There is a large emancipation grill separating the two areas of the room. If you wait a moment, some steps will come out that you can walk up to go past the emancipation grill. Go through, then press the small red button to make a laser redirection cube fall down on the other side of the grill.
Note that whenever you step through the grill, any portals that you created will disappear.
There is a round hole near the small button that you pressed to make a redirection cube appear. Shoot a portal through this round hole onto the wall near the floor. Then shoot a portal somewhere in here.
Go get the laser redirection cube and bring it back into the area with the laser. Jump over it, then use the redirection cube to shoot it into the laser receiver past the emancipation grill.
Go back through the portal that you took the laser redirection cube through, then go into the exit that you opened by shooting the laser into the laser receiver with the redirection cube. Go into the elevator.