The buildup dynamics of a homogeneously broadened continuous-wave Ti: sapphire laser is experimentally investigated for the first time to our knowledge. The average output power of the laser exhibits relaxation oscillation behavior initially and approaches the steady-state value in ≈20 μs. Concurrently, the longitudinal-mode spectrum evolves from a multicluster spectral distribution (tentatively attributed to the spectral windowing effect of the Brewster-angle-cut Ti:sapphire crystal as a birefringent filter) to a single cluster at 787.5 nm. The spectral narrowing (which is due to gain competition in the homogeneously broadened medium), however, takes ≈500 μs. Physical mechanisms that explain qualitatively the two distinctive time scales are presented.