I did some tests. The lasers I ordered are for cutting or engraving. This means that their focal point is relativety narrow. I have to focus them, so set of points that will pop the balloon is a line about 15 cm long in front of the quadcopter. That should be good enough for now. I also have two relays that will be in series with the laser: one will be controlled from a manual wireless transmitter, and one will be controlled from the quad. This is for safety.