Laser-induced instantaneous spectral diffusion inTb3+compounds as observed in photon-echo experiments

We have observed a significant ‘‘instantaneous spectral diffusion’’ phenomenon in photon-echo experiments on ${\mathrm{Tb}}^{3+}$:${\mathrm{LiYF}}_4$. This laser-induced effect makes observed optical dephasing rates intensity dependent and can also contribute a frequency dependence to the measured rates. A change in the magnetic dipole-dipole interaction between ${\mathrm{Tb}}^{3+}$ echo ions and surrounding ${\mathrm{Tb}}^{3+}$ ions occurs when surrounding ions are excited. This causes an instantaneous shift in the optical frequency of the echo ion that lasts for ${\mathit{T}}_1$∼1 msec. Frequency shifts caused by the first excitation pulse have no effect on echo rephasing (${\mathit{T}}_1$≫${\mathit{T}}_2$), but those caused by the second pulse prevent proper echo rephasing. A summary is given of other ion-lattice and ion-ion interactions that can cause similar laser-induced effects in a wide variety of insulating compounds. There is potential for probing the nature of inhomogeneous broadening.