BOOK_CONTENT
From Optical Shop Testing

The size (spatial coherence) and monochromaticity (temporal coherence) of the light
source must satisfy certain minimum requirements that depend on the geometry of
the system, as described by Hansen (1955, 1984) and by Birch (1979). It is interesting
to know that if the optical element under test has very steep reflections, the state of
polarization of the light may change in the reflection, introducing changes in the
contrast (Ferguson, 1982). However, in most of the cases, the important factor in the
contrast is the coherence of the light source.

2.3.1.   Spatial Coherence

The light source for interferometry must satisfy some minimum requirements of
spatial as well as temporal coherence, depending on the interferometer configuration
and the specific application and needs. As described in Chapter 1, Section 1.1.2.,
some gas or vapor lamps can be used in conjunction with a small pinhole to
illuminate an interferometer. These lamps with the pinhole do not have perfect
spatial and temporal coherence. A gas laser, however, has perfect spatial coherence
and can have almost perfect temporal coherence. We might think at first that this is
the ideal light source for interferometry, but this is not always the case. The
coherence length is, in...


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Optical Prisms
Optical prisms are blocks of optical material with flat, polished sides that are arranged at precisely controlled angles to one another. They are used in optical systems to deflect or redirect beams of light. They can invert or rotate images, disperse light into component wavelengths, and separate states of polarization.
Optical Lenses
Optical lenses are transparent components made from optical-quality materials and curved to converge or diverge transmitted rays from an object. These rays then form a real or virtual image of the object.  This area includes micro lenses.
Cylindrical Lenses
Cylindrical lens have at least one surface that is formed in the shape of a cylinder. Cylindrical lenses are used to correct astigmatism in the eye, and, in rangefinders, to produce astigmatism, stretching a point of light into a line.  This area includes micro cylindrical lenses as well.
Gradient Index Lenses
Gradient index (GRIN) lenses focus light through a precisely controlled radial variation of the lens material's index of refraction from the optical axis to the edge of the lens.
Fresnel Lenses
Fresnel lenses resemble a planoconvex or planoconcave lens that is cut into narrow rings and flattened. If the steps are narrow, the surface of each step is generally made conical and not spherical.

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