To master this stage with three stars, you have to kill all the pigs with just one shot. There are a couple of ways to master this stage. You can either aim to let the bomb explode, or aim your laser at the back of the stage.
Either way you will have to rely on the flying pig killing the two pigs in the front. If it does not work, try a couple more times and you will eventually get it.
Power Activation Point
First Shot Result