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Optical Slits

Definition: narrow openings through which light can be transmitted

German: Schlitzblenden

Category: general optics

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Optical slits are narrow openings through which light can be transmitted. They are usually made with high precision, often with laser material processing in some resistant metal such stainless steel, molybdenum or tungsten. In some cases, such a slit is made in a thin metallic coating on a glass piece.

Typical slit widths are some tens or a few hundreds of micrometers, but slits with a width of only a few micrometers are also available. The width tolerance can be of the order of 1 μm. The length may be a few millimeters or more.

There are also adjustable mechanical slits, where the slit width can be tuned with a micrometer screw.

Applications of Optical Slits

Optical slits are used in various optical instruments:

  • At the entrance and exit of a monochromator, e.g. of Czerny–Turner type, or an optical spectrograph, there is usually a narrow slit. It prevents the propagation of light on paths which would be possible for light outside the wanted range of transmission wavelengths.
  • Some beam profilers work with a rotating disc with one or more optical slits, where one measures the transmitted optical power as a function of the slit position. Two such discs can be used for obtaining two-dimensional beam profiles.
  • Thin optical slits have been used in interference experiments, for example in the famous double-slit experiment of Thomas Young.


The RP Photonics Buyer's Guide contains 4 suppliers for slits.

See also: optical apertures, pinholes
and other articles in the category general optics


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