Room A1 "Waiting Room"

First of all, make a note of where the receiver to open the exit door is.

Now have a look at what you're able to do from the outset - you can fire the emitter, but can't redirect the particle, for instance.

Can you find a way into the big circular room?

Once you're in, there's only one way back out. It should give you another arrow to play with.

Now you can redirect the particle. Have you had a look at the narrow passage to the left of the door into the circular room?

You should be able to get a particle into the circular room via the slit. You'll note there are some fixed arrows in here. Can you see what they're for?

Try using the fixed arrows to hold a particle in the circular room. This should give you time to think.

Can you reuse any of the arrows to redirect the particle somewhere useful now?

Can you steer the particle out of the circular room, for example?

Make sure you've got a path already set up for it first.

Once the particle is circling the large room, move the left-arrow from in front of the emitter to the top-right of the room, in front of the receiver.

Then use the right-arrow from the circular room to deflect the particle onto the path to the emitter.