Portal 2 Style Lasers?

I'm trying to make a puzzle game that involves lasers. They would function similarly to the lasers in Portal- there is a laser emitter, then something that it reflects off of, and then a collider that it hits that activates something. The laser emitter and the laser receiver never move.

In terms of how they would work, I would probably use a Raycast and linerenderer, but I don't know how to set these things up. I need to make sure that the laser can't go through walls either.

Could someone explain how I would start something like this?
For a better visual explanation of how I want them to function, look at 1:30 of this video: