Abstract

Nd³⁺ doped optical fibers are interesting medium for both laser emission and amplification in the near infrared. The stimulated transitions start from the ⁴F_3/2 level. However higher energy levels above ⁴F_3/2 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 ⁴F_3/2 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 ⁴I_9/2 → ⁴F_3/2 For the ⁴F_3/2 → ⁴i_13/2 SE, the amplification range is reduced to the longer wavelength part of the transition, over 1.31µm (fig.). On the contrary, the ⁴F_3/2 → ⁴I_11/2 transition around 1.05 µm is not perturbed by ESA.

© 1998 IEEE