I got propagation methods and looked into RCWA algortihms, also I suppose you pointed me to FDFD because laser itself is a monochromatic wave.
I am not sure RCWA can provide what I need ; define a geometry with specific permeability,permittivity and conductivity parameters (multiple layers), apply an ELF field from one side of the medium and look into refraction index changes from the outer side (which is laser contact point) ? Assuming the medium model is very precise, is this theoretically calculateable ? can one derive a symbolic solution to this problem ? Medium is dispersive, anisotropic and nonlinear.