Interferometry & Holography
- Interferometry for distance measurements
- Interferometry for optics testing
- TOPTICA’s added value
Interferometry is a well know method to determine distances by splitting a light beam and overlapping the part reflected from a plane at fix distance with the part coming from the object. The interference of the two beams shows maxima and minima with a periodicity of half of the laser wavelength depending on the path difference of the two overlapped beams. This way, any distance variation of the object can be detected by counting interference maxima or minima with a precision down to about 0.1 µm. Similarly, one can also interfere one part of a laser beam coming from a reference plane (e.g. an ideal lens) with a part coming from a test object (e.g. a lens that has to be analyzed). Deviations in the form of the test object from the reference can be seen as intensity differences in the interference picture. Optics testing can also be performed using the advanced method of phase-shifting interferometry which is based on narrow linewidth tunable lasers.
Original holography is a method to record and store an image from an object in such a way that one can later reconstruct the view of the object which appears like a real three-dimensional object. To record such an image, one interferes laser light scattered from the object with part of the laser light from a reference plane. The interference picture can then be recorded on a photo plate. Illuminating the recorded interference photo later with the laser beam reconstructs the light scattered from the object as if it was still be present. The technique can be extended vastly. One can artificially create an interference picture even without having the original object (virtual). After illumination the hologram shows the virtual object in 3-d. Such holograms are widely used, e.g. for bank note security. Holography can also be used to store digital information in 3-d media, hence increasing data storage capacity.
TOPTICA’s added value for interferometry and holography is that we can provide lasers at many different wavelengths and laser with many different coherence lengths from a few µm to more than 100 m. Research grade lasers are also available in the UV (e.g. 248 nm) and special frequency-control modules allow one to sweep the laser frequency in a very precise way.