Naked Science Forum

Non Life Sciences => Physics, Astronomy & Cosmology => Topic started by: thedoc on 21/02/2012 16:03:32

Title: Why does laser light appear granular?
Post by: thedoc 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. (http://www.thenakedscientists.com/HTML/podcasts/show/20120219/)

 

Title: Why does laser light appear granular?
Post by: thedoc on 21/02/2012 16:03:32

We answered this question on the show...



Philip -  I think what he’s 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.  It’s a time varying phenomena due to intrinsic noise in the laser beam and it’s interfering with itself, and it’s 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.