Four-wave mixing ofNd3+-doped crystals and glasses

Degenerate four-wave-mixing measurements have been performed on a wide variety of ${\mathrm{Nd}}^{3+}$-doped oxide and fluoride glasses and crystals. Crossed beams from a cw argon-ion laser were used to excite the ${\mathrm{Nd}}^{3+}$ ions directly and establish population gratings. Absolute measurements of the signal strengths were made, and their magnitudes were found to be sensitively influenced by the composition of the host. A theoretical model was developed to interpret the results, and it was found that the dominant contribution to the signal is associated with the difference in polarizability of the ${\mathrm{Nd}}^{3+}$ ions in the metastable state versus the ground state. The magnitude of the observed change in the polarizability indicates that the 4f→5d transitions are responsible for this effect, and as a result, the value of the 〈4f‖r‖5d〉 radial integral sensitively affects the calculated polarizability change.