On ESO LGS activities Domenico Bonaccini Calia, Yan Feng, Wolfgang Hackenberg, Ronald Holzlöhner, Luke Taylor Laser Guide Star group European Southern Observatory (ESO) Garching near Munich, Germany 1

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

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One LGS-AO system is operational at VLT now LGS FWHM: Spec is 1.25” at 0.7” seeing at WFS LT trifoil accounts for 0.2” At guider, VLT depth of focus cts Zenith dependence ~0.15” LT sensitive to T variation Need to dimension WFS scale to LGS LGS on the Mesosphere: No Atmosphere, only LT With atmosphere WFS, 0.8s, 1.12” fwhm Physical Optics Propagation Simulations are needed to deal with the LGS images See poster

Physical Optics Simulation of LGS Propagation Physical optics simulations of LGS propagation and imaging in the planned GRAAL wavefront sensor (WFS) Motivation: Deep in near-field regime; moreover λ  l 0 2 /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. 5

Field Results Throughput: BRSI 83% M2=1.3 PCF Fibre Throughput 63% Total throughput to air 55% Up to 5.8W in air achieved Throughput stability needs improvement Diffraction limited output wins on losses Flux: mV= phot/s/cm2/W Sinfoni WFS Throughput 19.5% NACO WFSThroughput 34% Return efficiency very good We want more power emitted

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)  In-built fibre delivery  Diffraction-limited output  Power scalable (e.g. by multiplexing)  Upgradable to pulsed operation  Low-priced  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)  In-built fibre delivery  Diffraction-limited output  Power scalable (e.g. by multiplexing)  Upgradable to pulsed operation  Low-priced Strategic R&D: fibre lasers

Strategic R&D: fiber lasers These are the source for the AOF/4LGSF multiple lasers; for EELT it is TBC a 10-15W fiber laser at 589nm solves also the beam relay to LT problem So far 5.2W at 589nm have been obtained with PPKLT, via SHG of 1178nm We are now working on narrowing the 1178nm line. 4 W <12MHz linewidth obtained at 1178nm Raman amplification needs to control SBS. We have produced 14W < 200 MHz linewidth at 1178 Next step in these coming months, on sight is to reach 25W 1178nm <200 MHz In parallel we are looking at the new Bismuth fibers which lases at 1178nm, with FORC/Moscow We have ~5 SHG crystals (PPSLT )to test still

4 Laser Guide Stars Facility 4 LGS, off axis up to 330” 2.5 – 5 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

10 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

Summary 11 LGSF now operational Performance data collection and fine tuning ongoing AOF/4LGSF project reaching PDR level Developments running for fiber lasers Work on EELT for the definition of LGS facility / lasers requirements