The LBT (Large Binocular Telescope), located at about 3200m on Mount Graham (Tucson, Arizona) is an innovative project undertaken by institutions from Europe and USA. LINC-NIRVANA is an instrument which provides MCAO (Multi-Conjugate Adaptive Optics) and interferometry, combining the light from the two 8.4m telescopes coherently. This configuration offers 23m-baseline optical resolution and the sensitivity of a 12m mirror, with a 2 arc-minute diffraction limited field of view. The integration, alignment and testing of such a big instrument requires a well-organized choreography and AIV planning which has been developed in a hierarchical way. The instrument is divided in largely independent systems, and all of them consist of various subsystems. Every subsystem integration ends with a verification test and an acceptance procedure. When a certain number of systems are finished and accepted, the instrument AIV phase starts. This hierarchical approach allows testing at early stages with simple setups. The philosophy is to have internally aligned subsystems to be integrated in the instrument optical path, and extrapolate to finally align the instrument to the Gregorian bent foci of the telescope. The alignment plan was successfully executed in Heidelberg at MPIA facilities, and now the instrument is being re-integrated at the LBT over a series of 11 campaigns along the year 2016. After its commissioning, the instrument will offer MCAO sensing with the LBT telescope. The interferometric mode will be implemented in a future update of the instrument. This paper focuses on the alignment done in the clean room at the LBT facilities for the collimator, camera, and High-layer Wavefront Sensor (HWS) during March and April 2016. It also summarizes the previous work done in preparation for shipping and arrival of the instrument to the telescope. Results are presented for every step, and a final section outlines the future work to be done in next runs until its final commissioning.
GRAVITY is a second generation near-infrared VLTI instrument that will combine the light of the four unit or four auxiliary telescopes of the ESO Paranal observatory in Chile. The major science goals are the observation of objects in close orbit around, or spiraling into the black hole in the Galactic center with unrivaled sensitivity and angular resolution as well as studies of young stellar objects and evolved stars. In order to cancel out the effect of atmospheric turbulence and to be able to see beyond dusty layers, it needs infrared wave-front sensors when operating with the unit telescopes. Therefore GRAVITY consists of the Beam Combiner Instrument (BCI) located in the VLTI laboratory and a wave-front sensor in each unit telescope Coudé room, thus aptly named Coudé Infrared Adaptive Optics (CIAO). This paper describes the CIAO design, assembly, integration and verification at the Paranal observatory.
The LBT (Large Binocular Telescope) located in Mount Graham near Tucson/Arizona at an altitude of about
3200m, is an innovative project being undertaken by institutions from Europe and USA. The structure of the
telescope incorporates two 8.4-meter telescopes on a 14.4 center-to-center common mount. This configuration
provides the equivalent collecting area of a 12m single-dish telescope.
LINC-NIRVANA is an instrument to combine the light from both LBT primary mirrors in an imaging Fizeau
interferometer. Many requirements must be fulfilled in order to get a good interferometric combination of the
beams, being among the most important plane wavefronts, parallel input beams, homotheticity and zero optical path
difference (OPD) required for interferometry. The philosophy is to have an internally aligned instrument first, and
then align the telescope to match the instrument.
The sum of different subsystems leads to a quite ambitious system, which requires a well-defined strategy for
alignment and testing. In this paper I introduce and describe the followed strategy, as well as the different solutions,
procedures and tools used during integration. Results are presented at every step.
LINC-NIRVANA is an instrument combining the two 8.4 m telescopes of the Large Binocular Telescope (LBT)
coherently, in order to achieve the optical resolution of the 23 meter baseline. For this interferometric instrument
concept, the common beam combination requires diffraction limited optical performance. The optics, realized as a
Cassegrain telescope design, consists of aluminum mirrors, designed and manufactured to fulfill the challenging
specifications required for interferometric imaging. Due to the science wavelength range from 1 μm to 2.4 μm, covering
the J, H and K band of the atmosphere, the complete beam combiner including the optics is operated in cryogenic
environment at 60 Kelvin. Here, we demonstrate the verification of the optical performance at this temperature for
classical in-coherent and coherent illumination. We outline the test setup and present the achieved results of wavefront
error for the individual beams and fringe contrast for the interferometric point spread function.
This paper continues the already presented integration of the interferometric camera with the focus on the performance
of the cryogenic optics.