ARAL: a facility to fuel VLTI instruments with photons

Morel, S.; Vannier, M.; Ménardi, Serge; Biancat-Marchet, Fabio; Fischer, Michael; Gitton, Philippe B.; Glindemann, Andreas; Guisard, Stéphane; Haddad, N.; Housen, Nico; Huxley, Alexis; Kiekebusch, M.; Longinotti, Antonio; Duc, Thanh Phan; Schoeller, Markus; Wallander, Anders

doi:10.1117/12.550175

Cited by 4 publications

(3 citation statements)

References 5 publications

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“…It generates four nearinfrared beams, each covering the J-, H-, and K-bands, using wavefront division (in contrast to the former unit which used amplitude division), providing a better control of spectrum, spatial coherence, and polarisation state (Morel et al 2004). This unit was previously used in the testbed (Sahlmann 2007) and is usually powered by a black body light source.…”

Section: Calibration Source and Laser Metrologymentioning

confidence: 99%

The PRIMA fringe sensor unit

Ménardi¹,

Abuter²,

Accardo³

et al. 2009

A&A

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Context. The fringe sensor unit (FSU) is the central element of the phase referenced imaging and micro-arcsecond astrometry (PRIMA) dual-feed facility and provides fringe sensing for all observation modes, comprising off-axis fringe tracking, phase referenced imaging, and high-accuracy narrow-angle astrometry. It is installed at the Very Large Telescope Interferometer (VLTI) and successfully served the fringe-tracking loop during the initial commissioning phase. Aims. To maximise sensitivity, speed, and robustness, the FSU is designed to operate in the infrared K-band and to include spatial filtering after beam combination and a very-low-resolution spectrometer without photometric channels. It consists of two identical fringe sensors for dual-star operation in PRIMA astrometric mode. Methods. Unique among interferometric beam combiners, the FSU uses spatial phase modulation in bulk optics to retrieve real-time estimates of fringe phase after spatial filtering. The beam combination design accommodates a laser metrology for pathlength monitoring. An R = 20 spectrometer across the K-band makes the retrieval of the group delay signal possible. The calibration procedure uses the artificial light source of the VLTI laboratory and is based on Fourier transform spectroscopy to remove instrumental effects. Results. The FSU was integrated and aligned at the VLTI in July and August 2008. It yields phase and group delay measurements at sampling rates up to 2 kHz, which are used to drive the fringe-tracking control loop. During the first commissioning runs, the FSU was used to track the fringes of stars with K-band magnitudes as faint as m K = 9.0, using two VLTI auxiliary telescopes (AT) and baselines of up to 96 m. Fringe tracking using two Very Large Telescope (VLT) unit telescopes was demonstrated. Conclusions. The concept of spatial phase-modulation for fringe sensing and tracking in stellar interferometry is demonstrated for the first time with the FSU. During initial commissioning and combining stellar light with two ATs, the FSU showed its ability to improve the VLTI sensitivity in K-band by more than one magnitude towards fainter objects, which is fundamental for achieving the scientific objectives of PRIMA.

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Section: Calibration Source and Laser Metrologymentioning

confidence: 99%

The PRIMA fringe sensor unit

Ménardi¹,

Abuter²,

Accardo³

et al. 2009

A&A

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“…Longitudinal pupil tracking performance is characterized at the VLTI laboratory by injecting artificial light source beams into the GRAVITY instrument via the delay lines, using the ARAL facility (Morel et al 2004). The longitudinal pupil shifts are simulated by manipulating the delay line variable curvature positions.…”

Section: The Pupil Tracker Characterisationmentioning

confidence: 99%

Methods for multiple-telescope beam imaging and guiding in the near-infrared

Anugu

Amorim

Gordo

et al. 2018

Monthly Notices of the Royal Astronomical Society

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Atmospheric turbulence and precise measurement of the astrometric baseline vector between any two telescopes are two major challenges in implementing phase referenced interferometric astrometry and imaging. They limit the performance of a fibre-fed interferometer by degrading the instrument sensitivity and astrometric measurements precision and by introducing image reconstruction errors due to inaccurate phases. A multiple beam acquisition and guiding camera was built to meet these challenges for a recently commissioned four beam combiner instrument, GRAVITY, at the ESO Very Large Telescope Interferometer. For each telescope beam it measures: a) field tip-tilts by imaging stars in the sky; b) telescope pupil shifts by imaging pupil reference laser beacons installed on each telescope using a 2 × 2 lenslet; c) higher order aberrations using a 9 × 9 Shack-Hartmann. The telescope pupils are imaged for a visual monitoring while observing. These measurements enable active field and pupil guiding by actuating a train of tip-tilt mirrors placed in the pupil and field planes, respectively. The Shack-Hartmann measured quasi-static aberrations are used to focus the Auxiliary Telescopes and allow the possibility of correcting the non-common path errors between the Unit Telescopes adaptive optics systems and GRAVITY. The guiding stabilizes light injection into single-mode fibres, increasing sensitivity and reducing the astrometric and image reconstruction errors. The beam guiding enables to achieve astrometric error less than 50 µas. Here, we report on the data reduction methods and laboratory tests of the multiple beam acquisition and guiding camera and its performance on-sky.

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“…Next to MIDI and AMBER, the VLTI includes a large number of complex subsystems, including adaptive optics on the UTs (MACAO, Arsenault al 2003), a visible tip-tilt corrector for the ATs (STRAP, Bonaccini al 1997), six delay lines (Hogenhuis et al 2003), an H-band fringe tracker (FINITO, Gai et al 2004), an IR tip-tilt corrector in the underground laboratory (IRIS, Gitton et al 2004), a reference source (ARAL, Morel et al 2004). The lab itself, now quite crowded, is schematically shown in Fig.…”

Section: An Introduction To the Vltimentioning

confidence: 99%

The VLT Interferometer

Richichi

2007

Proc. IAU

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The ESO Very Large Telescope Interferometer (VLTI) is arguably the most powerful optical interferometric facility available at present. In addition to the wide choice of baselines and the light collecting power of its 8.2 m and 1.8 m telescopes, the VLTI also offers a smooth and user-friendly operation which makes interferometry accessible to any astronomer and covers a wide range of scientific applications. Behind the routine scientific operations, however, the VLTI is in constant evolution. I will present some of the technological and instrumental improvements which are planned for the near and mid-term future, and discuss their implications for astrometry in particular. Among them, the PRIMA facility and the proposed GRAVITY instrument are designed to reach the level of 10 microarcseconds in the near-infrared.

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ARAL: a facility to fuel VLTI instruments with photons

Cited by 4 publications

References 5 publications

The PRIMA fringe sensor unit

The PRIMA fringe sensor unit

Methods for multiple-telescope beam imaging and guiding in the near-infrared

The VLT Interferometer

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