Slow light and photon echoes in the ⁷F₀→⁵D₀ transition of Sm²⁺ in single-crystal BaFCl

Slow light effects induced by transient spectral hole-burning in the ⁷F₀→⁵D₀ transition of Sm²⁺ in BaFCl at 688 nm are reported and a probe pulse delay of 1.25 μs was observed through a 5 mm thick crystal. This delay corresponds to a reduction of the group velocity v_G of the transmitted light to ∼4000 m/s. An analysis of the dependence of the slow light effect on the probe pulse timing indicates some broadening of the spectral hole caused by relatively fast excitation energy transfer. We also demonstrate two-pulse (2PE) and (three-pulse) stimulated photon echoes (SPE) for the first time for Sm²⁺ in the solid state and a homogenous linewidth of 16 kHz (∼2.5·10^-8nm) was obtained at 1.8 K. The echoes in the optically dense medium were very efficient and revealed spectral diffusion on the 100-μs time scale possibly due to flipping of the fluorine and chlorine nuclear spins in the environment of the Sm²⁺ ions. Furthermore, the SPE also indicates relatively fast energy transfer, commensurate with the hole decay.