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Proceedings Paper

Concept for medium to long range LDA measurements
Author(s): Christian Caspersen
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Paper Abstract

With the realization of optical fibre technology for transmission of high light power new possibilities for configuration of optical systems for LDA measurements are coming up. The increased flexibility of the systems have in the first years of the fibers mainly been used to make the measuring probe smaller. The standard dimension today for these probes is 14 mm. The focal length is around 50 mm. These probes are very well suited for wind tunnel measurements, if the windtunnel is provided with a high quality traversing system, and the blockage of the probe and the traversing system can be accepted. In many situations this is not the case, so there is still a requirement for LDA systems with long focal length, so the optical set-up can be outside the tunnel. Until now this has caused problems due to large required aperture even for one dimensional systems. The size and weight of the system has increased to dimensions impossible to handle and traverse, or they have had insufficient apertures, and therefore suffered from poor signal quality. The problems increase further if two and specially three component systems are generated. The result has been systems, that are difficult to align and to operate, poor resolution and poor signal quality. With the fibre technology many, although not all of these problems can be overcome. This paper will describe new concepts, that although many of them are based upon old ideas, first have come to a mature state now from an engineering point of view. The paper will both describe the theoretical advances by these new concepts, but also some practical examples of realization will be included. The main problem with the long range systems, where several have been built almost from the beginning of LDA technology has been the requirement for the large aperture if a single lens system should be used for both transmission and reception, or the complication in mirror systems for individual transmission beams if individual transmission beams were used. The fibre technology will overcome these problems and add further benefits.

Paper Details

Date Published: 1 November 1990
PDF: 11 pages
Proc. SPIE 1404, ICALEO '89: Optical Methods in Flow and Particle Diagnostics, (1 November 1990);
Show Author Affiliations
Christian Caspersen, Dantec Elecktronik (Denmark)

Published in SPIE Proceedings Vol. 1404:
ICALEO '89: Optical Methods in Flow and Particle Diagnostics
Marshall B. Long, Editor(s)

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