Slab and Disk Geometries

Practical limitations arise in the operation of any solid-rod laser owing to the thermal gradients required to dissipate heat from the rod. The thermally loaded cylindrical laser medium exhibits optical distortions that include thermal focusing, stress-induced biaxial focusing, and stress-induced birefringence. These thermally induced effects severely degrade the optical quality of the laser beam and eventually limit the laser output power, either because of an unacceptably poor beam pattern or because of thermal stress-induced breakage of the rod.
The limitations imposed by the rod geometry have long been recognized and a number of designs have emerged, such as slab and disk geometries, in an attempt to reduce the effect of thermal gradients on beam quality.