What is Laser Speckle?
Speckle is a mottled pattern that arises when laser light falls on a non-specular reflecting surface and is caused by interference at the retina of your eye (or at the image plane in a camera) from coherent light reflected by a non-specular (rough, at least on the scale of a wavelength of light) surface. Depending on the laser and surface, the speckle patterns can be quite dramatic. A medium power HeNe laser with a beam expander will demonstrate speckle quite nicely. But it should be present to some extent even with most laser pointers. Note that the effect exists equally strongly whether you are focused on the surface or not. Where the laser spot is large compared to the speckle pattern, the direction and speed of movement of the pattern will be affected by whether you are focused in front (opposite direction, nearsighted) or behind (same direction, farsighted).
Speckle is a mottled pattern that arises when laser light falls on a non-specular reflecting surface and is caused by interference at the retina of your eye (or at the image plane in a camera) from coherent light reflected by a non-specular (rough, at least on the scale of a wavelength of light) surface. Depending on the laser and surface, the speckle patterns can be quite dramatic. A medium power HeNe laser with a beam expander will demonstrate speckle quite nicely. But it should be present to some extent even with most laser pointers. Note that the effect exists equally strongly whether you are focused on the surface or not. Where the laser spot is large compared to the speckle pattern, the direction and speed of movement of the pattern will be affected by whether you are focused in front (opposite direction, nearsighted) or behind (same direction, farsighted). However, if you are far enough away to not resolve structure inside the spot, you get one big speckle which will get brighte
