Abstract
The focusing of pumping light by high-index-of-refraction spherical and cylindrical sheaths covering a ruby-rod maser material has been studied both theoretically and experimentally. In the experimental work, the reduction in threshold pumping energy and the increase in optical output energy for the same ruby rod have been measured as a function of the index of refraction of the sheath by using spherical and cylindrical sheaths of water and benzyl benzoate, which have indices of refraction of 1.33 and 1.57, respectively. The results of the measurements clearly show that the spherical sheath is better than the cylindrical sheath. In the theoretical work, a thermodynamical method of analysis has been used to develop an approximate three-dimensional theory for the power absorbed per unit volume at each point in the rod. This theory treats the spherical and cylindrical sheath composite-rod structures in a unified way. The theoretical results are in fair agreement with the experimental ones. Moreover, the theory shows that the spherical sheath of sapphire is an optimum composite-rod optical-maser configuration. In fact, the theory predicts that in this case the threshold pumping energy for maser oscillation should be reduced by a factor of 4, whereas the cylindrical sheath of sapphire should only give an improvement by a factor of 2.4.
© 1963 Optical Society of America
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