Abstract

Thulium-ion-based lasers with the emission wavelength near 2 μm have a number of usages from eye-safe laser ranging to medical applications because the output can be tuned to strong water absorption bands existing in 2 μm region. [1] An attractive laser host for thulium is an yttrium aluminium oxide YAlO₃ (ΥAP,ΥAlO) due to its natural birefringence combined with good thermal and mechanical properties similar to those of YAG. [2] In our previous work we have observed instantaneous fluctuations (spiking) of Tm:YAP laser CW output, which can be explained by weak saturable assumption of water vapors inside the resonator and mechanical instability of laser. Such behavior of laser output can be inconvenient in applications like Cr:ZnSe laser pumping. The goal of our work was the comparison of diode pumped Tm:YAP laser with external resonator and with monolithic resonator. In both cases the Tm:YAP crystals with the same parameters were used: doping 4 at. % Tm/Y, length 3 mm, diameter 3 mm, a-cut (Pbnm) of Tm:YAP. The Tm:YAP crystal used in external resonator was provided with antireflection coating centered at 795 nm and 1900 nm. A 30 mm long semi-hemispherical laser resonator was used (output mirror curvature was 150 mm). In case monolithic Tm:YAP laser resonator mirrors were deposited directly on laser crystal. For the generated laser radiation the output coupler reflectivity was 97 % in both cases. For the laser pumping, a fibre coupled laser diode operating at wavelength 0.79 μm was used. The 400 μm fiber was delivering up to 25 W of pump power to the coupling optics. Both lasers were studied under the same pumping and cooling conditions. The obtained results are presented in Fig. 1.

© 2009 IEEE