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A few general comments should be made concerning these presentations in order to develop some degree of consistency so that we can arrive at some comparative evaluation of their results. First, each author was asked to describe as accurately as possible the experimental conditions under which his damage experiments were performed. The first thing that comes to mind is the author's definition of what he calls damage. Is it the first occurrence of a physical or material failure, that is, the rod falling apart, or is it some measure of the degradation in the output characteristics? It is very important that we get this kind of definition from each author. Second, some people prefer to do experiments in focused beams, while others prefer to use unfocused or slightly divergent beams. The authors were asked to address the question of doing experiments in focusing geometries where phenomena such as self-focusing or blooming may occur within the material thus making it very difficult to ascertain exactly what the power density is at the onset of damage. Finally, they were asked to define as completely as possible the characteristics of the incident laser beam that was used in the damage studies such as its power, intensity distribution, beam divergence, or spatial beam quality in general. They should also comment on the optics associated with the experiment, and carefully describe the time history of the pulse. Furthermore, they should be careful in describing the state of the glass sample at the time of damage assessment, for example, whether it is pumped or unpumped, external to or inside the cavity, or, if it is active, the level of inversion. Although the glass manufacturers themselves normally give us a good characterization of the material on which their damage studies have been performed, we should appreciate it if other people would also characterize the glass or material that they have used for these damage assessments.
Guenther, Arthur H.