Spatially Resolved Nonlinear Plasmonics

Nonlinear optical plasmonics investigates the emissionof plasmonicnanoantennas with the aid of nonlinear spectroscopy. Here we introducenonlinear spatially resolved spectroscopy (NSRS) which is capableof imaging the k-space as well as spatially resolving the THG signalof gold nanoantennas and investigating the emission of individualantennas by wide-field illumination of entire arrays. Hand in handwith theoretical simulations, we demonstrate our ability of imagingvarious oscillation modes inside the nanostructures and thereforespatial emission hotspots. Upon increasing intensity of the femtosecondexcitation, an individual destruction threshold can be observed. Wefind certain antennas becoming exceptionally bright. By investigatingthose samples taking structural SEM images of the nanoantenna arraysafterward, our spatially resolved nonlinear image can be correlatedwith this data proving that antennas had deformed into a peanut-likeshape. Thus, our NSRS setup enables the investigation of a nonlinearself-enhancement process of nanoantennas under critical laser excitation.