Collimator

A collimator is a device used to filter a stream of rays (such as X-rays) so that only those travelling parallel to each other in a certain direction are allowed through. The illustration below (top section) shows a leadcollimator used in X-ray machines. The image will be recorded on the plate at the left of the picture. Without a collimator (top picture) rays from all directions will be recorded; for example, a ray that has passed through the top of the specimen but happens to be travelling in a downwards direction may be recorded at the bottom of the plate. This will not produce a readable image. Image:Collimator.jpg In the illustration to the left, (bottom section}, a lead collimator has been added. Effectively, this is a thick sheet of lead with many tiny holes bored through it. Only rays travelling at nearly 90° will pass through - any others will be absorbed by hitting the side of a passage. This ensures that rays are recorded in their proper place on the plate, producing a clear image. Although collimators improve the signal to noise ratio, they also reduce the intensityof the signal--most lead collimators let less than 1% of incident photonsthrough. For this reason, attempts have been made to replace collimators with electronic analysis.

Collimators may be used with laser diodes.

Collimating lenses may also be used in optical systems to make rays of light parallel by (see also Collimating lens).

Proper collimation of a laser source with long enough coherence lengthcan be verified with a shearing interferometer.

Collimators are also used with radiation detectors in nuclear power stationsfor monitoring sources of radioactivity.de:Kollimator nl:Collimator

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It uses material from the http://en.wikipedia.org/wiki/Collimator Wikipedia article Collimator.