Activities of the ESO LGS Group

Transcription

1 Activities of the ESO LGS Group Ronald Holzlöhner, Domenico Bonaccini Calia, Yan Feng, Wolfgang Hackenberg, Luke Taylor Laser Guide Star Department European Southern Observatory (ESO) Garching near Munich, Germany 1

2 ESO LGS Department Tasks Deliver a single LGS on VLT-UT4 and run it with Sinfoni and NAOS Prepare, design and implement a 4-LGS Facility, 2 nd Gen VLT Instruments Define, R&D and transfer to industry the lasers for MCAO and EELT Technological Developments: fiber lasers, PCF fibers, high power modulators Explore novel laser propagation/sensing schemes Contribute to the EELT LGS facility definition Talk at Ringberg 29Oct Telescope Systems Division LGS Dept Ronald Holzlöhner

3 VLT at Cerro Paranal: LGSF project ESO, MPE, MPIA Now operational on UT4 with NACO and Sinfoni Clean room with PARSEC dye laser (MPE) Single-mode PCF beam relay (27.5m, 14.5µm MFD) 50 cm f/1 carbon fiber Launch Telescope Precious LGS-AO experience Maintenance requirements demanding Will accumulate useful Na data for future systems Optimizations of the LGS-AO possible

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5 One LGS-AO system is operational at VLT now

6 Physical Optics Simulation of LGS Propagation Physical optics simulations of LGS propagation and imaging in the planned GRAAL wavefront sensor (WFS) Motivation: Deep in far-field regime; moreover λ à l 02 /L (l 0 : smallest eddy diameter, L: propagation distance) We model different launch telescopes (LTs) with realistic aberrations, the turbulent atmosphere, a sodium layer of finite thickness, the downlink propagation of the return light, the VLT, and finally the 7x7 NACO or 40x40 GRAAL WFS We study both long-exposure and instantaneous images and compute spot size statistics Results agree with observation and enable us to optimize the LT diameter and devise design rules. 6

7 Simulate LGS Propagation LGS on the Mesosphere: Physical Optics Propagation Simulations are needed to deal with the LGS images See poster No Atmosphere, only LT With atmosphere (s = 0.77) WFS, 0.8s, 1.12 fwhm

8 Spot Size on Guider: Observation vs. Simulation See poster LGS FWHM: Spec is 1.25 at 0.7 seeing at WFS LT trefoil accounts for 0.2 At guider, VLT depth of focus counts Zenith dependence ~0.15 LT sensitive to temperature variation Need to optimize WFS scale for LGS

9 Field Results I Throughput: BRSI (beam relay system) 83% M 2 = 1.3 PCF Fibre: 63% Fibre Throughput Fibre Throughput vs Beam M2 Total throughput: 55% Up to 5.8W in air achieved Throughput stability needs improvement Diffraction-limited output wins on losses M-square values PARSEC was built by MPE (S. Rabien, R. Davis et al.)

10 Field Results II Flux: m V = 8.5 (avg sodium night) 53.8 phot/s/cm 2 /W Sinfoni WFS Throughput: 19.5% NACO WFS Throughput: 34% Spec: 1x10 6 cts/s/m 2, hence ~2.5W sufficient this night Return efficiency very good We want more power emitted

11 Strategic R&D: fibre lasers Why Sodium Guide-Star Fibre Lasers? Sodium LGSs allow better AO performance and CW operation Fibre laser offer the ultimate design solution, because they are Compact (rack-mounted) Efficient (low power consumption) Robust & reliable (availability of key components from telecom industry) Safe (all-solid state, no chemicals) Alignment free (turnkey operation) Built-in in fibre delivery Diffraction-limited output Power scalable (e.g. by multiplexing) Upgradeable to pulsed operation Low-priced

12 Strategic R&D: fiber lasers These are the sources for the AOF/4LGSF multiple lasers; for EELT it is TBC a 10 15W fiber laser at 589nm mitigates also the beam relay to LT problem So far 5.2W at 589nm has been obtained with PPKTP, via SHG of 1178nm Now working on narrowing the 1178nm line. 4 W <12MHz linewidth obtained at 1178nm We have produced 14W < 200 MHz linewidth at Limiting factor: SBS Next step: reach 25W 1178nm <200 MHz In parallel we are looking at new bismuth-doped fibers which lase at 1178nm (FORC/Moscow) We have ~5 SHG crystals (PPSLT )to test still

13 VLT AO Facility 1170 actuators in DSM GRAAL/Hawk-I I 7 7 FOV imager, 0.1 /pxl, near IR / GLAO correction GALACSI/MUSE integral field visible spectrometer. GLAO (60 field) or MCAO (15 field) CASIS LGS assisted

14 4 Laser Guide Stars Facility 4 LGS, off axis up to Mphot/sec/m 2 LGS FWHM <1.2 on WFS Central LGS also operational 4LT mounted on UT4 Centerpiece Will Serve 2 nd Gen AO systems on UT4 Galacsi-MUSE and GRAAL-HawkI PDR in Jan 2008 Commissioning in (TBC) LGS fixed on pupil

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16 Unique design aspects of 4LGSF: Rack-mounted 15-W fiber laser systems in the direct vicinity of each laser launch telescope 6 field selection by tilting the 30-cm laser launch telescope Shield of scattering up to the top ring LTS units modular Service mostly in the integration room LRU concept for LTS (line replacement) 16

17 Summary LGSF now operational Performance data collection and fine tuning ongoing LGS Dept working hand-in-hand with AO Dept on AOF AOF/4LGSF project reaching PDR level Development of fiber lasers Work on EELT for the definition of LGS facility / lasers requirements 17

18 Simulation Flow 90 km 7 sodium slices save weighted intensities in each slice LGS: compute PSF for each slice or: NGS 10 phase screens m 2 LTS Uplink VLT, 8m convolve LGS intensities with PSF, sum up Downlink 18

19 AO Top Level Requirements Visible light operation: ~ µm, 0.2 /pix Very deep exposures (80 h) NGSs in Scientific FOV forbidden! Statistically BAD seeing (1.1 ) High sky coverage required Wide and Narrow Field Modes: Seeing enhancement over 1 FOV (2xEE vs seeing) Diffraction 750 nm over ~10 FOV 15-16/03/04 for p.19 MUSE UT4 AOF/4LGSF

20 GLAO functional block diagram WFS Calibration Pupil MUSE + AO Calibration LGSs Pupil MUSE SPECTROGRAPH MUSE Calibration Field FOV 4 LGS Wavefront sensors LGS Focus Trombone 3 FOV AO RELAY OPTICS VLT ADAPTER M2 + DM Laser Launch Telescopes 2 LGS Acquisition Camera On-axis IR NGS TT Sensor Off-axis Vis NGS TT Sensor VLT M /03/04 p.20