Please explain the cause of the laser speckle pattern

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In summary, the laser speckle pattern is caused by the interference of light waves that are scattered by a rough surface. This scattering results in a random and ever-changing pattern of bright and dark spots, known as speckles. The size and intensity of these speckles can provide information about the surface properties of the object being illuminated, making the laser speckle pattern a useful tool in various fields such as imaging, remote sensing, and surface analysis.
  • #1
SF
I was playing with a laser pointer and a concave mirror and I managed to get a 5mm beam to spread over a 30cm area.
http://img361.imageshack.us/img361/1884/mspaintfg0.png
http://img228.imageshack.us/img228/1866/lpuc9.jpg
http://img228.imageshack.us/img228/3581/lp0ii9.jpg

The irregular pattern remained stationary even when I moved the beam, so I guess it's due to (a) irregularities in the mirror or (b) impurities in the laser's lens?
 
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  • #2
I expect you are talking about a speckle pattern... Look up laser speckle in Wikipedia...
 
  • #3


The cause of the laser speckle pattern is due to the interference of light waves. When a laser beam hits a surface, it reflects off of the surface in a predictable manner. However, when the surface is not completely smooth or there are impurities present, the reflected light waves interfere with each other, creating the speckle pattern that you observed.

In the case of the concave mirror, the irregularities in the surface of the mirror cause the reflected light waves to interfere with each other, resulting in the speckle pattern. This is because the light waves are bouncing off of different parts of the mirror surface, creating different interference patterns.

Additionally, impurities in the lens of the laser can also contribute to the speckle pattern. These impurities can cause slight changes in the direction of the laser beam, resulting in different interference patterns when the light is reflected off of the mirror.

In summary, the laser speckle pattern is caused by the interference of light waves due to irregularities in the surface of the mirror or impurities in the laser's lens. This phenomenon is common in laser systems and is often used in applications such as holography and laser imaging.
 

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