Put a portal on the wall where the laser is shining. Then put a a portal on the wall across from the lower laser receiver on the far wall. This will make the unstationary scaffold move from side to side. Wait for it to reach a point under the white walls on the left side, then move the portal so that it's shining the laser into the upper laser receiver. This disables the laser wall, but it also stops the platform from moving. Use portals to fall onto that platform.
Stand on the end of the platform that is farthest away from the laser wall. Put a portal on the wall to make the platform start moving. When it has gone partway through the laser wall, move the portal to turn off the laser wall. Go to the other end of the platform. Move the portal to make the platform start moving again. Drop down to the lower level when the platform is over the ledge with the small red button.
When the platform moves under the cube chute, press the button to make the cube land on the moving platform. Make the platform stop moving when it's on the far side of the laser wall. Make a portal on the wall above the platform, then make a portal on the wall nearby and go through so that you fall onto the platform.
Use portals to make the platform move to the other side of the laser wall like you did before. Don't jump off of it yet, but make sure that it's close enough to the ledge with the small red button that you can jump down from here.
Put a portal on the wall across from you to make the laser come out of it toward you. Put the redirection cube in its path and turn it so it's shining in laser receiver near the exit door. Once you have confirmed that the laser cube will shine the laser into the exit receiver, leave it on the platform and drop down to where the small red button is. Use portals to go to the side of the chamber with the exit door. Then shine the laser through portals and into the redirection cube. Go through the exit door.
You will notice that there is no elevator down here like usual. Instead, there is a light funnel. Walk into it. Wheatley will give you a very brief tour, then will turn off the funnel, causing you to fall into an office. Go toward the door, which will automatically open. When you reach the end of the walkway, jump down to the walkway below. Follow it to the end, then look down. There is a door down there. Drop down to that door and you will encounter a loading screen.