Laser

Description

In video games, lasers are often seen as weapons.  In reality, a laser, better scientifically described as a 'directed-energy weapon', capable of significant, physical damage, has yet to be used in combat.  Lasers have, however, been used as targeting devices to guide other weapons, such as missiles, to their targets; Sights to help aiming with guns and fences to discourage to pass through somewhere by various methods
The word Laser itself, comes from the acronym Light Amplification (by) Stimulated Emission (of) Radiation. 

Laser weapons        

What may be the first example of a weaponized laser in science fiction is H.G. Wells', War of the Worlds; published in 1898.  In War of the Worlds, alien ships fire invisible "heat-rays".
In video games, lasers are often portrayed as having a direct, point A to B, trajectory.  The laser is sometimes a sustained beam, like Star Trek's phaser, intermittent with slow moving bolts, like the Star Wars laser, intermittent with hitscan beams like the Renegade lasers, sustained with a wide beam like in Gundam or having ricocheting beams like the Blood II's Death Ray. 
 

Laser weapons are energy weapons who exists in various shapes and forms they can be small weapons up to large and huge weapons, there is light sabers, beam scythes, beam tridents, beam naginatas, laser pistols, blasters, laser rifles, laser sniper rifles, laser shotguns and laser cannons,
these weapons have often specific proprieties in therms of damage. Laser guns are often automatic except when they are very powerful and needs a recharge time.
Lasers can have damage bonus against certain enemy types, burning effects or a strong cutting power like if the laser beam is a sort of powered saw and such things,
laser beams are often visible and uses often the primary colors like blue, red or green when games tends to have a little of realism, but there is sometimes purple and yellow lasers.
 

Laser guidance systems

These lasers are often used for guiding missiles, some other projectiles can be guided with but most of the times only missiles can be guided in a such way, the hit probability of a such weapon is dependent of the player ability to maintain its target in sight, when the missiles can be destroyed by enemies, the player should aim elsewhere until the missile is nearby the target to finally aim it. 

Laser Fences

Laser fences are often highly visible, they can impede the player to go through, by acting like a solid fence, causing damage if we go through, or being laser triggers to activate dangerous traps, security systems and alarms.  

When they acts like a damaging fence it's sometimes so damaging that the player instantly die, when they activate traps the can be explosives like the Duke Nukem laser trip bomb, or some other things like a trapped floor or ceiling and many things. when it comes to security systems, they can release dogs, pop up turrets, drones and other things. 

Some fences have moving laser beams, it happen that a player should use his acrobatic skills to avoid them, to avoid any penalty.  

Laser Sights

Laser sights are used to improve accuracy, mostly when there is no indicator or an approximate indicator to where we aim, most games uses crosshairs, but it happen that the projectile doesn't go every time at its center, it often happen in games with expandable crosshairs or because the crosshair doesn't indicate exactly its center.