Applied lasers

The laser has been found useful for short-distance communication or for communication across the macrodimensions of space. Two short-distance voice-communication systems are described¿one requiring careful boresight alignment and the other involving a megaphone-like broad-beam laser that needs little alignment. A laser range-measuring system has been developed that can make distance checks for aircraft refueling or for measuring the altitude of spacecraft landing on the moon. The principles of ranging can also be applied to selective viewing, maintaining a separation of vehicles moving along a set path, or selectively counting certain-sized objects. The laser also can be used in a simple intrusion alarm since its narrow beam can be reflected over a very long distance with little spreading.