28 June 2013 4DAD: a device to align angularly and laterally a high-power laser using a conventional sighting telescope as metrology
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Abstract
The 4DAD, Four Dimensions Alignment Device was developed in the frame of the project 4LGSF (4 Laser Guide Star Facility) for the AOF (Adaptive Optics Facility) on the ESO VLT (Very Large Telescope). It is used to accurately align with respect to kinematic interfaces and mirror alignment targets, a 20 W-class laser source in lateral and angular directions. 4DAD is of size 25x25x15cm and is based on a commercial CCD beam profiler. The incoming beam is highly attenuated at 589 nm and split in two parts through a set of beam conditioning optics. One beam is directed onto the detector revealing lateral movements whereas the other part is refocused to reflect angular changes in the incoming beam. Both lateral and angular beam positions are simultaneously recorded as pixel coordinates on the single CCD. The distinctive feature of 4DAD is its metrology, i.e. the pixel reference coordinates are recorded through the cross projection from a conventional sighting telescope. The device is capable of being used with a low-power white light sighting telescope (alignment reference) as well as with a high power laser beam (to be aligned) without any optical configuration change. Mounted on a reference frame, it can align all 4LGSF laser units beams, giving them equal optical interface and interchangeability. The sighting telescope is the main alignment equipment for the 4LGSF, thus all sub-systems, including 4DAD are aligned, merged, using a simple, single, practical and well-known alignment instrument. The alignment strategy, the design, and results of 4DAD are presented.
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Christophe Dupuy, Thomas Pfrommer, Domenico Bonaccini Calia, "4DAD: a device to align angularly and laterally a high-power laser using a conventional sighting telescope as metrology", Proc. SPIE 8450, Modern Technologies in Space- and Ground-based Telescopes and Instrumentation II, 845059 (28 June 2013); doi: 10.1117/12.925213; https://doi.org/10.1117/12.925213
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