Here are the 2 texture files and how I changed them...
cutting_beam
cutting_beam2
Here are a couple of ingame screenshots of them in action...
cuppled with the right sound file, it works great.
but you can see how there are multiple instances of the beam in each texture file... 6 of them... so all you need to do is to narrow each instance... you just need to play with the files abit until you like what you see.