Nonlinear Excitation Through Ultrafast Surface Plasmon Polaritons

The success of surface enhanced Raman scattering (SERS) technique suggests that a similar strategy of utilizing field enhancement from localized surface plasmon could open a viable route for probing nonlinear optical signals from single nanoscopic and molecular targets with ultrafast pulses. However, the accompanied nonlinear background and photon-induced melting of metallic nanostructures by ultrafast excitation complicates and hampers the application of nonlinear surface enhanced techniques. In this thesis, a potential approach based on propagating surface plasmon polaritons (SPPs) on planar metallic films is proposed, which could overcome the problems mentioned above while still maintaining the field enhancement benefits of SERS technique. This work demonstrates the feasibility of nonlinear excitation, including two-photon excited fluorescence (TPEF) and four-wave mixing (FWM) of nanoscopic samples, mediated solely by ultrafast SPP fields. For this purpose, a wide-field surface-sensitive FWM microscope based on SPPs is designed and constructed, offering sensitive detection of nonlinear processes near surfaces. In addition, similar nonlinear SPP excitation scheme is achieved with focused surface fields, enabling efficient FWM excitation of single nanoscopic and molecular systems.