Spectroscopic and 3 Micron Lasing Properties of HOLMIUM:YTTRIUM(3)ALUMINUM(5)OXYGEN(12) Incorporating NIOBIUM(3+) Deactivator and YTTERBIUM(3+) Sensitizer Ions.

A 3 μm holmium laser incorporating neodymium as a deactivator of the long-lived Ho ^{3+} ^5I _7<=vel was demonstrated for the first time. Laser action was observed near 3 μm on multiple transitions between the Stark manifolds of the excited Ho^{3+} ^5I_6 and ^5I_7<=vels. The yttrium aluminum garnet (YAG) crystal contained 10% atomic Ho^{3+} and 1% Nd^{3+}. In addition to (Ho, Nd):YAG, crystals of 15% Ho:YAG and (10% Ho, 10% Yb):YAG were studied. Detailed measurements of the fluorescence lifetimes of the levels involved in laser transitions demonstrated the existence of strong ion-ion interactions in the crystals. By following the fluorescence for many e-folding times, distinct non-exponential behavior was observed. Such behavior has not been reported previously for Ho:YAG. Dramatic reductions in the lifetimes of the Ho^{3+} ^5I_7 and Nd^{3+} ^4 F_{3/2}<=vels were observed in the (Ho, Nd):YAG crystal. Lasing was observed at 2.940 and 3.011 μm from Ho^{3+} ions and simultaneously at 1.064 mu m from the Nd^{3+} ions (all values are +/-0.003 μm) in (Ho, Nd):YAG. Substitution of the output mirror to one having nearly equal reflectivities at 1.06 and 1.34 μm resulted in lasing from Nd^{3+} at both 1.064 and 1.339 μm during individual flashlamp-pumped pulses, contrary to normal Nd:YAG laser operation. The 15% Ho:YAG produced laser emission at 2.941 and 3.011 mum, while (10% Ho, 10% Yb):YAG lased as 2.942, 2.944, 2.947, and 3.013 mum. Laser emission at 2.940 μm was previously reported in Ho-doped YAG, but the additional long-wavelength lines are reported for the first time. The observation of multiple 3 μm laser lines in (Ho, Yb):YAG permitted tentative identification of the Stark levels involved in lasing. The 3 μm laser performance of each of the laser crystals was measured using flashlamp pulses of 50 to 300 mus duration. Both (Ho, Nd):YAG and (Ho, Yb):YAG produced larger output energies at higher efficiencies than the 15% Ho:YAG crystal. (Ho, Yb):YAG provided up to 41 mJ/pulse with thresholds as low as 5.5 J and repetition rates up to 39 Hz. The improved 3 μm laser performance observed with the addition of sensitizer and deactivator ions to holmium-doped YAG crystals suggests that efficient, high repetition rate 3 μm holmium lasers might be engineered. (Copies available exclusively from Micrographics Department, Doheny Library, USC, Los Angeles, CA 90089-0182.).