Holographic interferometry
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Holographic interferometry is a method of reconstructing to a very high precision the original waveform of light emitted or reflected by an object. This method allows image resolution of nearly the wavelength of the light being used.
To perform holographic interferometry, the most common technique is to allow coherent light (such as laser light) to fall on an object, and the reflected light is then combined with a reference beam of the original light to produce an interference pattern. This pattern may be projected onto a piece of film, or recorded by a CCD (charge-coupled device) and read into a computer. By passing a beam of the same wavelength as the beam used to record the hologram, the image may be re-projected.
Holographic interferometry was first used to study fluid flow around objects of varying profiles (see Tim McIntyre's introduction). After being split by a beam splitter, one half of the laser light is passed through the flow to be studied, and the other half is diverted around the flow chamber. The two beams are then re-combined in the manner described above, producing an interference pattern from which the form of the fluid flow may be reconstructed.
The most common method of reading such a hologram is to, using a computer, perform a Fourier transform on the interference pattern, allowing a highly accurate approximation of the original form of the object or flow under study.
