This paper describes a solid state laser concept that scales to MW levels of burst power and MJ of burst energy and burst durations measured in seconds. During lasing action, waste heat is purposely stored in the heat capacity of the active medium. The paper outlines the principal scaling laws of key operational features and arrives at a conceptual design example of the laser head as well as a mobile laser system. © 1998 Cambridge University Press 0263-0346/98 $ 12.50 G.F. Albrecht et al.and average power lasers are designed not to exceed a critical tensile stress value, or the medium will fracture. Depending on how the beam propagates through this medium, the temperature and stress distributions influence the beam propagation, resulting in such phenomena as, for example, thermal focusing and birefringent stress depolarization in rods. Many techniques have been developed to mitigate the imprint of these effects on the beam. In a zigzag slab architecture, special care is taken that such thermo-optical effects are averaged out as the beam propagates through the active medium. The myriad of highly sophisticated and successful commercial systems proves that all these effects have been not only studied extensively, especially in rods and zigzag slabs, but also have been mastered very well indeed. Nevertheless, these average power heat removal effects constitute an intrinsic limit to the steady state average power that the solid state laser can put out. Single shot lasers obviously suffer none of these thermomechanical restrictions, since the medium is in thermal equilibrium with its environment (no heat flow) before the shot, and one simply waits long enough to reestablish this condition before the next shot. The beam thus travels through an active medium essentially free of gradients.The heat capacity laser is conceptually closely related to the single shot laser, in that one rapidly adds single shots at a time scale short compared to thermal diffusion times, 1 that is, short compared to times that begin to establish the thermal gradients of a steady state heat flow condition, and a near adiabatic mounting of the active medium serves to thermally isolate the active medium as much as possible. That means that the waste heat generated during lasing remains, by design, in the active medium, whose temperature now rises each shot by a small amount given by the amount of waste heat generated per unit volume, and the heat capacity of the active medium. Therefore we call it a heat capacity laser. Since the temperature of the active medium cannot rise indefinitely, lasing at some point will have to cease, and the cooling phase begins. During this cooling phase, the temperature of the active medium is again reduced to the starting temperature, and the medium will now be subject to a tensile surface stress, which needs to be managed just like in any other cooled solid state laser.Therefore, an important characteristic of the heat capacity laser is its single shot energy output; it is a rapidly pulsed single shot energy device. ...
