Ground-based optical astronomical observations supported by or in the vicinity of laser guide-star systems can be contaminated by Raman-scattered laser photons. Anticipating, alleviating, and ...correcting for the impact of this self-inflicted contamination requires a detailed knowledge of the pure-rotational and rotational-vibrational spectrum of the molecules in our atmosphere. We present a 15.3-hr-deep combined spectrum of the 4LGSF's 589 nm≈509 THz sodium laser beams of Paranal observatory, acquired with the ESPRESSO spectrograph at a resolution λ/Δλ≅140000≈0.12 cm^{−1} and an altitude of 23 km above mean sea level. We identify 865 Raman lines over the spectral range of 3770; 7900 Å≈ +9540; –4315 cm^{−1}, with relative intensities spanning ∼5 orders of magnitudes. These lines are associated to the most abundant molecules of dry air, including their isotopes: ^{14}N^{14}N, ^{14}N^{15}N, ^{16}O^{16}O, ^{16}O^{17}O, ^{16}O^{18}O, and ^{12}C^{16}O^{16}O. The signal-to-noise of these observations implies that professional observatories can treat the resulting catalog of Raman lines as exhaustive (for the detected molecules, over the observed Raman shift range) for the purpose of predicting/correcting/exploiting Raman lines in astronomical data. Our observations also reveal that the four laser units of the 4LGSF do not all lase at the same central wavelength. We measure a blueshift of +43±10 MHz ≅−50∓10 fm with respect to λ_{*}=5891.59120 Å for LGSU1/2, and +94±10 MHz ≅−109∓10 fm for LGSU3/4. These offsets, including the difference of ∼50 MHz between LGSU1/2 and LGSU3/4, are larger than the observed 4LGSF spectral stability of ±3 MHz over hours. They remain well within the operational requirements for creating artificial laser guide-stars, but hinder the assessment of the radial velocity accuracy of ESPRESSO at the required level of 10 m s^{−1}. Altogether, our observations demonstrate how Raman lines can be exploited by professional observatories as highly-accurate, on-sky wavelength references.
Laser guide stars employed at astronomical observatories provide artificial wavefront reference sources to help correct (in part) the impact of atmospheric turbulence on astrophysical observations. ...Following the recent commissioning of the 4 Laser Guide Star Facility (4LGSF) on Unit Telescope 4 (UT4) of the Very Large Telescope (VLT), we characterize the spectral signature of the uplink beams from the 22-W lasers to assess the impact of laser scattering from the 4LGSF on science observations. We use the Multi-Unit Spectroscopic Explorer (MUSE) optical integral field spectrograph mounted on the Nasmyth B focus of UT4 to acquire spectra at a resolution of R≅3000 of the uplink laser beams over the wavelength range of 4750 Å–9350 Å. We report the first detection of laser-induced Raman scattering by N2 , O2 , CO2 , H2O , and (tentatively) CH4 molecules in the atmosphere above the astronomical observatory of Cerro Paranal. In particular, our observations reveal the characteristic spectral signature of laser photons—but 480 Å to 2210 Å redder than the original laser wavelength of 5889.959 Å—landing on the 8.2-m primary mirror of UT4 after being Raman-scattered on their way up to the sodium layer. Laser-induced Raman scattering, a phenomenon not usually discussed in the astronomical context, is not unique to the observatory of Cerro Paranal, but it is common to any astronomical telescope employing a laser guide star (LGS) system. It is thus essential for any optical spectrograph coupled to a LGS system to thoroughly handle the possibility of a Raman spectral contamination via a proper baffling of the instrument and suitable calibrations procedures. These considerations are particularly applicable for the HARMONI optical spectrograph on the upcoming Extremely Large Telescope (ELT). At sites hosting multiple telescopes, laser-collision-prediction tools should also account for the presence of Raman emission from the uplink laser beam(s) to avoid the unintentional contamination of observations acquired with telescopes in the vicinity of a LGS system.
Ground-based optical telescopes, in particular large ones, require adaptive optics to overcome the atmospheric seeing limit due to turbulence. Correcting the distorted wavefront necessitates bright ...stars in the field of view. The sky coverage can be greatly increased by using artificial sodium laser guide stars in addition to natural guide stars. We describe the underlying physics and technical considerations relevant to such systems before discussing the design of the four-laser guide star facility (4LGSF) which is currently under development for the ESO Very Large Telescope (VLT) on Cerro Paranal, Chile. The focus is upon the justification of the requirements and their technical solution.
The first observations of laser guide-star photons that are Raman-scattered by air molecules above the Very Large Telescope (VLT) were reported in June 2017. The initial detection came from the ...Multi-Unit Spectroscopic Explorer (MUSE) optical integral field spectrograph, following the installation of the 4 Laser Guide Star Facility (4LGSF) on Unit Telescope 4 (UT4) of the VLT. In this Letter, we delve further into the symbiotic relationship between the 4LGSF laser guide-star system, the UT4 telescope, and MUSE by monitoring the spectral contamination of MUSE observations by Raman photons over a 27-month period. This dataset reveals that dust particles deposited on the primary and tertiary mirrors of UT4, which are responsible for a reflectivity loss of ∼8% at 6000 Å, contribute (60 ± 5)% to the laser line fluxes detected by MUSE. The flux of Raman lines, which contaminates scientific observations that are acquired with optical spectrographs, thus provides a new, non-invasive means to monitor the evolving scatter properties of the mirrors of astronomical telescopes that are equipped with laser guide-star systems.
Zusammenfassung
UNIT (Universal Iterative Template) ist eine gemeinsame Initiative der Volkswagen-Konzern-IT und Konzernlogistik mit dem Ziel der Prozess- und Systemstandardisierung im Unternehmen. ...Das UNIT-Template wird bereits heute weltweit in vielen neuen Komponenten- und Fahrzeugmontagewerken des Volkswagen-Konzerns eingesetzt. Es unterstützt innovative Logistikprozesse für Produktionsgesellschaften und stellt die Integration vieler weiterer Bereiche, wie zum Beispiel der Finanz, sicher.
Das prozessorientierte Template UNIT unterstützt die Fachbereiche bei der Umsetzung einheitlicher Geschäftsprozesse an den Standorten des Volkswagen-Konzerns. Durch die modulare Struktur von UNIT profitieren Werke weltweit von Prozessinnovationen. Dadurch sinkt der konzernweite Aufwand für die Erstellung von IT-Systemen.
2D van der Waals solids (vdW) have received attention for decades, due to their unique anisotropic mechanical character, making them useful in applications such as lubricants and pencils. But their ...anisotropy is not limited only to mechanical properties; rather it extends by default to all physical properties, making vdW solids interesting candidates for applications in fields as varied as catalysis and electronics. Here, we explore nanostructures of group V transition metal dichalcogenides (TMDs), a family of vdW solids, NbS2 and TaS2. We develop new vapor-phase bottom-up synthetic routes for nanosheet and nanotube variants. Furthermore, we discover their anisotropy-resulting self-optimizing behavior as hydrogen evolution catalysts, opening a new area of research.
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