So while handheld laser out of the initial phase are the same, but encountered reflective objects (here after the wall, diffuse. The surface of the mirror and smooth with dust), reflecting to a certain point after some photons go, some photons walk less some reflection, so to meet again when they phase is different, so there will be some local bright dark flecks of some places this pattern, known as speckle.
According to the Huygens Finel principle, diffuse surfaces in tiny points of light. Due to the strong coherence of handheld laser, emitted by the point light sources of coherent light beam coherent wavelet. Different phase coherent light beam, the formation of bright spots, dark spots in space, or in bright spots and dark spots between the. The diffuse phase difference between wavelet coherent beam is randomly distributed, and the coherent light beam in space wavelet formed bright spots and dark spots of countless random distribution, known as speckle.
After the presence of speckle often affect the resolution of optical instrument.Handheld laser for holographic lighting, also found that the effect of laser speckle on the holography resolution. It was believed that the speckle is a special noise with useless information, a lot of methods to weaken or even eliminate the speckle. Until 1969, people through research gradually found some useful information carried by the speckle, and gradually developed into a laser speckle measurement techniques.
Diffuse surface handheld laser lighting solid beam spread, and thus the diffuse reflection surface after laser speckle formed in space, in a certain space to determine the location of the observed