Enhancement of Spectral Purity of Injection-Seeded Titanium:Sapphire Laser by Cavity Locking and Stimulated Brillouin Scattering

We report improvements to and better characterization of the spectral purity of a diode laser injection-seeded, cavity-locked titanium:sapphire laser that serves as the source for a previously reported rubidium vapor spectrally filtered Thomson scattering apparatus at 780.24 nm. In a detailed set of measurements the spectral purity P of the laser, defined as the ratio of the narrowband component of the laser output to the total output, has been studied as a function of frequency mismatch between the seed laser frequency and the central frequency of the unseeded cavity. It is found that spectral purity exceeding 0.999 can be obtained for a seed-cavity mismatch as high as +-0.25 nm, corresponding to approximately 950 cavity longitudinal-mode spacings and as high as ~0.9999 for a cavity-seed mismatch in the range +0.10 nm (380 mode spacings). It is also shown that the addition of an external-cavity stimulated Brillouin-scattering phase-conjugate mirror increases both the spectral purity, to a minimum of 0.99999, and the cavity-seed mismatch range, to +-0.25 nm, for which this maximum effective purity is obtained.