The surface plasmon polariton (SPP), induced when a laser field is irradiated on a given geometry of a nanostructure, has an important influence on the strong-field dynamics, which recently has attracted much more attention.

Researchers at Shanghai Institute of Optics and Fines Mechanics (SIOM/China) investigated the propagation of a spatially inhomogeneous few-cycle laser field, linked to surface plasmon polaritons, through an ensemble of quantum wells under two conditions. It is found that the transmitted spectra sensitively depend on the spatial inhomogeneity due to the nonlinear propagation effects. Under the small-frequency mismatch condition, the transmitted spectral distribution is continuous for the spatially homogeneous case. However, when spatial inhomogeneity is introduced, the distribution is discrete instead, with clearly even- and odd-order harmonic peaks coexisting, which is related to the strong-field reshaping effect and the inversion symmetry breaking due to the introduction of the spatially inhomogeneous field. As for the large-frequency mismatch condition, only odd-order harmonics exist, no matter how strong the spatial inhomogeneity is. Under both conditions, the propagation effect can obviously enhance the intensity of higher spectral components. [Phys. Rev. A 88, 035805,2013]