Light patterns resulting from the Reflection of Coherent Light at rough surfaces.

The term speckle refers to a random granular pattern which can be observed when a highly coherent Light beam from a Laser is diffusely reflected at a surface with a complicated structure, such as a piece of paper, white paint, a display screen, or a metallic surface. This phenomenon results from the Interference of different reflected portions of the incident beam with random relative optical phases. Even minor changes of the conditions, such as of the illuminated spot or the direction of the incident laser beam, can change the detailed shape of a speckle pattern. Speckle patterns can severely degrade the image quality of laser projection displays or disturb position measurements with laser pointers. Speckle can often be avoided by using a Light Source with sufficiently large optical Bandwidth or with an optimized screen.