Terahertz electromagnetic transitions observed within the I-4(15/2) ground multiplet of Er3+ ions in Si

An optically induced terahertz transition within the crystal-field-split ground state of Er3+ ion in Si has been conclusively established. A Si/Si:Er multinanolayer structure, where a single type of Er-related centers dominates, has been used. The study was conducted by pump-probe technique with a free-electron laser. Using the transient grating experimental configuration, we identify an absorption band at lambda approximate to 43.5 mu m and measure the related effective lifetime as tau approximate to 50 ps.