This is something I thought up when I was still planning to use a premade red in my projector. It's to halve the beam with of a red diode laser.
I don't have my regular drawing tools with me but I managed to whip up a quick image of what I mean.
If you have a red with a 8x5 beam, you can make it a 4x5 beam
Edit : you could even use this to decrease divergence in one axis. Expand the axis by 2x and then reduce it back with this setup