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Ultrasensitive and ultrafast nonlinear optical characterization of surface plasmons

Amid the rapid development of nanosciences and nanotechnologies, plasmonics has emerged as an essential and fascinating discipline. Surface plasmons (SPs) lay solid physical foundations for plasmonics and have been broadly applied to ultrahigh-resolution spectroscopy, optical modulation, renewable energy, communication technology, etc. Sensitive optical characterizations for SPs, including far/near-field optics, spatial-resolved spectroscopy, and time-resolved behaviors of SPs, have prompted intense interest in diverse fields. In this Research Update, the ultrasensitive optical characterization for sub-radiant SPs is first introduced. Then, distinct characterization methods of nonlinear plasmonics, including plasmon-enhanced second harmonic generation and plasmon-enhanced sum frequency generation, are demonstrated in some classical nanostructures. Transient optical characterizations of SPs are also demonstrated in some well-defined nanostructures, enabling the deep realization of time-resolved behaviors. Finally, future prospects and efforts of optical characterization for SPs are proposed.