space Science Leading customers: ESA, NASA, EADS. Astronomy Delay lines Star separators Adaptive optics Leading customers: ESO, UK-ATC. Semicon System design Sensors Contamination control Substrate handling Semicon equipment Leading customers: ASML, Philips. Other application areas Fiber Bragg gratings Fusion diagnostics Medical applications NANOMEFOS Leading customers: EFDA, NS, Defence.

4 Main goal: TNO & optics: optical workshop Production of special optics used in opto-mechanical designs developed by TNO

5 Design Pre-machining (milling/grinding) Measuring TNO Freeform program Iterative loop Local (corr.) polishing SPDT with onmachine metrology NANOMEFOS absolute metrology Iterative loop Coating Assembly & Alignment

6 TROPOMI: TROPOspheric Monitoring Instrument Push broom telescope scheduled for launch 215 Successor to OMI (Ozone Monitoring Instrument, launched 24) Required improvements Larger wavelength range (UV, NIR, and SWIR) More products: CO and CH 4 Higher accuracy Higher resolution: 7 x 7 km 2 Details of pollution Cloud free imaging Larger field of view (18Deg.) f/9 by f/1 26 km 7 km

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8 Resolution to solve cloud issue If any cloud is present within a pixel, data is useless SCIAMACHY (12 x 3 km 2 ) cloud free (blue) TROPOMI (7 x 7 km 2 ) cloud free (blue)

9 Design of the OMI telescope Primary mirror OMI telescope: spherical mirrors 3 km resolution (13x24 after binning) Polarization scrambler Secondary mirror Spectrometer entrance slit Entrance pupil Field limiting apertures

10 From OMI to TROPOMI Telescope resolution budget: <1 km (.5 in entrance pupil) Anamorphic: different power in flight and swath Aberration correction using freeforms: non-overlapping field points at M1; suitable to compensate field-dependent aberrations. But how? Investigate aberrations using ray aberration curves M1 close to intermediate field to earth spectrometer slit

11 Ray aberration curves Aberration plotted vs position in aperture Atypical field dependent astigmatism introduced by the secondary mirror Corrected by including toroidicity in primary mirror that varies with the field location Edge FOV ( X, Y ) Y-FAN 1.,..5 RELATIVE FIELD (.2, O -.8) O 5.75,. RELATIVE FIELD (-.4, O -.4) O 4.5,. RELATIVE FIELD (-.5, O -.2) O 3.25,. RELATIVE FIELD (-.3, O -.) O 2 X-FAN ,. RELATIVE FIELD (., O.) O.5 TROPOMI Centre FOV -.5 RAY ABERRATIONS ( MILLIMETERS ) MDN 19-Jul NM

12 Nominal performance Resolution gain by including non-symmetric local toroidicity: factor of 2 in comparison with OMI Mirror 1 (xy-terms) y-axis x-axis 5

13 Tolerancing of freeform Non-conventional optics: imperative to address midspatials User defined tolerancing using cosine-shaped ripple of varying amplitude and spatial frequency TION TION TION DG DG DG 6 DG 6 DG 6 DG 1 DG 1 DG 1 DG 3 DG 3 DG 3 DG 6 DG 6 DG 6 DG 823. MM.1E+4 MM.1E+4 MM USING. TROPOMI UVN/SWIR telescope USING. TROPOMI UVN/SWIR telescope USING. TROPOMI UVN/SWIR telescope

14 Diamond turning Freeform has ~ 1 mm deviation from rotationally symmetric shape Single Point Diamond Turning (Precitech 7A) Aluminium body Aluminium cannot meet roughness requirement Solution: Pre-turn Aluminimum Finish turn Nickel Phosphorous plating Hand polishing step to roughness of Rq ~ 1 nm

15 Absolute metrology Absolute metrology is key ingredient in freeform production chain Unique tool NANOMEFOS, developed by TNO, TU/e and NMi VSL Non-contact surface measuring, <15 nm RMS Sampling point density in practice only limited by measurement time Tens of thousands of points per minute Z R 5 mm range optical probe Metrology frame

16 Measurement result, first iteration Measurement 1 Departure from nominal surface: 345 nm RMS, 146 nm PV Good enough for bread board test error [nm] x [mm] y [mm]

17 Telescope bread board setup Goal: demonstrate performance of telescope and alignment Two mirrors, slit and rectangular aperture on rotation and tilt stages Spot profile measured by scanning stages

18 Measurement results Performance of breadboard is within budget for telescope Differences are consistent with measured surface error and expected alignment tolerances No post-alignment and no compensators are used! related to resolution related to width of slit and focal length Intensity [a.u.] Flight angle [ ] [ ] % 5 F W Swath angle [ ] simulations measurements

19 Conclusions Two-mirror freeform telescope was designed Extensive surface form tolerance analysis was performed Nominal performance 2x better than conventional telescope Manufactured using SPDT Nickel-plated Aluminium Absolute metrology using NANOMEFOS closes manufacturing loop Telescope breadboard test setup: Measured performance meets requirements No post-alignment, no-compensators! Flight model mirrors are fabricated now