From Halopedia, the Halo wiki
A directed-energy weapon (DEW) is a type of weapon that uses a non-solid projectile with a high enthalpy (kinetic and thermal energy) rather than solid ballistic ammunition. It transfers energy to a target for a desired effect.
Lasers are used for a wide array of functions, ranging from repair equipment to weaponry. Pulse laser turrets are standard armament on Covenant warships and, unusually, UNSC Prowlers, and are used for precision strikes against small targets, intercepting incoming missiles and fighters, and general point-defense. Other lasers are used to repair equipment by both the Covenant, and the UNSC while the only infantry-portable laser weapon is used by the UNSC, the M6 Grindell/Galilean Nonlinear Rifle or "Spartan Laser". During the Human-Covenant War, the UNSC began using nuclear bomb-pumped X-ray lasers as warheads for anti-ship missiles, such as the M4020 Bident used by Epoch-class heavy carriers. In the post-war era, Hannibal Weapon Systems has experimented with mounting laser weaponry on its testbed XM820B4 Scorpion tanks.
The Covenant's most common weapon type, however, is superheated plasma that is contained within a controlled magnetic field, able to be guided to a target and dealing heavy damage. Ship-mounted plasma weapons can launch torpedoes, capable of tracking their targets with precision, making them devastating in ship-to-ship combat, or can fire very large streams of plasma from afar to "glass" a planet's surface from orbit. Vehicle-mounted plasma weapons usually have a high rate of fire, but lack the guidance systems. Infantry weapons commonly use guided plasma, such as the Plasma Rifle, Plasma Pistol, and the Plasma Grenade. Towards the end of the Human-Covenant War, the UNSC began using nuclear-pumped "focused plasma spears" in ship-to-ship missile warheads.
Particle beam weapons
The Covenant also use accelerated particles as weaponry, such as the devastating capital ship mounted energy projector and the infantry Type-50 particle beam rifle. These weapons use charged or neutral particles, and may appear similar to lasers though the differences are extensive. Though humans have an understanding of accelerated particle technology they have not yet used it for weaponry.
Not much is known about this type of weapon other than it is exclusive to the Forerunners and shares traits from both plasma and particle beam weapons.
Many Promethean weapons are this type and have a tendency to disintegrate targets, and bounce off solid surfaces.
They are either gold-orange or blue in color.
Weaponized hard light seems to be exclusive to the Forerunners as the Covenant never managed to reverse-engineer the technology.