Abstract
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.
Highlights
Nanophotonics is closely related to human life, especially due to occurrences of revolutionary developments in optics-based reliable, cost-effective, efficient, and compact technologies in society
The configuration of dark field scattering spectrum (DFSS) with an unpolarized white light source will inevitably lead to the undesirable inhomogeneous broadening of full width at half maximum (FWHM) because of film–NP and interparticle coupling effects [Fig. 2(b)]
Nonlinear nanorulers can accomplish ∼1 nm resolutions. These results demonstrate that plasmon-enhanced SHG (PESHG) characterization can exhibit its superiority in spectral accuracy and signal-to-noise ratios for obtaining the quantitative description of PESHG intensities against gap-sizes in the subtle range, enabling us to sensitively characterize slight changes of surface plasmons
Summary
Nanophotonics is closely related to human life, especially due to occurrences of revolutionary developments in optics-based reliable, cost-effective, efficient, and compact technologies in society. The extinction efficiency curve or reflection efficiency curve will exhibit one or more of the extrema.29,31,32 In light of such features of SPR, optical characterization methods, such as reflection/transmission spectrum, scanning near-field optical microscope (SNOM), dark field scattering spectrum (DFSS), Raman/fluorescence spectroscopy (SERS/SEF), and tip-enhanced Raman/fluorescence spectroscopy (TERS/TEF), can effectively establish the sensitive characterization of SPs. difficulties remain in detecting high-order plasmonic modes and probe-induced invasive interferences. Our research group has managed to combine SERS and DFSS techniques to indirectly characterize the optical excitation and near-field enhancement characteristics of plasmon-induced magnetic resonance (PIMR).46 This method requires the introduction of Raman probe molecules, which will undoubtedly disturb SPR characteristics of the system itself, resulting in nonignorable signal interference and distortion. The conclusion along with our perspective for readers’ reference is drawn
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