Abstract
Nd3+ doped optical fibers are interesting medium for both laser emission and amplification in the near infrared. The stimulated transitions start from the 4F3/2 level. However higher energy levels above 4F3/2 can absorb and perturb the emissions. This process is especially probable in glasses whose the disordered structure is responsible for the inhomogeneous broadening of the transitions. Therefore it's very interesting to know the effect of these excited state absorptions (ESA) on the stimulated emissions (SE). The experiment are done on Nd3+ ions in bulk ZBLAN (Zr-Ba-La-Al-Na) and BIG (Ba-In-Ga) fluoride glasses[l]. We use a pump probe technique to measure directly the ESA and SE cross sections from the 4F3/2 level. A Ti:sapphire laser pumps the 4F3/2 level and a white lamp probes the transmission from 0.82 to 1.44 µm. The spectrum is calibrated to the ground state absorption cross section of the transition 4I9/2 → 4F3/2 For the 4F3/2 → 4i13/2 SE, the amplification range is reduced to the longer wavelength part of the transition, over 1.31µm (fig.). On the contrary, the 4F3/2 → 4I11/2 transition around 1.05 µm is not perturbed by ESA.
© 1998 IEEE
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