From Halopedia, the Halo wiki
The disintegrator is a deleted UNSC weapon in Halo 4, present in the map files. It is very similar to the Spartan Laser, but bulkier in size. As opposed to the standard red laser fired by the Spartan Laser, the disintegrator fires a blue laser instead. In addition, the disintegrator appears to require no time to charge up before firing.