Is there such thing as a Laser beam detector that returns a non binary result?
What you're looking for sounds more like a laser range finder. 
There are a number of different types of these that works in various ways, depending on your application, some might be better than others.
If you say what exactly you're trying to do it will be easier to help you.

EDIT: Have a look at these, you'll need to figure out what range you want to it work over (I imagine probably about 1m?) and what frequency you need the measurements at (how quickly do you want a note to change?).