Title
Design, analysis and testing of the Optical Tube Assemblies for the ESO VLT Four Laser Guide Star Facility
Author
Henselmans, R.
Nijkerk, M.D.
Lemmen, M.H.J.
Rijnveld, N.
Kamphues, F.G.
Publication year
2012
Abstract
TNO has developed the Optical Tube Assemblies (OTAs) for the ESO VLT Four Laser Guide Star Facility. The OTAs are Galilean 20x beam expanders, expanding a ∅15 mm input beam (25W, 589 nm CW) to a steerable ∅300 mm output beam. TNO has recently successfully completed acceptance testing of the four units, showing compliance to the challenging requirements on output wavefront quality, thermally induced defocus under operational conditions, absolute pointing accuracy and polarization extinction ratio (PER). TNO applied its corrective polishing in combination with the NANOMEFOS measurement machine to produce the ∅380 mm aspherical output lens, resulting in 20 nm rms output wavefront quality. The thermal behaviour of the system has been analyzed by combining optical, lumped mass and FE analyses. A design that is passively athermalized over a large temperature range as well as under the influence of thermal gradients has been developed. Extensive thermal testing has shown a thermally induced defocus of less than 0.15 waves under the operational conditions of 0-15°C and upto -0.7°C/hr gradient. A custom tip-tilt mechanism was designed to steer the output beam over a 4.8 arcmin radius, with less than 0.1" (3σ) accuracy at 1 Hz update rate. The PER was also measured under operational (thermal and tilt) conditions and demonstrated to be well above 99%. This paper describes the design, modelling and analysis, and the test results of these instruments. © 2012 SPIE.
Subject
Athermal design
Beam expander
High-power laser guide star
Optical Tube Assembly
OTA
High Tech Systems & Materials
Industrial Innovation
Mechatronics, Mechanics & Materials
OM - Opto-Mechatronics
TS - Technical Sciences
To reference this document use:
http://resolver.tudelft.nl/uuid:2fa9965d-6606-4e2c-838b-52abbee815d6
TNO identifier
469133
ISBN
9780819491480
ISSN
0277-786X
Source
Adaptive Optics Systems III, 1-6 July 2012, Amsterdam, The Netherlands, 8447 (8447)
Series
Proceedings of SPIE - The International Society for Optical Engineering
Document type
conference paper