Z-scan measurements of nonlinear refractive indices of NaT(XO_4)_2 T= Y, La, Gd, Lu and Bi, X= Mo, W, femtosecond laser crystals

摘要

The characterization of the coefficient of the nonlinear optical Kerr effect, the nonlinear refractive index (n_2), of several femtosecond laser crystals with compositions derived by total or partial replacement of D~(2+) in DXO_4, X = Mo or W, is presented. Tetragonal (space group I4 ) Na-based double tungstates NaT(WO_4)_2 (T = Y, La, Gd, Lu and Bi) and double molybdate NaY(MoO_4)_2, as well as the monoclinic (space group C2/c) Li_3Gd_3Ba_2(MoO_4)_8 crystals, have been measured by the z-scan technique. All these crystals present structural local disorder, and among them the tetragonal ones exhibit significant n_2 values, which should allow their efficient laser pulsed operation by Kerr-lens mode locking, especially NaBi(WO_4)_2, 68×10~(16) cm~2/W (for σ light), which is about twice than for the others. This feature is attributed to the high polarizability associated to the lone electron pair of Bi~(3+).