Why does laser light appear to be granular when you actually see it propagating through the air?
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.