Z-scan measurements of nonlinear refractive indices of NaT(XO4)2 T= Y, La, Gd, Lu and Bi, X= Mo, W, femtosecond laser crystals

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 I 4) 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 3 Gd 3 Ba 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, 68x10 -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+ .