A laser is a coherent stream of photons.
Laser weapons were available in sizes ranging from personal use to starship mountings. The Megaships of Vavatch Orbital used bow mounted systems to clear obstructions they could not avoid.
Countermeasures included anti-laser chaff and mirror fields. Reflective materials were also effective; the Temple of Light on Marjoin was made of such materials.
The Culture term for a laser weapon was Coherent Radiation Emission Weapons System (CREWS).