Measurements were made of optical path uniformity, chromium concentration, fluorescence linewidth, large-angle scatter, and laser threshold on 39 flame fusion rubies. Results show that index of refraction variation is explainable by variation of chrome concentration and wander of the optic axis. Residual stress plays little role in optical defects, but may broaden the 77°K linewidth. Optical quality of lasers cut from regions of boules selected by interferometry remains constant after cutting, but warping destroys their parallelism. Threshold increases with chromium concentration, indicating that the rods are optically thick at the pumping bands. Threshold is not correlated with other optical properties, however.
G. W. Dueker, C. M. Kellington, M. Katzmann, and J. G. Atwood, "Optical Properties and Laser Thresholds of Thirty-nine Ruby Laser Crystals," Appl. Opt. 4, 109-118 (1965)