Disk Amplifiers

Solid-state glass-disk amplifiers were considered very early in the development of high-brightness pulsed laser systems in order to solve problems of cooling, aperture size, gain uniformity, and pumping efficiency. In a disk laser amplifier pump radiation is distributed uniformly over the faces of the slab.
Pump-induced slab heating is uniform laterally, thus allowing transverse temperature gradients to be minimized. Such temperature gradients give rise to distortion in the slab just as in the rod geometry. In contrast to the rod geometry, however, the transverse gradients in the slab geometry arise only from spurious effects in pumping and cooling, whereas in the rod geometry, transverse temperature gradients arise from the principal cooling mechanism.
The Brewster angle disk lasers have been primarily developed for very high peak-power and relatively low average-power operation, with the slabs and coolant all approaching thermal equilibrium in the interval between pulses. To operate the Brewster angle slab laser at high average power requires adequate cooling as, for example, with forced convection over the faces. In addition, since the laser beam must pass through the coolant, the problem of thermal distortion in the coolant must be dealt with. This operating mode requires that the slabs be sufficiently thin so that the cooling time is several times less than the laser repetition period. Figure 1 shows a configuration of a gas-cooled disk module which could potentially be developed for high average power operation, particularly if the Nd : glass slabs are replaced with crystalline laser host materials.

FIGURE 1. Concept of a gas-cooled disk amplifier module designed for high average power operation.