Moiré deflectometry produces result that appears similar to an
interferometry
Interferometry is a technique which uses the '' interference'' of superimposed waves to extract information. Interferometry typically uses electromagnetic waves and is an important investigative technique in the fields of astronomy, fiber o ...
technique, in which the object to be tested (either phase object or specular surface) is mounted in the course of a
collimated
A collimated beam of light or other electromagnetic radiation has parallel rays, and therefore will spread minimally as it propagates. A perfectly collimated light beam, with no divergence, would not disperse with distance. However, diffraction ...
beam followed by a pair of transmission gratings placed at a distance from each other. The resulting
fringe
Fringe may refer to:
Arts
* Edinburgh Festival Fringe, the world's largest arts festival, known as "the Fringe"
* Adelaide Fringe, the world's second-largest annual arts festival
* Fringe theatre, a name for alternative theatre
* The Fringe, the ...
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
Wind tunnels are large tubes with air blowing through them which are used to replicate the interaction between air and an object flying through the air or moving along the ground. Researchers use wind tunnels to learn more about how an aircraft ...
application for quantitative measurement is moire schlieren, a variation of
schlieren photography
Schlieren photography is a process for photographing fluid flow. Invented by the German physicist August Toepler in 1864 to study supersonic motion, it is widely used in aeronautical engineering to photograph the flow of air around objects. ...
.
In 2012 the first application of the method for the measurement of electron density in
plasma
Plasma or plasm may refer to:
Science
* Plasma (physics), one of the four fundamental states of matter
* Plasma (mineral), a green translucent silica mineral
* Quark–gluon plasma, a state of matter in quantum chromodynamics
Biology
* Blood plas ...
has been published.
The method excels in spatial and temporal resolution comparably with a similar approach of
laser schlieren deflectometry
Laser schlieren deflectometry (LSD) is a method for a high-speed measurement of the gas temperature in microscopic dimensions, in particular for temperature peaks under dynamic conditions at atmospheric pressure. The principle of LSD is derived ...
.
References
Interferometry
{{optics-stub