Laser heat rays emit continuous beams of light, that must be held on target for long enough to disable it. Typically, the beam will need to dwell on hard targets for several seconds in order to burn through armor. Heat rays cause burning (not tight beam burning) damage.
Heat ray lasers are experimental in early TL 8, and are fielded on warships and as area defense stations against mortars, rockets, artillery, drones, and aircraft in late TL 8. They continue in use into TL 9, until they are superceeded by high energy lasers.