1.06-µm Cr, Nd:Gd3Sc2Ga3O12 laser pumped by 1-W visible laser diodes

The 1.06-µm Nd transition in co-doped Cr, Nd:Gd3Sc2Ga3O12 (Cr,Nd:GSGG) is shown to produce efficient, low threshold laser operation when pumped with visible laser diodes at 670 nm. Population of the upper laser level occurs by rapid and efficient energy transfer from the Cr3+ 4T2 state to the Nd 4F3/2 state. Since the Cr3+ absorption is quite broad, laser efficiency is insensitive to pump wavelength over the range of wavelengths accessible to the AlGaInP laser diodes. Consequently thermal control of the diode wavelength is unnecessary. Laser threshold powers were measured to be wavelength independent over the range of 610–680 nm when pumped with a dye laser. Diode pump power levels as high as 300 mW cw and 1 W long-pulse were used. Two Cr3+ ion densities were used: 1 × 1020 cm-3 and 2 × 1020 cm-3. The higher doped rod provided the best results. The lowest threshold power measured was 0.94 mW and the highest output powers obtained were 43 mW cw and 173 mW pulsed. The best slope efficiency obtained was 42.2%. This is 78% of the slope efficiency calculated by multiplying the quantum defect by the measured Cr-to-Nd excitation transfer efficiency. Measured losses were 0.4% cm-1.</jats:p

Cr-doped lasers for diode pumping

Results on the pumping of several tunable, Cr-doped solid-state lasers at 670 nm are presented in detail. An alexandrite laser was diode pumped in a low-threshold resonator, providing a slope efficiency of 25% and requiring only 12 mW to exceed threshold. The spectral bandwidth was 2.1 nm, and temporal output spiking diminished as the pump power increased. Cr:LICAF was pumped at 670 nm with a dye laser. A threshold power of 56 mW and a slope efficiency of 37% were obtained. Both cw and repetitive Q-switched operation of this laser were demonstrated for the first time. The LICAF laser produced over 170 mW cw and 26 µJ at 3 kHz. The temporal output of the LICAF laser showed large amplitude fluctuations, even for high pump power. A Findlay–Clay analysis was performed for both lasers to obtain the singlepass loss and small-signal gain.</jats:p