Submarine

Test Chamber 13: Place portals as shown in the image. Use a portal to move the laser sideways and a time portal to send it into the future. You can take some damage from the laser to travel into the future. Once in the future, rearrange portals so the laser hits the target directly. Head through the door.

Test Chamber 14: Travel to the present via a time portal. Summon a reflector cube and position it in the present as shown. Use a portal to direct a laser through the first node and reflect it into 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, travel back to the future to retrieve the future reflector cube again and bring it to the present. Finally, position the future reflector cube to reflect the laser into the receiver, completing the chamber.

Test Chamber 15: Start by going through the particle field to the left. Place a portal where the laser hits the wall and a time portal on the opposite wall. Travel through the time portal to the future to bypass the particle field. Head 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 so the laser hits 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 be hitting the first receiver, powering an elevating platform. Stand on the platform and shoot a time portal behind the node to raise the platform further, allowing you to summon a reflector cube. Place this cube on the lip above the second receiver. Travel to the future. Pick up the future reflector cube and run into the laser room. Use a time portal to bring the future reflector cube into the present laser room. Position it to reflect the laser into the second receiver through the node. Now, get to the other side of the particle field without going through it (use a portal or time portal). 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 chamber.