We report a simple extension of the Z-scan technique that permits a spectral line-shape measurement of the real and the imaginary parts of <i>n</i><sub>2</sub> . In this technique the sample is placed at the peak position of the usual Z-scan curve while the laser frequency is scanned. We employed this method to investigate the nonlinear susceptibility of the R lines of ruby and alexandrite, using a cw dye laser. This susceptibility can be explained by the resonant interaction and by a nonresonant contribution that is due to the difference in polarizability between Cr<sup>3+</sup> excited and ground states. For ruby, the nonresonant contribution to the technique is 1 order of magnitude larger than the resonant contribution. However, for alexandrite both contributions are comparable, and their interference leads to a shift between <i>n</i><sub>2</sub><sup>′</sup> and <i>n</i><sub>2</sub><sup>′′</sup> spectra that is not observed in ruby.
© 2002 Optical Society of America
(190.4400) Nonlinear optics : Nonlinear optics, materials
(190.4720) Nonlinear optics : Optical nonlinearities of condensed matter
(300.6250) Spectroscopy : Spectroscopy, condensed matter
(300.6420) Spectroscopy : Spectroscopy, nonlinear
S. M. Lima, H. Jiao, *L. A. O. Nunes, and T. Catunda, "Nonlinear refraction spectroscopy in resonance with laser lines in solids," Opt. Lett. 27, 845-847 (2002)