Excitation of surface plasmon polaritons on silicon with an intense femtosecond laser pulse

摘要

We report the experimental observation of anomalies appearing in the reflection of intense p-polarized 100- femtosecond (fs) laser pulses at a nonmetallic material surface with a grating structure. The reflectivity was measured in air as a function of the angle of incidence at a Si grating. The results have exhibited an abrupt decrease to create a sharp dip at a specific incident angle of ～24°, where the grating surface was deeply ablated along the edge of the grooves. Similar to the so-called Wood’s anomalies, the observed angle-dependent reflectivity provides direct evidence that surface plasmon polaritons (SPPs) can resonantly be excited at the interface between air and the nonmetallic material surface, as the intense fs laser pulse produces a high density of free electrons to form a metal-like layer on the Si grating surface. Calculation for a model target reproduces well the experimental results to confirm the excitation of SPPs on the Si grating, demonstrating the generation of enhanced near fields for the periodic ablation of a target surface.