Accurate measurement of the room temperature R1 fluorescent line width of forty-two ruby laser crystals has been made using a pressure-scanned Fabry-Perot etalon. In forty-one of these rubies the chromium content was nearly the same, and the R1 line width for all was 5.0 ± 0.3 Å, in agreement with present theories.
Robert A. Benedict, James F. Nester, and Charles M. Kellington, "Measurement of the Room Temperture R1 Line Width of Forty-two Rubies," Appl. Opt. 6, 429-430 (1967)