AO4ELT 2

Design and Performance of Raman Fiber Amplifier Based 589-nm Guide Star Lasers for ESO VLT and Their Suitability for Future ELT AO Systems

Vladimir KARPOV — 2011-06-06T20:37:27Z

Submitted by W.R.L. Clements

Authors

V. Karpov (1), V. Protopopov (1), W. Clements (1), W. G. Kaenders (2), A .Friedenauer (2), B. Ernstberger (2), W. Hackenberg (3), D. Bonaccini Calia (3), St. A. Lewis (3)

Affiliations

(1) MPB Communications Inc., (2) TOPTICA Photonics AG, (3) Laser Systems Dept, European Southern Observatory (ESO)

Abstract

Large telescopes equipped with adaptive optics require 20-25W CW 589-nm light sources with emission linewidths of 5MHz. Towards this goal, ESO has been working for a number of years on the development of laser sources based on high-power narrow-band 1178-nm Raman fiber amplifiers (RFA) with subsequent frequency doubling to 589nm, demonstrating field tested lasers and powers beyond 50W CW. We present the design and performance of the guide star lasers being developed by industrial partners Toptica and MPBC, under contract from ESO, for deployment at the ESO VLT. The laser is designed and robustly engineered specifically for deployment on telescope facilities. The laser design is based on ESO's patented narrow-band RFA. The linearly-polarized, fiber-coupled emission of a Toptica CW diode laser, emitting 20mW at 1178nm, serves as master oscillator signal with stabilized emission frequency and controllable spectral linewidth up to a few MHz. The narrow-band seed signal is amplified in a polarization-maintaining (PM) Raman fiber amplifier developed by MPBC. The amplifier is pumped by a high-power 1120-nm PM fiber laser. With efficient suppression of stimulated Brillouin scattering, an unprecedented 40W of narrow-band RFA output has been obtained. The RFA output is then mode-matched into a resonant cavity doubler with a free spectral range exactly matching the sodium D2a to D2b separation. This allows simultaneous generation of an additional frequency component (D2b line) in the output beam to re-pump the electronic population of sodium atoms, thereby increasing the return flux. We have demonstrated doubling efficiencies >80%, resulting in CW output powers at 589nm easily exceeding the design goal of 20W. Fiber lasers provide excellent output beam quality and are turn-key, maintenance-free, reliable, ruggedized devices whose compactness allows installation directly on the launch telescope structure. They are therefore well suited for LGS applications, also considering the challenging environment of astronomical observatories.

The Four-Laser Guide Star Facility (4LGSF) for the ESO VLT Adaptive Optics Facility (AOF)

Domenico BONACCINI CALIA — 2011-06-06T20:37:24Z

submitted by D. Bonaccini

Authors

W. Hackenberg, D. Bonaccini Calia, S. Lewis, R. Holzlohner, B. Buzzoni, M. Comin, C. Dupuy, I. M. Guidolin, R. Guzman Collazos, L. Kern, M. Quattri, J. Quentin, R. Ridings, J. Argomedo, R. Arsenault, R. Conzelmann, B. Delabre, R. Donaldson, M. Downing, M. Duchateau, N. Hubin, G. Igl, L. Jochum, P. Jolley, A. Jost, M. Kiekebusch, J. Kolb, H. Kuntschner, J.-L. Lizon, M. Le Louarn, P.-Y. Madec, A. Manescau, J. Paufique, J.-F. Pirard, J. Reyes, A. Silber, C. Soenke, S. Stroebele, R. Stuik, S. Tordo, E. Vernet

Affiliations

European Southern Observatory (ESO)

Abstract

The 4LGSF is to be installed as a subsystem of the ESO Adaptive Optics Facility (AOF) on Unit Telescope 4 (UT4) of the VLT, to provide the AO systems GALACSI/MUSE and GRAAL/HAWK-I with four sodium laser guide stars. The 4LGSF will deploy four modular LGS Units at the UT4 Centrepiece. Two key aspects of the 4LGSF design are: (i) new industrial laser source (fibre lasers) with reduced volume, reduced need of maintenance, higher reliability, simpler operation and optimised spectral format for highly efficient sodium excitation, (ii) modular structure of the four LGS Units, composed of the laser and laser launch telescope, capable to operate independently of the others. The final design of the 4LGSF is now complete and the project has entered the manufacturing, assembly, integration and test phase. Furthermore, modular LGS units containing the laser emitter integrated on the launch telescope have already been demonstrated at ESO in the past years, and results will be presented. We believe that having the laser sources as an integral part of a modular unit together with the launching system offers many advantages at the system level, including the avoidance of beam relays, retaining the flexibility to use as many LGS as required independently, and the possibility of building redundancy into the system. We believe that many of these 4LGSF concepts can serve for ELT multi-LGS-assisted adaptive telescope designs and provide a valuable experience in advance of the E-ELT.

