Single-mode scannable nanosecond Ti:sapphire laser for high-resolution two-photon absorption laser-induced fluorescence (TALIF)

A pulsed Ti:sapphire laser has been developed so as to operate over a wide range of frequencies, even far from the optimum wavelength (790 nm), as a narrow-band light source for TALIF experiments on O, Cl, N and H. The coupling of the optical cavity, both to its injection seeder and to the laser output beam, relies on a reflecting plate, which makes it fundamentally easier to control the coupling coefficient over a wider spectral range than with an ordinary transmission coupler. Two intra-cavity prisms are used to bring the green pumping light longitudinally coincident with the cavity axis, inside the Ti:sapphire crystal. Seeding by a CW Ti:sapphire laser has made it possible to obtain single-mode emission over the whole range of tunability, thanks to the spectral selection of the prisms and to a specifically developed digital/analog controller. Experiments carried out with the system on oxygen atoms inside an oxygen plasma show that the experimental bandwidth is limited essentially by the collisional dephasing rate and the finite pulse duration.