Photon echo of an ultranarrow optical transition of ¹⁶⁷Er³⁺ in ⁷LiYF₄ crystals

The longitudinal and transverse relaxation times for a transition between hyperfine sublevels of the lower electronic states of the ⁴I_15/2 and ⁴I_9/2 multiplets of ¹⁶⁷Er³⁺ ions in ⁷LiYF₄ crystals have been determined for the first time using two-pulse and stimulated photon echo measurements in zero magnetic field at a temperature of 4 K. The decay of the photon echo signal has been shown to be modulated, which is tentatively attributed to the superhyperfine interaction of the ¹⁶⁷Er³⁺ ions with their ¹⁹F⁻ nearest neighbours. The contributions of various types of interaction to the ultranarrow linewidth (∼24 MHz) of the transition in question are discussed. Our results demonstrate that this optical transition of the ¹⁶⁷Er³⁺ ion in ⁷LiYF₄ crystals is potentially attractive for use in Raman quantum memory schemes. (paper)