For military applications, a laser designator is a device that emits a beam of laser energy which is used to mark a specific place or object, usually for a precision-guided munition such as a guided bomb. U.S. military designators operate at a invisible infrared light wavelength between 1006 and 1054 nanometers, although the signal is modulated or pulsed for security. The functions of designation and of a laser rangefinder may be combined in the same device. Considerable engineering may be needed to meet all the constraints of the battlefield; such a device is far more complex than a simple red laser pointer used by a lecturer, which operates at a much shorter wavelength.
As a start, while the lecturer wants to draw attention to that which is marked with the red dot, there may be very strong reasons that the soldier designating a target does not want the target to know that it is being marked. Even if the soldier is observing and mapping, and not guiding weapons into the target, it still may be important for him to remain clandestine, his presence unknown.
Some targets have optoelectronics that can detect when laser energy is hitting them, even if the beam, in the infrared light spectrum for most military devices, is invisible to the human eye. They may try to jam the sensor looking for the laser designator energy, perhaps by turning on infrared light or firing flares. Modern laser designators do not send a simple continuous wave, or steady set of pulses, at the target, but send a complex, changing, and unique pulse pattern. Assuming a laser-guided weapon is being guided by the designator, the pulse pattern will be known to the sensor in the weapon -- and the weapon will ignore any laser signals that do not match the preset pattern.
While the beams are usually invisible to the human eye, infrared laser energy can damage the eye. A widely ratified international agreement forbids the use of weapons whose "sole combat function or as one of their combat functions, is to cause permanent blindness to unenhanced vision."  The protocol does not apply to blinding as a collateral effect of other laser-based systems, such as weather instrumentation, rangefinders, etc., but it is a widely accepted principle that unless the device is a true laser weapon intended to kill, it is unwise to give even an incidental blinding capability. After all, the beam could accidentally hit onto friendly forces or civilians.
A common U.S. Army system that combines designation and rangefinding, the Lightweight Laser Designator Rangefinder (LLDR), is eye-safe
- Joint Pub 3-09.1: Joint Tactics, Techniques, and Procedures for Laser Designation Operations, 28 May 1999 p. I-5
- , Protocol IV on Blinding Laser Weapons, Convention on Certain Conventional Weapons