Ultrafast time-resolved measurements of excited state relaxation in Ce/sup 3+/-doped LiSrAlF/sub 6/ and LiCaAlF/sub 6/

Summary form only given. The gain spectra of Ce/sup 3+/-doped LiSrAlF/sub 6/ (Ce:LiSAF) and LiCaAlF/sub 6/ (Ce:LiCAF) at 280-320 nm (>4000 cm/sup -1/) are characteristic of the Ce/sup 3+/ 5d/sup 1/-4f/sup 1/ interconfigurational transition. The lowest /sup 2/F energy state of Ce/sup 3+/ has a single 4f electron. The spatially diffuse 5d electron orbital extends outwards from the ion and the optical spectra of Ce/sup 3+/ depend strongly on the crystal field splitting of the /sup 2/D free-ion excited state. In YAG where the separation of the five levels belonging to /sup 2/D is relatively large, fast relaxation between the lowest two levels has been observed, but the methods used (excited state absorption, growth of the yellow-green or decay of the UV emission) employed 60-ps pulses which allowed only an upper (and inaccurate) limit of 5 /spl plusmn/ 5 ps to be estimated. In Ce:LiSAF and Ce:LiCAF the /sup 2/D splitting is much weaker, and cannot be seen in the absorption spectra at room temperature. Using femtosecond pulses and pump and probe technique we observed ultrafast (<500 fs) relaxation in /sup 2/D in Ce:LiSAF and Ce:LiCAF.