Stand on the jump pad a total of two times to drop the ceiling above you. Before standing on the pad for the third time, shoot a portal directly above you and the exit portal on the wall up and to the left.
Once you land on the upper floor successfully, look for the angled wall just beside the red laser beam, plant your exit portal on this wall and drop back down to the jump pad.
Stand on the jump pad and you’ll land on a platform right beside the red plunger (that’ll drop a Displacement Cube on the ledge behind you). Now look down and to your left for the next angled wall, place your exit portal here.
Jump through this exit portal and you’ll drop right back onto the jump pad below you, sending you hurtling backwards towards the ledge with the Cube on it.
Place the Cube in the laser beam so it’s hitting the middle of the wall directly to your left (see above).
However, you’re not quite done yet, so fire a portal at either side of the wall and this’ll ensure that the beam reaches the beam receiver. If you’re off target slightly, tweak the placement of your portals until the beam lines up.
A set of stairs will now appear out of the ground behind you, so run up these and into the exit.