Nonlinear refractive indices of disordered NaT(XO4)2 T=Y, La, Gd, Lu and Bi, X=Mo, W femtosecond laser crystals

The nonlinear refractive index (n2) of several NaT(WO4)2 (T = Y, La, Gd, Lu and Bi) and NaY(MoO4)2 femtosecond laser crystals has been measured using the z-scan technique. These tetragonal crystals with structural local disorder present significant n2 values, which should allow their efficient laser pulsed operation by Kerr-lens mode locking, especially NaBi(WO4)2, 68×10-16 cm2/W (for σ light), which is about twice than for the others. This difference is attributed to the high polarizability associated with the lone electron pair of Bi3+.