Disentangling electrons and lattice nonlinear optical response in metal-dielectric Bragg filters

We investigate by broadband femtosecond pump-probe spectroscopy the transient optical response of a metaldielectric Bragg filter (MDBF) made of thin layers of gold and fused silica. A quantitative comparison of the experimental resultswith a semiclassical modelwith no fitting parameters allows us to disentangle all the different contributions to the transient optical response of the MDBF, which include the ultrafast dynamics of thermalized and nonthermalized electrons as well as of lattice phonons excited in the metal layers. Furthermore, we provide a quantitative comparison of the optical response of the MDBF with that of a single gold layer under comparable excitation conditions. The results clearly show the advantages and disadvantages of the multilayer configuration in terms of all-optical-modulation capability.