ECHOES IN LaF 3 : Nd 3 + AND YAG

We report the observation of photon echoes for the 41 4F 9/z312 transition of Nd3+ in both lanthanum trifluoride and yttrium aluminum garnet. Previously, echoes in this transition have only been observed in calcium tungstate [ I]. We compare the dependence of the echo signals in these crystals on sample temperature and applied magnetic field. In all three crystals, the ground state 419,2 is split into five Kramers doublets (Z, -Z,) and the 4F3,2 state into two doublets (RI and R2) as shown in fig. ,1 [2-41. The echoes were excited between the Zl and RI levels. Our samples were: LaF3:Nd3+ (0.1 atom %), CaWO,: Nd3+ (0.1 atom %, uncompensated), and YAG: Nd3+ (0.7 atom %), with transition frequencies corresponding to 8626 A [2 1, 8767 A [3], and 8749 A [4], respectively. The experimental arrangement was similar to ref. [l] except that the excitation laser pulses were collinear and consequently the echoes were also emitted collinearly. A three-stage Kerr cell optical shutter prevented the photomultiplier detector from saturating. The laser E-field was vertical. The LaF3 and CaWO, samples were oriented with the c-axis perpendicular to both the E-vector and the direction of propagation to maximize the echo signal. The sample temperature was varied between 3°K and 20”K, and a magnetic field variable up to 3 kG was ap plied along the c-axis. The shot-to-shot signal fluctuation was typically a factor of two.