These beams can be made to switch on and off in a few billionths of a second. This allows the beams to be coded. The small size and the coded identification of the light spot makes lasers useful as a target marker or designator. Homing missiles or shells and close air support aircraft can be guided by these lasers to engage a target at long ranges. The fast switching action also allows the use of the laser light to measure distances in land surveying equipment and rangefinders.
Lasers make superb range finders.
The laser beam is switched on and off in a few billionths of a second producing a very short pulse. The pulse travels to the target, where some light is reflected back. A timer inside the rangefinder measures how long the pulse took for the round trip. Time is then converted into a distance to the target. The fast switching of the beam on and off allows the pulses to be timed.