Why does laser light appear granular?

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Offline thedoc

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Why does laser light appear granular?
« on: 21/02/2012 16:03:32 »
Why does laser light appear to be granular when you actually see it propagating through the air?  
Asked by Bob


                                        Visit the webpage for the podcast in which this question is answered.

 

« Last Edit: 21/02/2012 16:03:32 by _system »

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Offline thedoc

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Why does laser light appear granular?
« Reply #1 on: 21/02/2012 16:03:32 »
We answered this question on the show...



Philip -  I think what heís asking about is a phenomenon known as laser speckle which seems to occur on most lasers when they're propagating through space.  If you shine a laser beam onto a wall, you'll see this speckling effect.  Itís a time varying phenomena due to intrinsic noise in the laser beam and itís interfering with itself, and itís a property that's unique to coherent sources of light so it only occurs with lasers.
Chris -   Mike mentioned that lasers shining on skin produce a speckly pattern.  Is that similar?
Philip -   Yes.  The surface of your skin, at a microscopic level, is quite rough.  Light which strikes this surface will reflect and scatter in all sorts of directions.  All surfaces will have a degree of speckle but skin especially so.
« Last Edit: 21/02/2012 16:03:32 by _system »