There are, recently, remarkable achievements in turning light-matter interactions into strong coupling quantum regime. In particular, room temperature plexcitonic strong coupling in plasmon-exciton hybrid systems can bring promising benefits for fundamental and applied physics. Herein we will review theoretical insights and recent experimental achievements in plexcitonic strong coupling and divide this review into two main parts. The first part will briefly introduce the general field of strong coupling, including its origin and history, physical mechanisms and theoretical models, as well as recent advanced applications of strong coupling, such as the quantum or biochemical devices enabled by optical strong coupling. The second part will zoom in and concentrate on plexcitonic strong coupling by introducing its unique features and new potentials (such as single-particle ultrastrong coupling, strong coupling dynamics in femtosecond scale) and discussing the limitations and challenges of plexcitonic strong coupling, which will also be accompanied by potential solutions such as the microcavity-engineered plexcitonics, spectral hold burning effects, and metamaterial-based strong coupling. Finally, we will summarize and conclude this review, highlighting the future research directions and promising applications.

We have developed a novel strategy of resonant scattering-enhanced photothermal microscopy, where the imaged nanoparticles are near-resonant with the probe light.

We investigated the interferometric scattering (iSCAT) imaging of individual gold nanorods (NRs) near optical resonance under laser light illumination.

Photothermal (PT) microscopy enables the efficient detection of absorbing nano-objects with high sensitivity and stability. The PT signal in the current PT microscopy usually comes from the interaction of the probe laser beam with the heating laser beam-induced thermal lens, and the contribution of the scattering field from the imaged nano-object is usually not taken into account. Here, in this paper, we systematically studied the influence of the scattering field from the imaged nanoparticles on the obtained PT signal by using Ag nanowires (NWs) on a glass substrate surrounded by glycerol as an example. Under the excitation of a heating laser beam at 532 nm wavelength, the rise of local temperature around the Ag NW results in the intensity variation of the interferometric scattering probe light at 730 nm wavelength which includes the scattering light from the Ag NW and the reflection light from the glass−glycerol interface. We found that the PT signal on the NW are positive and negative for the probe beam polarized parallel and perpendicular to the NW axis, respectively. Numerical simulations confirm that the heat-induced intensity variation of the pure scattering light from the NW and the thermal lens-induced intensity increase of the reflection light both contribute to the obtained PT signal. Our work provides the basic guidance for the analysis of PT signal from nano-objects with large scattering cross sections.

The ORCID identification number(s) for the author(s) of this article can be found under https://doi.org/10.1002/admt.202201468.