Great explanation FJ, thank you for that!
So whilst digging around I found this article regarding lasers if anyone is interested. It's a rather long read but is interesting, if you're into lasers and knowing about them.....not a dry read ;)
Definitely too much to post without it looking unpalatable and ....well, let's just leave it at that.
qx
http://www.iop.org/cs/page_43644.html