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295:(VLT), as a new subsystem of the Adaptive Optics Facility (AOF). The 4LGSF is a complement of the VLT Laser Guide Star Facility (LGSF). Instead of a single laser beam, the 4LGSF propagates four laser beams into the skies of Paranal, in northern Chile, producing four artificial stars by illuminating sodium atoms located in the atmosphere at 90 km altitude. These four stars enable getting a better correction in a specific direction, or widening the field of view corrected by an adaptive optics. Each laser delivers 22 watts in a diameter of 30 cm (12 in). The 4LGSF Laser System is based on a fiber Raman laser technology, developed at ESO and transferred to industry.
311:
vector of the atom), decreases the atomic fluorescence of the laser guide star by changing the angular momentum of the atom before a two-level cycling transition can be established through optical pumping with circularly polarized light. Recoil from spontaneous emission, resulting in a momentum kick to the atom, causes a redshift in the laser light relative to the atom, rendering the atom unable to absorb the laser light and thus unable to fluoresce. Transition saturation is the depopulation of atoms from a state of higher angular momentum (F=2) to a state of lower angular momentum (F=1), resulting in a different absorption wavelength.
32:
208:
195:
applications include sum-frequency-mixed solid-state lasers. New third generation laser systems based on tunable diode lasers with subsequent narrow-band Raman fiber amplification and resonant frequency conversion have been under development since 2005. Since 2014 fully engineered systems are commercially available. Important output features of the
108:. However, this star can be much fainter than is required for natural guide star adaptive optics because it is used to measure only tip and tilt, and all higher-order distortions are measured with the laser guide star. This means that many more stars are suitable, and a correspondingly larger fraction of the sky is accessible.
307:, which will have a similar system to support the adaptive optics of the telescope. Given its power, the 4LGSF operations follow a protocol to avoid any risk. The laser system is equipped with an automatic aircraft avoidance system that shuts down the lasers if an aircraft ventures too close to the beams.
298:
The upgrade to four lasers with fiber Raman laser technology is necessary to support the new instruments at
Paranal Observatory, like HAWK-I (with GRAAL) and MUSE (with GALACSI). Also with the 4LGSF the stability is increased, the amount of preventative maintenance support and the preparation of an
182:
of light by the molecules in the lower atmosphere. In contrast to sodium beacons, Rayleigh beacons are much simpler and less costly, but do not provide as good a wavefront reference, since the artificial beacon is generated much lower in the atmosphere. The lasers are often pulsed, with measurement
194:
were the first laser sources used in laser guide star applications. These tunable lasers have continued to play a significant role in this field. However, the use of fluid gain media has been considered by some researchers as disadvantageous. Second generation laser sources for sodium guide star
310:
For sodium laser guide stars, there are three main challenges to overcome: Larmor precession, recoil, and transition saturation. Larmor precession, which is the precession of the sodium atom in the geomagnetic field (precisely, it is the precession of the quantized total atomic angular momentum
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of the atmosphere being time-gated (taking place several microseconds after the pulse has been launched, so that scattered light at ground level is ignored and only light that has traveled for several microseconds high up into the atmosphere and back is actually detected).
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Laser guide star adaptive optics is still a very young field, with much effort currently invested in technology development. As of 2006, only two laser guide star AO systems were regularly used for science observations and have contributed to published results in
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does not move around in the sky as astronomical sources do. In order to keep astronomical images steady, a natural star nearby in the sky must be monitored in order that the motion of the laser guide star can be subtracted using a
76:. Natural stars can serve as point sources for this purpose, but sufficiently bright stars are not available in all parts of the sky, which greatly limits the usefulness of natural guide star adaptive
212:
416:
Primmerman, Charles A.; Murphy, Daniel V.; Page, Daniel A.; Zollars, Byron G.; Barclay, Herbert T. (1991). "Compensation of atmospheric optical distortion using a synthetic beacon".
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at an altitude of around 90 km (56 mi). The sodium atoms then re-emit the laser light, producing a glowing artificial star. The same atomic transition of sodium is used in
967:
D. Bonaccini Calia D. Budker J. M. Higbie W. Hackenberg R. Holzlohner, S. M. Rochester. Optimization of CW sodium laser guide star efficiency. Astronomy and
Astrophysics, 510, 2010.
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Wizinowich, Peter L.; Le
Mignant, David; Bouchez, Antonin H.; Campbell, Randy D.; Chin, Jason C. Y.; Contos, Adam R.; Van Dam, Marcos A.; Hartman, Scott K.; et al. (2006).
459:
Bass, Isaac L.; Bonanno, Regina E.; Hackel, Richard P.; Hammond, Peter R. (1992). "High-average-power dye laser at
Lawrence Livermore National Laboratory".
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The sodium laser guide star for use in adaptive optics to correct for atmospheric distortions is believed to have been invented by
Princeton physicist
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observing run time will be considerably reduced compared to the LGSF, which currently still uses its original dye laser (planned to be replaced by a
19:
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having tested lasers on the sky but not yet achieved regular operations. Other observatories developing laser AO systems as of 2006 include the
88:. Light from the beam is reflected by components in the upper atmosphere back into the telescope. This star can be positioned anywhere the
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682:
121:
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Four generations of sodium guide star lasers for adaptive optics in astronomy and space situational awareness
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995:
1015:
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High average power laser gain medium with low optical distortion using a transverse flowing liquid host
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265:
152:
There are two main types of laser guide star system, known as sodium and
Rayleigh beacon guide stars.
