We investigate a four-level system in the Er<sup>3+</sup>-doped yttrium aluminum garnet crystal that can produce an absorption or gain doublet in the probe absorption spectrum when driven by a coherent field and incoherent pumping. It is found that the transparent linear positive or negative dispersion can occur between the doublet lines. We show that the group index of a probe pulse can be manipulated when we control the incoherent pumping and the coherent field.
© 2004 Optical Society of America
Jun Qian, Hui-Fang Zhang, Jin-Yue Gao, and Jun Qian, "Positive and negative dispersion in an Er3+-doped yttrium aluminum garnet crystal," J. Opt. Soc. Am. B 21, 1364-1368 (2004)