After GLaDOS activates the laser, fire a portal where it meets the floor. Walk to the back of the room and stand on the actuated platform beneath the exit. Fire your second portal onto the ceiling above the laser receptacle (an orange glow indicates where to place it). The platform will rise, allowing you to exit the chamber.
Use a couple of portals to acquire the Discouragement Redirection Cube in the rear left side of the room. Pick up the cube, and cross to the other side of the laser. Position the cube such that it directs the beam into the receptacle, making sure that it is on a surface capable of receiving a portal later. Walk up the newly formed stairs to the exit. Fire a portal beneath the cube, and one on the floor next to you, and grab it. Place the cube on the button to continue.
Portal up to the tall platform with the Discouragement Redirection Cube on it. Place a portal above the actuated platform in the middle of the chamber, and take the cube through it. Use the cube to aim the laser at the receptacle, and leave it there. Return to the elevated platform where you found the cube and fire a portal at the spot where the second laser hits the wall. Fire another portal on the floor of the platform, so that it hits the receptacle on the ceiling. Walk through the door!
After entering the chamber, use your portals to direct the laser through the wall to your left, such that it hits the receptacle on the right side of the room. The platform in the back will begin to move - when it reaches the left side, move one of your portals to stop it. Portal over to the platform and press the button to release a cube. Bring the cube onto the moving platform, and use your portals to start it up again. Pick up the cube and carefully use it to block the laser as the platform moves past it. Place the cube on the button.
Use the Aerial Faith Plate to catapult yourself to the other side of the room. Press the button to release a cube which will bounce up and down in the center of the room. Time your next Faith Plate jump so that you can grab the cube in midair as you fly by it. Once you have the cube, place it on the button by the exit, as usual.
The Aerial Faith Plates in this chamber will catapult you across the entire room, but only as long as you place a pair of portals in the two angled platforms on the far right side. You can't see them immediately after entering, so move toward the left until you're able to hit them with portals. Either that, or trust yourself to hit them in midflight.
Once you make it to the other side, press the button and several pieces of garbage will be launched along the same path you took. Play with it if you want (the radio plays a familiar tune...), or ignore it and press the button again to release a cube. Facing the button, you will see a portal-accepting surface on the ceiling to the left. Once you have the cube, fire a portal onto that surface, and another on the floor near you. Drop the box through your portal, and onto the button below.
GLaDOS will mess with you for a bit, but after a couple tries, you'll have a cube to work with. Use it to block the laser, which will lower a platform. Stand on the platform, and raise it again by moving the cube with a couple of portals. When you reach the next level, you'll see two angled platforms. Fire a portal on the platform on the right. You'll need the cube again for this, so fire another portal beneath it to reacquire it.
Now you need to jump through a portal on the floor to launch yourself out of the angled platform and onto the platform which houses the button. Take the cube with you when you do this, and place it on the button to activate an extension on the next platform. Leave the cube there, and repeat the jump, except through the angled platform on the left this time.
GLaDOS will tell you that the Emancipation Grill in this chamber is broken. For an easy achievement, fire a portal into the wall after you walk through the exit door, then return, pick up the cube, and walk through a portal and back into the exit with it.
Once GLaDOS creates some stairs for you, walk up them and through the large Emancipation Grill. Press the button to release a Discouragement Redirection Cube on the other side. It cannot be taken directly through the field, so walk over to it, and fire a portal through the small hole in the glass, and onto the wall on the other side of the field. Fire another portal nearby, and take the cube through it. Use the cube to aim the laser at the switch, then leave it and walk through the exit.