Directed-energy weapon

A Directed Energy Weapon (or DEW) is a type of weapon which emits energy in an aimed direction without the means of a projectile. It transfers energy to a target for a desired effect. Some of these weapons are real or in development; others are at present only science fiction.

Lasers
Lasers are standard armament on Covenant warships, and equipped to UNSC Prowlers, used for precision strikes and for point-defense, intercepting fighters and missiles attacking the ship.

Plasma
The Covenant also utilize a type of superheated plasma, contained and guided by a controlled magnetic field, for extremely damaging strikes against UNSC targets, such as warships or glassing a conquered planet. Plasma is also used in the majority of Covenant small-arms, such as the Plasma Pistol, Plasma Rifle, Plasma Grenade and Fuel Rod Cannon.

Particle Beam Weapons
The Covenant also use accelerated particles as weaponry, such as the devastating capitol-ship mounted Energy Projector and the infinitely smaller Type-50 Sniper Rifle System. 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 of yet used it for weaponry. It may be well be that they use it for other uses or with current UNSC fusion power plant technology may need a very big ship (ie Marathon-class cruiser or Super carriers) and the cost of making such a weapon may be so much that the UNSC may feel it would be a waste of time and money to make such weapons. Also for front line usage, it may be too heavy considering the Spartan laser is very heavy with its battery and with current UNSC battery technology, a particle beam cannon may even be heavier then the Spartan laser

As of the early 21st century, humanity had developed particle accelerators, but the machinery needed to work one is massive. At this time, humans also did not understand how particles at such speeds interacted with other matter.