Abstract

The potential of the Ti:sapphire lasers for applications in spectroscopy and differential absorption lidar measurement can be essentially improved when the lasers operate simultaneously at two independently tuned wavelengths.^1-3 Recently, we have demonstrated that for the cw Ti: sapphire laser, a passively self-injection locking technique⁴ is an attractive way to realise this mode of operation. We applied here this technique in novel schemes to obtain efficient two-wavelength operation for a pulsed Ti:Al₂O₃ laser, pumped with a 0.53µm harmonic of Nd:YAG laser (E_p~4 mj), Δτ_p ~ 15 ns). The control is produced by reinjection of a small part (~0.003%) of the cw output back into the non-selective cavity at two wavelengths after the spectral filtering.³ The two-wavelength laser arrangements used are given in Figs, 1a, 1b, and 1c. They have as a principal part a two-outputs Kogelnic-type concave mirrors (m_c1,m_c2)—flat mirrors (M_O,M_e) cavity with a longitudinally pumped 1-cm-long 5×5 mm cross section Ti:Al₂O₃ crystal. The one laser output, this from the flat mirror M_e (R = 70%), is reinjected back at two selected wavelengths λ₁, and λ₂ by the two wavelength retroreflector TWR, based on the Interference wedges (IW, and IW₂);⁵ wedge thickness ~5µm, reflectivity of the coatings R₁ = R₂ = 0.9, and the wedge angle α = 5.10^–5 rad. The wedge transmission at resonant wavelength is ~0.7. In the schemes used, a single interference wedge acts as a tunable spectral filter for one wavelength (which is resonant for the wedge thickness of the incident part) and as a coupler for the second wavelength λ₂, selected by the second wedge IW₂. In the first arrangement (Fig. 1a), which is similar to this applied by us for the cw laser,³ the retroreflection is in coincident beams.

© 1994 IEEE