If you it's overpowered or at least up to spec, and you focus it to the tinyest spot and the balloon is just right and absorbs the light really well, yes.
Or if you do like this guy http://youtube.com/watch?v=4NNPtnTYdsY
But seriosly, it's possible to pop a balloon with a 5mW.Daedal had a video of him doing it with a WL CORE that he tested at about 4.9mW Needless to say he was using a lens and a very black balloon :.