We report transient spectral hole-burning studies of the R-2(+/- 1/2) line in 130, 20 ppm and 0.6 ppm ruby between 2.4 and 70 K. The homogeneous line width Gamma(h) is found to be 142 +/- 6 MHz at 2.4 K for both 20 and 130 ppm crystals; this value is in agreement with the T-1 value of 1.1 ns (Gamma(h) = 1/2 pi T-1 = 140 MHz) for the 2 (A) over bar state obtained by Rives and Meltzer who used pulsed, non-selective laser excitation. The line width is dominated by a direct one-phonon relaxation process 2 (A) over bar -> (E) over bar up to 50 K whereas at higher temperatures two-phonon Raman scattering becomes dominant. Cross-relaxation and spin-lattice relaxation times significantly affect pseudo-CW experiments. (c) 2009 Elsevier B.V. All rights reserved.