ELP-OA : status report of the setup of the demonstrator of the Polychromatic Laser Guide Star at Observatoire de Haute-Provence

Transcription

1 1 ELP-OA : status report of the setup of the demonstrator of the Polychromatic Laser Guide Star at Observatoire de Haute-Provence Renaud Foy 1,2, Nicolas Meilard 1, Michel Tallon 1, Éric Thiébaut 1, Pierre-Éric Blanc2, Michel Boër 2, Andrée Laloge 2, Auguste Le Van Suu 2, Sandrine Perruchot 2, Pierre Richaud 2, Alain Petit 3, Thierry Fusco 4 1 CRAL - Observatoire de Lyon, France 2 Observatoire de Haute-Provence, France 3 Laboratoire de Spectroscopie et de l Interaction laser-matière, DEN/DPC, CEA, France 4 DOTA - ONERA, France

2 2 Adaptive optics requires a phase reference. Isoplanatic patch : θ 2.2µm, 0.55µm If no NGS within θ = LGS = little hope to rely on NGS for the V! = Polychromatic Laser Guide Star : retrieves the tip-tilt from the LGS. ELP-OA ( Étoile Laser Polychromatique pour l Optique Adaptative ) R&D programme at OHP

3 Why do ELTs need LGS aided AO? Topic Spat. res. Range PLANETS Exoplanets 1-2 mas µm Solar System 1µm vis - ther. IR STARS AND DISKS Probing birth places 2-10 NIR 1-5 µm Normal and peculiar stars Hα Hα Chemical comp. : chronometry high nm BHs in GCs 1 mas K, CaII, vis. STARS & GALAXIES Resolved Stellar Populations DL V - K Resolved Stars in Clusters 3 mas nm Stellar Kinematic Archaeology DL V - K Intracluster Stellar Population DL J & K Cosmic SFR from SNs S 0.5 J-H-K Young, Massive Star Clusters mas >0.8 µm Black holes in GN DL 1 µm Opt. & NIR 3

4 4 PLGS principle Air refraction index : n(λ, P, T) 1 = f (λ) g(p, T) = θ λ3 = θ λ1,λ 2 (n λ3 1)/ n λ1,λ 2. (1) The tip-tilt at λ i expresses in terms of the tip-tilt difference between any two λs.

5 5 150 ns 2338 nm 4D 5/2 4P 3/2 330 nm 320 ns 1.6 M Hz 4S 1/2 3P 3/2 3P 1/2 160 ns 589 nm 16 ns 1140 nm 40 ns 2207 nm nm 32 ns 569 nm 75 ns 13 M Hz 3P 3/2 589 nm 16 ns 10 M Hz 578 nm 3S 1/2 Energy levels of neutral sodium atom.

6 6 Laser-Na interaction optimization Based on BEACON code (Bellanger et al., 2004) : resolution of optical Bloch equations. Atom model : quantum Laser field model : classical BEACON computes the density matrix evolution = f(hamiltonian(isolated atom) + hamiltonian(µ E )) Rate equation models not suitable : E t 0.

7 7 BEACON input parameters laser power density (W/cm 2 ) : 2 22W, pulse time profile : gaussian, pulse FWHM δt : variable, 40 ns, time to reach maximum peak power : 2δt, polarization : variable, circular-circular, spectral shift : function of phase modulation, phase modulation parameters : number of functions, amplitude and frequency.

8 Optimization of pulse length 8 Return flux (photon/atom/pulse/sr) 2 photon excitation of Na Gaussian pulses. Both laser beams: circular polarization, 2 sine modulation functions ns 100 ns 80 ns 60 ns 50 ns 40 ns 16 ns Power 589nm (Watt/cm 2 ) Take into account technological constraints : P and F R not easily tunable, efficiency of dyes. Also : spot characteristics,... 2-photon excitation is a non linear process!!

9 Modulation function 9 2 photon excitation of Na: return flux at 330 nm Intensity at 589 and at 569 nm : 1 W/cm 2 Photon/atom/pulse/sr Pulse length (ns) Backscattered flux at 330 nm versus pulse length. Black dots : an optimized phase modulation fuction. Red crosses : modulation used for PASS-2 experiment at CEA/Pierrelatte.

10 Is this return flux large enough? σ(θ) FWHM/ N Answer # 1 : with a classical projector, NO Increasing the projector diameter produces speckle noise. If AO precompensates for the upward beam = saturation of Na absorption. No benefit! Answer # 2 : with an interferometric projector, YES Cramér-Rao criterion : σ(θ) limited not by FWHM but by the smallest resolved features in the laser spot image, as produced by e.g. 3 aperture interferometer producing a pattern in the mesosphere. 10

11 Specs of the interferometric projector 11 fringe pattern > λ/d nm no speckle : single aperture diameter d < r 0 pattern translation invariant = at most 1 phase closure relation = at most 3 apertures need of an AO at the master telescope focus, down to 330 nm no center of gravity = 2 and soon 3D crosscorrelations

12 Figure 1 : Projecteur in pupil plane Figure 7 : Laser guide star image by telescope pli, pup_proj_569 pli, tel_569_tab(1,,) Figure 9 : Criterion function

13 Strehl ratio produced by BOA (ONERA) at 330nm 13

14 End-to-end model Inputs : Lasers : P, F R, modulation, polarization... Projector : pupil function, transmission ( 80%) Atmosphere : Kolmogorov phase screen, transmission (80%) Mesosphere : Na column density ( atoms/m 2 ), altitude (92 km) Atmosphere : Kolmogorov phase screen, 330nm, 2.3µm) Master telescope : pupil, transmission ( 77%) Adaptive optics : Strehl ratio, transmission Detector : EMCCD, ρ %, ρ % Data processing : phase restoration or cross correlations 14

15 15 Interferometric projector optimization See also poster Meilard et al. 550 nm ELP OA interferometric projector <P 589> = <P 569> = 22 W at the mesosphere r 0 = 10cm. Baseline = 80 cm. 3 apertures Aperture diameter (cm) 550 nm ELP OA interferometric projector <P 589> = <P 569> = 22 W at the mesosphere r 0 = 10cm. Aperture diameter = 5 cm. 3 apertures Baseline (cm)

16 Goal S tilt nm 16

17 Ongoing construction of the demonstrator ELP-OA layout Mesosphere Mesosphere 17 GSM seeing monitor Telescope m Transport OHP Seismometer Adaptive Optics Laser chains nm Tilt Tip tilt mirror 569 nm Science Measurement Vibrations corrections channel nm Tilt correction green / red FOCAL INSTRUMENTATION Beams Launch telescope Seismometer Na monitor telescope

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20 20 Auxiliary equipments : GSM from Nice Na monitor, from 1.2m telescope

21 Time schedule Laser rooms commissioning July NdYAGs pump lasers delivered August 2009 integration of dye circulators end on January 2010 laser chains integration end on April 2010 beam transport to the dome end on April 2010 first launch at the mesosphere end April 2010 full experiment

22 22 Analysis and roadmap from the ELT Adaptive Optics Working Group (2006)... the polychromatic LGS development should be monitored and as for other novel concepts proposed in this document encouraged. Should the pending theoretical issues and simulations be positive, it should be encouraged for on-sky demonstration. Acknowledgments : ANR, PACA Region, DGA, CNRS/INSU