A heavy laser is a laser weapon about the size of a Machine Gun. It must be mounted on a tripod or a swivel mount to be fired. It has longer range than a laser rifle, and a minimum SEU setting of 5. Otherwise it operates the same as the laser rifle.
Heavy Laser, Vehicle-mounted EditA vehicle mounted heavy laser is even more powerful than a standard heavy laser. As the name implies, it is typically mounted on a vehicle, though nothing prevents it from being mounted in a fixed fortification as well. It is capable of being dialed up to 30 SEU per shot, and has a longer range. Vehicle-mounted heavy lasers operate off of a power econopack.
The standard heavy laser is described in the Alpha Dawn rulebook. The vehicle-mounted version of from the article "Tanks a Lot" in Dragon #91.