Rayleigh scattering, Fratricide effect and spot elongation: first on-sky results with GeMS

Benoit NEICHEL — 2009-02-28T23:00:00Z

Submitted by Benoit NEICHEL

Authors

B. Neichel F. Rigaut

Affiliations

Gemini Observatory

Abstract

GeMS, the Gemini MCAO system, is undergoing commissioning. Using 5 laser guide stars and a central launch, GeMS is particularly sensitive to Rayleigh backscatter and the fratricide effect. Using data covering a 5 months period, we will present results on:
Sodium return vs. Rayleigh background photons
mitigations and possible strategies to fratricide
Spot elongation measured
Benefits of fratricide for Laser Launch Telescope centering, fast acquisition procedure, cloud detection
Beam Transfer Optic design

Real-time measurement of the Na layer profile for tomographic reconstruction: experimental results and its application to the E-ELT case

Iciar MONTILLA — 2009-02-28T23:00:00Z

Submitted by Iciar MONTILLA

Authors

I. Montilla, J. P. Luke, J. G. Marichal-Hernández, M. Puga, J.M. Rodríguez-Ramos

Affiliations

Instituto de Astrofísica de Canarias, Canary Islands, Spain Universidad de La Laguna, Canary Islands, Spain

Abstract

Extremely Large Telescopes are being designed with integrated AO modules and most of their instruments will rely on them for their optimum performance. To reconstruct the wavefront we need to use Guide Stars as references, but the absence of enough Natural GSs to have a good sky coverage make it necessary the use of Laser GSs. Several technical challenges have to be solved in order to perform a good wavefront reconstruction using LGSs. In the case of Na LGSs we need to know the height at which the LGS is focused and the profile and extension of the Na layer. We propose the use of a plenoptic camera to obtain this information. The plenoptic camera was originally created to allow the capture of the Light Field, a four-variable volume representation of all rays and their directions, that allows the creation by synthesis of a 3D image of the observed object. This 3D reconstruction make it possible to retrieve the distances at which the objects are, and for this reason it is especially adequate to measure the height variations of the LGS beacons. This novel approach provides real-time information on the Na layer profile that can be introduced in the reconstruction algorithm to solve the problems derived by the spot elongation. Also we can compute at which height is focused the LGS, overcoming therefore the two challenges mentioned before. We present in this paper the laboratory results obtained with a setup simulating the laser spot and the telescope equipped with the plenoptic camera that proof that the expected height of the layers is retrieved. We also present our plans to implement on-sky tests of our system using the Na LGS of the Optical Ground Station in the Observatorio de Tenerife, and the application of this advanced concept to the E-ELT.

Gemini Multi-Conjugate Adaptive Optics (GeMS) Laser Guide Star Facility Commissioning Results

Celine DORGEVILLE — 2009-02-28T23:00:00Z

Submitted by Celine DORGEVILLE

Authors

Celine d'Orgeville et al.

Affiliations

Gemini Observatory

Abstract

The engineering and science commissioning phase of the Gemini Multi-Conjugate Adaptive Optics System (Gemini MCAO a.k.a. GeMS) project was kicked off in January 2011 when the Gemini South Laser Guide Star Facility (GS LGSF) propagated its 50W laser on the sky above the summit of Cerro Pachón, Chile. With 3 deformable mirrors, 3 Natural Guide Stars (NGS) and 5 sodium Laser Guide Stars (LGS), GeMS will be the first facility-class MCAO capability to be offered for normal science observations world-wide starting in 2012. This presentation will focus on the LGSF-side of the project and provide an overview of the LGSF subsystems, their top-level specifications, design, integration with the telescope, and current on-sky performance. Subsystems of the GS LGSF include a diode-pumped solid-state 1.06+1.32 micron sum-frequency laser producing over 50W of output power at the sodium wavelength (589nm), Beam Transfer Optics (BTO) that transport the 50W beam up the telescope, split the beam five-ways and configure the five 10W beams for projection by the Laser Launch Telescope (LLT) located behind the Gemini South 8m telescope secondary mirror, and a variety of safety systems to ensure safe laser operations for observatory personnel and equipment, neighbor observatories, as well as passing aircrafts and satellites.

ARGOS - the Laser Star Adaptive Optics for LBT

Sebastian RABIEN — 2009-02-28T23:00:00Z

Submitted by Sebastian RABIEN

Authors

S. Rabien, L. Barl, U. Beckmann, T. Blümchen, M. Bonaglia, J. L. Borelli, J. Brynnel, L. Busoni, L. Carbonaro, C. Conot, R. Davies, M. Deysenroth, O. Durney, M. Elberich, S. Esposito, V. Gasho, W. Gässler, H. Gemperlein, R. Genzel, R. Green, M. Haug, M. Lloyd Hart, P. Hubbard, S. Kanneganti, M. Kulas, J. Noenickx, G. Orban de Xivry, D. Peter, A. Quirrenbach, M. Rademacher, H. W. Rix, P. Salinari, C. Schwab, J. Storm, L. Strüder, M. Thiel, G. Weigelt, J. Ziegleder

Affiliations

Max Planck Institute für extraterrestrische Physik

Abstract

We will present the design and status of ARGOS - the Laser Guide Star adaptive optics facility for the Large Binocular Telescope. By projecting a constellation of multiple laser guide stars above each of the 8.4m primary mirrors of the LBT, ARGOS in its ground layer mode will enable a wide field adaptive optics correction for multi object spectroscopy. ARGOS implements high power pulsed green lasers and makes use of Rayleigh scattering for the guide star creation. The geometric relations of this setup in guide star height vs. primary diameter are quite comparable to an ELT with sodium guide stars. The use of LBT's adaptive secondary mirror, gated wavefront sensors, a prime focus calibration system and the laser constellation shows several aspects that may be used as pathfinding technology for the planned ELTs. In already planned upgrade steps with a hybrid Sodium-Rayleigh combination ARGOS will enable MCAO and MOAO implementations at LBT allowing unique astronomical observations.