Introduction to speckle

Outline


Fully developed speckle (computer simulation)


Definition of speckle contrast

This page briefly introduces basic understandings of speckle phenomena. List items followed are relevant to speckle research on how it is generated, measured and reduced.


Speckle contrast measurement system

When the coherent light is scattered on the random rough surface, speckle is inevitably generated as its interference on the observer’s retina. Speckle contrast is defined as the ratio of the standard deviation to the average intensity over the speckle pattern. When the contrast is unity, it is called fully developed speckle, which is the original form of speckle.

Speckle standard diffuser is devised to generate stable and fully developed speckle. To measure precise contrast, it is essential to eliminate influence of the specular reflection on the standard diffuser and the back reflection of its transmitted light. For these purpose, the conic frusta are used for field of view restriction on the camera and beam dumping behind the screen.

Speckle contrast can be measured on the CCD camera by applying a proper size of pin hole in front of the camera objective lens. A cooled CCD camera is preferable for the contrast measurement to reduce dark current component among the readout noise.

Finally, very efficient speckle reduction device using Helmholtz tuning forks driven vibrating diffuser is demonstrated.

Oxide Corporation

Speckle contrast Measurement System