Moiré deflectometry produces result that appears similar to an
interferometry
Interferometry is a technique which uses the ''interference (wave propagation), interference'' of Superposition principle, superimposed waves to extract information. Interferometry typically uses electromagnetic waves and is an important inves ...
technique, in which the object to be tested (either phase object or specular surface) is mounted in the course of a
collimated beam followed by a pair of transmission gratings placed at a distance from each other. The resulting
fringe pattern, i.e., the moiré deflectogram, is a map of ray deflections corresponding to the optical properties of the inspected object.
Moiré deflectometry can be a powerful tool for nondestructive optical testing. A major advantage of the technique is that it is less sensitive to mechanical vibration, and it is therefore widely used in the ophthalmic industry for laminar analysis. A similar implementation in
wind tunnel
A wind tunnel is "an apparatus for producing a controlled stream of air for conducting aerodynamic experiments". The experiment is conducted in the test section of the wind tunnel and a complete tunnel configuration includes air ducting to and f ...
application for quantitative measurement is moire schlieren, a variation of
schlieren photography
Schlieren photography is a process for photographing fluid flow. Invented by the Germans, German physicist August Toepler in 1864 to study supersonic motion, it is widely used in aeronautical engineering to photograph the airflow, flow of air ar ...
.
In 2012 the first application of the method for the measurement of electron density in
plasma has been published.
The method excels in spatial and temporal resolution comparably with a similar approach of
laser schlieren deflectometry.
References
Interferometry
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