The refractive index change that accompanies the color change in a class of thermally stable and fatigue-free organic photochromic molecules is used to probe the picosecond dynamics of grating growth within a solid polymer solution of the material and in an organic solvent. These studies demonstrate the intrinsic picosecond response time of the fulgide by direct measurement of the refractive index change of the chromophore. Additionally, these dynamical studies allow for the quantification of the cycling potential for the material.