Potential benefits of freeform optics for the ELT instruments. J. Kosmalski

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1 Potential benefits of freeform optics for the ELT instruments J. Kosmalski Freeform Days, th October 2017

2 Summary Introduction to E-ELT intruments Freeform design for MAORY LGS Free form design for HARMONI cameras

E-ELT Intrumentations E-ELT is the 39m primary mirrortelescope of the European Southern Observatory -TMA optical with fast intermediate focus -Segmented primary 798

3 E-ELT Intrumentations E-ELT is the 39m primary mirrortelescope of the European Southern Observatory -TMA optical with fast intermediate focus -Segmented primary 798 hexagonal mirrors. -4.2m convex Secondary -3.9m tertiary concave -M4 2.4m adaptativ mirror -M5 flat elliptical 2m*2.6m FoV 10arcmin 2m at telescope focus Telescope first light in 2024

E-ELT Intrumentations 4 first light intruments:

spectrograph MAORY:Multi-conjugate Adaptive

4 E-ELT Intrumentations 4 first light intruments: METIS: Mid-infrared ELT Imager and Spectrograph HARMONI: High Angular Resolution Monolithic Optical and Near-infrared Integral field spectrograph MAORY:Multi-conjugate Adaptive Optics RelaY MICADO: Multi-AO Imaging Camera for Deep Observations

5 MAORY LGS objectiv What is Laser Tomographic AO? Stimulation of Na layer in the atmosphere Measure the WFE of each artificial star to reconstruct the atmospheric turbulence seen by the real star Problem with the design of LGS objective LGS are at finite distance, varying with the zenital angle strong defocus at thetelescope focus: VLT : between 93mm to 175mm ELT: between 2.3m and 4.65m Image Quality of the LGS is also varying with the zenital angle

6 MAORY LGS objectiv

compensate WFE is varying a lot with LGS elevation

7 MAORY LGS objectiv Aberration of the Laser Guide Stars after the transmissive dichroic: Big WFE to compensate WFE is varying a lot with LGS elevation and across the FoV LGS at 80km LGS at 160km LGS at 240km

8 MAORY LGS objectiv Specification of the LGS objectiv: Accommodate 240km to 80 km LGS focus Corrected Wavefront over 3arcmin FoV for the Wave Front Sensor F/5 output with Fixed pupil position and low pupil distorsion

9 MAORY LGS objectiv LGS Layout: 11 optical components Refocus done by moving the WFS * Dichroic not Shown

10 MAORY LGS objectiv Example of spot Diagram:

11 MAORY LGS objectiv Roughly the same performances can be achieved with only 5 Lenses and a Freeform mirror Dichroic First 2 lenses are off-axis lenses with one aspheric surface The Mirror at 45deg is freeform using only Astig and Coma.

12 MAORY LGS objectiv

13 MAORY LGS objectiv If you add one extra aspherical surface, you can even convert it into a zoom system with less 0.4% pupil diameter variation. LGS at 80km LGS at 160km LGS at 240km

14 Harmoni Camera First order parameters IR camera: Focal length 350mm, F/2.6 FoV: 20deg by 10 deg <-> Two 4k by 4k detector 60*60mm Wavelength range: microns Several spectral format Visible Camera Focal length 350mm, F/2.6 FoV: 20deg by 10 deg <-> Two 4k by 4k detector 60*60mm Wavelength range: microns Fixed spectral format

15 HARMONI IR camera - 6 Lenses design with 2 aspheric surfaces * *

16 IR Camera Perf

17 Visible Camera - 6 Lenses design with 1 aspheric surface *

18 Visible Camera Perf

19 How to make these cameras interesting for freeform optics? Make an off-axis version of the MOONS Camera! FoV 12deg by 12deg, 4k by 4k detector Focal 280 at F/0.95 Wavelength range nm Or or nm

20 Freeform IR Camera

21 No freeform (for the moment) 4 aspheric surfaces, all lenses shares a common optical axis * * * * Correction of axial color needed, the Field Lens has to be splitted.

22 Optical performances RMS spot size roughly one pixel

23 Now with freeform (astig, coma and spherical aberration) 540mm

24 Optical Performances

25 Pushing a bit 440mm More power on the corrector helps to reduces the size of the camera by 25%

26 Optical performances Image quality comparable to the nominal design without freeform

27 Freeform Visible Camera * * * Fixed format camera No correction needed of axial color Tilted detector 3 aspheric surfaces

28 Optical performances without Freeform Good image quality: below 1 pixel for 90% of the detector

29 With freeform Always below one pixel

30 Few examples have been shown that demonstrate the benefits of using freeform for some ELT instruments cases: Improved performances Less optics needed Reduction in size Conclusion ELT instruments are a perfect playground for using Freeform optics. Thanks for your attention!!

MAORY E-ELT MCAO module project overview

MAORY E-ELT MCAO module project overview Emiliano Diolaiti Istituto Nazionale di Astrofisica Osservatorio Astronomico di Bologna On behalf of the MAORY Consortium AO4ELT3, Firenze, 27-31 May 2013 MAORY