Experimental observation of spectral diffusion in an optically pumped Er^{3 +}: Y₂ SiO₅ crystal

We report on experimental observations of spectral diffusion mechanisms occurring in an optically pumped erbium-doped Y₂ SiO₅ crystal. The diffusion is characterized using photon echo spectroscopy on the ⁴I_{15 / 2} → ⁴I_{13 / 2} transition. Optical pumping creates population inversion on the transition before the echo sequence. Spectral diffusion is then studied under different population inversion conditions. These observations raise new questions on the spectral diffusion mechanisms.