| Popis: |
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 (Ep~4 mj), Δτp ~ 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 (mc1,mc2)—flat mirrors (MO,Me) 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 Me (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. |
