What is MCAO…??? Why is important the knowledge of the 3D turbulence???

1. Dealing with turbulence in MCAORoberto Ragazzoni, Yazan Almomany, Carmelo Arcidiacono, Renato Falomo, Jacopo Farinato, Marco Gullieuszik, Osservatorio Astronomico di Padova (Italy);Emiliano Diolaiti, Matteo Lombini, Osservatorio Astronomico di Bologna (Italy);Alessia Moretti, Osservatorio Astronomico di Padova (Italy);Giampaolo Piotto, Univ. degli Studi di Padova (Italy);Enrico Marchetti, Robert Donaldson, European Southern Observatory (Germany);Roberto Turolla, Univ. Degli Studi di Padova (Italy)

2. What is MCAO…??? Why is important the knowledge of the 3D turbulence???

3. Turbulent layers Telescope WFS #2 #1 DM2 DM1 Atmosfera UP Multi Conjugated Adaptive Optics: MCAO

4. MCAO is a “vision” of J. Beckers in 1988 Pyramid WFS envisaged in 1995 Layer Oriented approach is shown in Backaskog 1999 and Munich 2000 LO approved as part of MAD in 2001 MCAO with 3SH and LO are on the sky in 2007! An historical perspective…

5. Canary, fall 2001

6. They take advantage of the full aperture (spot is diffraction limited on the pin of the pyramid)  Better limiting magnitude Better aliasing (larger Strehl in HO mode) It is a pupil plane WFSensor! It is “cheap” in terms of pixels usage Why pyramid..?

8. Optomechanical design Prototyping (4 stars) Glass and Alluminum Optical design

9. vWFS on MAD vs 3SH…: FoV of single stars enlarger ~0.95arcsec! LOWFS SHWFS Laboratory test in closed loop give evidence of higher limiting magnitude for the Layer Oriented WFS w.r.t the Star Oriented ~1.5 magnitude fainter

11. Basically the whole group of LO-MAD plus ESO support (3 initially, then 1) Total of 9 contiguous nights First 3 night of technical run under ESO responsibility Then 6 nights of “GTO” basically devoted to science The MAD-LO run

14. 70.5”

15. 107x107arcsec GLAO 5 NGSs Vmag tot=13.8 Here is S=10% Var. +/- 3%

20. Not a star!!!

21. A. Moretti et al.

23. We think to have material for further 3 science papers on other objects… A very productive run indeed, but…. Which is the achieved quality compared to the SO one? Which is the sky coverage one can compute given the actual performances? Any answer will be plagues by doubts about seeing, f_G, scaling laws…

24. A. Moretti et al. Omega Cen (public data) NGC6388 (LO data)

26. LayerOriented Star Oriented Layer oriented Star Oriented With an uniform “standard” reduction magnitude errors are slightly (10%) better for LO than SO, and viceversa for centroiding

28. 0.45” 0.60” 0.95”

29. 3x V=11.5

30. 3x V=12 3x V=13

31. 3x V=12 3x V=13 ~1.5mag

34. Red: estimates given in the 2002 paper Blue: left – actual measurements in the sky; right – laboratory measures

35. Red: estimates given in the 2002 paper Blue: left – actual measurements in the sky; right – laboratory measures

36. 0.70 … 0.99 0.10 … 0.25 0.07 … 0.25 ! Remember that the CCD is blue-sensitive…!!!

37. Using the Taylor hypothesys Layer Oriented “sees” the layers of turbulence so can use “several” previous measurements to estimate the coming one (not prediction, but better SNR of WFS… Areas to make MCAO with NGSs more sensitive… 2000 “Frozen” layer

38. Using non linear co-addition of stars It is well known that enlarging the FoV do not improve the correction because it is lowered the thickness of turbulence sampled… if linearly coadded!!! Areas to make MCAO with NGSs more sensitive… a 2001

39. Linear or non-linear…??? a few stars Layer you are “looking” (say 8km)

40. Linear or non-linear…??? a lot of stars Layer you are “looking” (say 8km)

41. Linear or non-linear…??? a few stars This layer is sampled Ok… Layer you are “looking” (say 8km)

42. Linear or non-linear…??? a lot of stars This layer is smoothed out!! Layer you are “looking” (say 8km)

43. Linear or non-linear…??? a lot of stars Layer you are “looking” (say 8km) Numerically averaging leads to the same trouble! + + +

44. Linear or non-linear…??? a lot of stars Layer you are “looking” (say 8km) It only goes to zero if all the WF is flatted… multiply or adding the square

45. Linear or non-linear…??? a lot of stars Layer you are “looking” (say 8km) It only goes to zero if all the WF is flatted… multiply or adding the square

46. Linear or non-linear…??? a lot of stars Layer you are “looking” (say 8km) It only goes to zero if all the WF is flatted… multiply or adding the square

47. Linear or non-linear…??? a lot of stars Layer you are “looking” (say 8km) It only goes to zero if all the WF is flatted… multiply or adding the square

48. Propagation noise is more complex… 1st DM 2nd DM Pupil plane

49. Algorithm is not conventional as the “sign” of correction is unknown A toy-model using the “bang-bang” algorithm gives a bandwidth that is at worst 2x less… There is a geometrical limit, that is about 10’ for a 42m telescope (and 25’ for a 100m one…) This makes the gain in FoV of 25 So the overall gain is in the ballpark of 12..!!!! One order of magnitude improvement in sky coverage!!! Non-linear behaviour…

50. A LO instrument started in 2002 now would produce big science NIRVANA is not optimized for deep single arm MCAO but, ok… In the timescale of a new instrument LGSs should prove their maturity (or not???) Unexplored ways to improve sensitivity include Taylor hypothesis usage and non-linear coaddition of reference stars Mixing up LGS and NGS is a safe, robust way, and there are unexplored new schemes for that Future of Layer Oriented