The possibility to enhance the self-nonlinear emission characteristics in Nd-activated nonlinear crystals by direct pumping into the emitting level <sup>4</sup>F<sub>3/2</sub> is discussed. It is inferred that the reduction of threshold and the increase of the slope efficiency for the intracavity emission at the fundamental frequency caused by the reduction of quantum defect between the pump and the emitted quanta in the case of direct pumping are strongly amplified in the self-nonlinear processes. Moreover, the diminished heat generation could contribute to a more stable emission and to the scaling to a higher power. The possibility to use the direct pumping is determined by the spectroscopic properties of the laser material. This is illustrated for Nd<sup>3+</sup> in Ca<sub>4</sub>GdO(BO<sub>3</sub>)<sub>3</sub>, where, for direct pumping, the thermally activated transition <sup>4</sup>I<sub>9/2</sub>(Z<sub>2</sub>)→<sup>4</sup>F<sub>3/2</sub>(R<sub>1</sub>) at 887 nm is suitable. Pumping in this band induces an enhancement of the self-doubled emission power at 530 nm by ~2.5 times for an absorbed power four to five times above threshold as compared with the 811-nm pumping into the level <sup>4</sup>F<sub>5/2</sub> of Nd<sup>3+</sup>.
© 2004 Optical Society of America
(140.3380) Lasers and laser optics : Laser materials
(140.3580) Lasers and laser optics : Lasers, solid-state
(140.5560) Lasers and laser optics : Pumping
(140.5680) Lasers and laser optics : Rare earth and transition metal solid-state lasers
Voicu Lupei, Gérald Aka, Johan Petit, and Daniel Vivien, "Spectroscopic bases for efficiency enhancement and power scaling of self-frequency multiplication and self-sum-frequency mixing emission in Nd-doped nonlinear crystals," J. Opt. Soc. Am. B 21, 1620-1629 (2004)