Subject: What would happen if you had a tube and shot a laser into it?

I know that seemed vague so here it is:  the tube is in the form of a 
capsule, like the medicine ones, and the entire inside is a seamless 
mirror.  The only seam in it is a tiny hole at the very top wide engough 
only for a small laser beam to fit through, no room to go back out.  The 
laser that you are using is strong enough to burn skin.  Would the capsule 
explode?  This question popped up in my mind at the age of seven, and has 
been bugging me.  Thanks for taking your time to read this.

Re: What would happen if you had a tube and shot a laser into it?