Laser beam fiducial line application for metrological purposes
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aser Beam Fiducial Line Application for Metrological Purposes¶ V. Batusova, J. Budagova, J. Khubuaa, c, C. Lasseurb, M. Lyablina, N. Russakovicha, A. Sissakiana, and N. Topilina a JINR, Joint Institute for Nuclear Research, Dubna, Russia CERN, European Organization for Nuclear Research, Geneva, Switzerland c IHEPI, Institute of High Energy Physics and Informatization, Tbilisi, Georgia Abstract—The possibility for a collimated one-mode laser beam used as a fiducial line is considered. The technology for an “extended” laser beam formation and application for a much-extended fiducial line is proposed. PACS numbers: 42.62.Eh DOI: 10.1134/S1063779609010079 b
INTRODUCTION When metrology measurements have to be achieved, the question of so called “fiducial points” (FP) positioned on the object to be measured and on the measurement stations forming a surrounding or linear network has to be raised. One assumes that the relative locations of these FP’s on objects and stations have been well understood and foreseen so that the correct and comfortable executing of the measurements, networks and objects under study, can be achieved. As a rule the “long-term” FP’s and the measurement stations have a fixed contact with the rock monolith—pillar embedded in soil—that can be equipped with a suitable mechanic tooling for positioning precise, standard measurement units like theodolites, targets, prisms for measuring distances etc and in a very accurate repetitive mode. As the experience shows their relative longterm stability on about a 100 m base is enough to perform measurements for a few years with a relative precision of ~10–6 [1–3]. In some cases it might be useful to foresee some purely mechanical or optical verification devices of the centering structure (clinometers, short leveling from deep rods, etc) in order to verify that no accidental bumps have occurred. In metrology measurements the “fiducial lines” (FL) are often used. They represent a set of FP’s aligned along some line(s). For example the measurement stations are sockets embedded on the tunnel floor and are used to install the LHC elements of which the accuracy is about 1 mm within the main geometrical frame all along the accelerator. The final relative locations of the adjacent machine elements—Qpoles to Qpoles, magnets to magnets—are cross-checked section by section with respect to the smoother line within the best accuracy (a few tenths of a millimeter) by using one unique
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stretched wire attached to the FP’s of the controlled elements [4–7]. High accuracy measures and devices, redundancy whenever possible, cross-checks, errors tracing—specifically when controlling a unique straight section must be considered at all stages of a given process. This is a so-called string metrology when the metrology tasks need to perform the measurements relative to some straight line [8–10]. The used device represents a mechanical set-up where a tensed string connects two FP’s, the real measures being horizontal or planar, radial
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