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857:
786:"Free from the Atmosphere – Laser Guide Star System on ESO's VLT Starts Regular Science Operations"
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264:. However, laser guide star systems were under development at most major telescopes, with the
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Markus Kasper; Stefan
Stroebele; Richard Davies; Domenico Bonaccini Calia (13 June 2007).
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Since April 2016, the 4 Laser Guide Star
Facility (4LGSF) has been installed at the ESO's
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mentioned here include diffraction-limited beam divergence and narrow-linewidth emission.
8:
840:"Very Large Telescope – The world's most advanced visible-light astronomical observatory"
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The actual laser guide star is the small spot above the apparent end of the laser beam.
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desires to point, opening up much greater amounts of the sky to adaptive optics.
51:
552:
985:
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592:"The W. M. Keck Observatory Laser Guide Star Adaptive Optics System: Overview"
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Everett, Patrick N. (1989). "300-Watt dye laser for field experimental site".
1004:
979:
948:"The European Extremely Large Telescope – The world's biggest eye on the sky"
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508:(2001). "Multiple-Return-Pass Beam Divergence and the Linewidth Equation".
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One of the launch telescopes for the VLT Four Laser Guide Star
Facility.
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89:
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553:"Efficient modeless laser for a mesospheric sodium laser guide star"
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Gemini's Laser Vision
Reveals Striking New Details in Orion Nebula
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is deflected by astronomical seeing on the way up, the returning
80:. Instead, one can create an artificial guide star by shining a
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Sodium beacons are created by using a laser tuned to 589.2
44:
699:"SodiumStar 20/2 – High Power CW Tunable Guide Star Laser"
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Comaskey, Brian; Ault, Earl; Kuklo, Thomas (Nov 6, 2003),
958:
379:
Proceedings of the International Conference on Lasers '88
726:
458:
599:
Publications of the Astronomical Society of the Pacific
303:). The 4LGSF helps astronomers to test devices for the
894:"Laser Guide Star Units Accepted and Shipped to Chile"
729:"Laser Guide Star Adaptive Optics: Present and Future"
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started regular scientific operations in June 2007.
661:. Adaptive Optics Systems V. Vol. 9909. SPIE.
631:
1002:
912:"HAWK-I – High Acuity Wide-field K-band Imager"
551:Pique, Jean-Paul; Farinotti, Sébastien (2003).
991:ESO’s New Compact Laser Guide Star Unit Tested
550:
504:
131:sodium laser of the Adaptive Optics Facility
557:Journal of the Optical Society of America B
68:). Adaptive optics (AO) systems require a
930:"MUSE – Multi Unit Spectroscopic Explorer"
834:
832:
353:"VLT's New Laser Launchers Arrive at ESO"
986:ESOcast 34: How To Stop a Star's Twinkle
220:Example of an artificial reference star.
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30:
23:Powerful laser guide star system at the
18:
16:Artificial star image used by telescopes
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284:. The laser guide star system at the
244:scientific literature: those at the
54:systems, which are employed in large
876:"ESO Signs Technology Transfer Deal"
733:Very High Angular Resolution Imaging
500:
498:
328:"Powerful New Laser Passes Key Test"
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727:Olivier, S. S.; Max, C. E. (1994).
72:reference source of light called a
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816:European Southern Observatory
657:; Fetzer, Gregory J. (2016).
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178:Rayleigh beacons rely on the
753:10.1007/978-94-011-0880-5_48
230:Strategic Defense Initiative
62:distortion of light (called
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202:
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812:"Four Lasers Over Paranal"
266:William Herschel Telescope
278:Large Binocular Telescope
159:to energize atoms in the
47:image created for use in
282:Gran Telescopio Canarias
228:in 1982, as part of the
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577:10.1364/JOSAB.20.002093
708:. TOPTICA Photonics AG
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36:
28:
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1011:Astronomical imaging
530:10.1364/AO.40.003038
481:10.1364/AO.31.006993
293:Very Large Telescope
286:Very Large Telescope
270:Very Large Telescope
58:in order to correct
745:1994IAUS..158..283O
667:2016SPIE.9909E..0RD
655:D'Orgeville, Céline
611:2006PASP..118..297W
569:2003OSAJB..20.2093P
522:2001ApOpt..40.3038D
473:1992ApOpt..31.6993B
430:1991Natur.353..141P
387:1989lase.conf..404E
65:astronomical seeing
25:Paranal Observatory
1016:Laser applications
790:ESO for the public
675:10.1117/12.2234298
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169:sodium-vapor lamps
127:The first 22-watt
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982:@ keck.hawaii.edu
858:"Adaptive Optics"
762:978-0-7923-2633-5
467:(33): 6993–7006.
252:Observatories in
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95:Because the
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49:astronomical
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362:22 February
301:fiber laser
226:Will Happer
101:laser light
60:atmospheric
1005:Categories
641:2016-03-19
315:References
256:, and the
254:California
234:classified
192:Dye lasers
180:scattering
165:mesosphere
157:nanometers
97:laser beam
86:atmosphere
74:guide star
56:telescopes
771:115762227
381:: 404–9.
90:telescope
84:into the
70:wavefront
821:27 April
538:18357323
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395:20243203
203:Progress
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663:Bibcode
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446:4281137
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337:2 April
250:Palomar
163:of the
129:TOPTICA
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418:Nature
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262:Hawaii
78:optics
792:. ESO
767:S2CID
702:(PDF)
595:(PDF)
442:S2CID
305:E-ELT
112:Types
82:laser
823:2016
798:2011
757:ISBN
714:2019
679:ISBN
534:PMID
485:PMID
399:OSTI
391:OCLC
364:2012
339:2014
280:and
272:and
248:and
246:Lick
171:for
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