When a target is marked by a designator, the beam is invisible to the eye. Instead, a series of coded pulses of laser-light are fired. These signals bounce off the target, where they are detected by the seeker on the laser guided munition, which steers itself towards the centre of the reflected signal. Unless the people being targeted possess laser detection equipment or can hear aircraft overhead, it is extremely difficult for them to tell whether they are being marked or not. Laser designators work best in clear atmospheric conditions. Cloud cover, rain or smoke can make reliable designation of targets difficult or even impossible
Laser designators may be mounted on aircraft, ground vehicles, or handheld. They are usually accompanied by a lower pulsed output, sometimes a separate laser, used for rangefinding. Rangefinders are often 1.57 um or thereabouts, they usually emit just one pulse. That pulse is used to measure the distance to some target or object of interest.
The Lockheed Martin Sniper Pod is an example of an airborne unit. It now equips multiple USAF platforms such as the F-16, F-15E, B-1, B-52, and A-10C. It also operates on multiple international fighter platforms. The U.S. Navy currently employ the Litening II Targeting Pod and the Raytheon ATFLIR on a variety of strike aircraft. The Litening II is used by many other of the world’s air forces.
U.S. Air Force and Marine Corps typically employ a lightweight device, such as the AN/PED-1 Lightweight Laser Designator Rangefinder (LLDR), permitting them to designate targets for Close Air Support aircraft flying overhead and in close proximity to friendly forces. Northrop Grumman's LLDR, using an eye-safe laser wavelength, recognizes targets, finds the range to a target, and fixes target locations for laser-guided, GPS-guided, and conventional munitions. This lightweight, interoperable system uniquely provides range finding and targeting information to other digital battlefield systems, allowing the system to provide targeting information for non-guided munitions, or when laser designation is unreliable due to battlefield conditions.
Handheld units have long been used for soldiers to take with them on a march, or to have with them as they parachute into the front lines, etc. These handheld units are usually characterized by less output energy, many ancillary services such as GPS, Azimuth, and much more, as well as being very lightweight, and more electrically efficient than other laser designators.
Laser Markers: A laser marker is usually just a laser designator with much lower energy. Many of these are ~25 mJ at 1064 nm.
Laser illuminators: A device for enhancing the illumination in a zone of action by irradiating with a laser beam. (Dictionary of Military and Associated Terms. US Department of Defense 2005.) Generally the illuminators used in the military are lasers that emit wavelengths which human eyes cannot see but which can be detected with various tools found in the military such as Night Vision Goggles.