Continuously tunable diode pumped Tm:YAP laser

Tunable solid-state laser sources emitting in the 2 pm wavelength region are important for applications in atmospheric monitoring and laser radar because many molecular absorption lines are present there. We report on continuously tunable operation of a diode pumped Tm:YAP laser, which is among the most efficient laser materials emitting in the 1.9 - 2 mu m spectral band, while continuous tuning of this material has not yet been reported. The 3 mm long a-cut (Pbnm) crystal sample with 4% at. doping was used. The 400 mu m fiber was used to deliver up to 17 W of pump power to the coupling optics. The differential efficiency in respect to the absorbed pump power reached 57% while the attained optical-to-optical efficiency was 48%. The maximal output of 4.8 W was only limited by the available pump power and relatively low sample absorption. The free running wavelength was measured at 1.99 mu m. A 1.5 mm thick birefringent plate made from quartz inserted under a Brewster's angle was used as a tuning element. The maximal output power of 3.85 W in this set-up was obtained. The laser could be tuned from 1869 nm up to 2036 nm with a maximum at 1985 nm. The tuning range of over 160 nm covers many important atmospheric absorption lines. In this wavelength range, the absorption depth in water changes from 100 mu m (laser wavelength 1.94 mu m) to 400 mu m (wavelength 1.87 mu m) making it potentially attractive for medical applications as a laser scalpel with variable cutting depth.