A new technique has been applied in experimental work on ruby optical masers with dramatic results. The techniques involved elastically deforming the medium and thereby invoking the stress-optic effect. Strikingly, it permitted optimizing the elastic deformation of any particular ruby specimen to reduce significantly its pumping-energy requirements for the onset of maser oscillations. At the same time, the divergence of the emergent beam could be reduced by a sizable fraction to that characteristic of low-order radiation modes.
Morley S. Lipsett and M. W. P. Strandberg, "Mode Control in Ruby Optical Masers by Means of Elastic Deformation," Appl. Opt. 1, 343-357 (1962)