Portals

Test Chamber 13: Place portals as shown to redirect the laser. Use a time portal to move the laser into the future. Enter the future by passing through the time portal. Rearrange portals in the future to direct the laser into the target, then exit the chamber.

Test Chamber 14: Travel to the present via a time portal. Summon a reflector cube and position it in the present as indicated. Use a portal to direct a laser through the first node, then use the reflector cube to guide it through the next two nodes. Travel to the future. Use portals to bring a laser into the present through the time portal, ensuring it passes through the node. Retrieve the reflector cube from the future and bring it to the present via a time portal. Adjust the present reflector cube to hit all three nodes. If necessary, return to the future to retrieve the future reflector cube again. Position the future reflector cube to reflect the laser into the receiver, completing the chamber.

Test Chamber 15: Enter the chamber and pass through the particle field to the left. Place a portal on the wall where the laser hits and a time portal on the opposite wall. Travel through the time portal to the future to bypass the particle field. Proceed to the other side of the room and use another time portal to return to the present, now on the other side of the particle field. Place a new portal on the upper wall above the laser room to direct the laser to the first receiver. Travel to the future and place a portal on the small wall in the laser room to aim at the receiver. Return to the present. The laser should now power an elevating platform. Stand on the platform and place a time portal behind the node to raise it further, allowing you to summon a reflector cube. Place this reflector cube on the lip above the second receiver. Travel to the future. Retrieve the future reflector cube and bring it back to the present via a time portal into the laser room. Position it to reflect the laser into the second receiver through the node. To reach the other side of the particle field without passing through it, use an existing portal or a time portal. Once in the present on the other side, climb the stairs and use a portal on the upper wall to hit the third receiver. Finally, move the reflector cube onto the switch to complete the test chamber.