1.   Theodora allowed the beam to travel round the room.

2.   In particular, it turned out to be more difficult than thought to fabricate the long chambers through which the laser beams must travel before reaching the target.

3.   The laser beam travels more slowly through denser air.

4.   The rate at which these rays fall off from the initial blast, the scientists discovered, could be used to calculate the distance the beams have traveled.

5.   In fiber optics, laser beams can travel for miles through fused-silica glass fibers without dissipating or scattering.