Fig. 1. Typical applications of plasmons and the main plasmon effects utilized by these applications

Fig. 2. Excitation and relaxation processes of surface plasmons^[29]. (a) When the light illuminates on the metal nanostructure, the plasmons of the metal nanostructure are excited, causing the surface charges to oscillate collectively; (b) after plasmon excitation, the plasmons quickly undergo spontaneous decoherence processes, therefore energy exchanging from plasmons to high-energy electron-hole pair;(c) in the picosecond range, high-energy electrons and holes are redistributed through electron-electron scattering and electron-phonon scattering to form hot electrons and hot holes of quasi-Fermi-Dirac distribution; (d) lattice is heated, and the heat energy is gradually dissipated through heat exchange with the environment on the nanosecond time scale

Fig. 3. Plasmon resonance of gold nanorods and its photothermal effect (p-polarized incident light illuminates vertically on a single gold nanorod on the surface of the silica substrate from the air side). (a) Surface charge distribution of nanorod; (b) photoelectric field intensity distribution on the surface of nanorods (E is the intensity of local photoelectric field, and E₀ is electric field intensity of incident light field); (c) distribution of joule heat power density Q; (d) maximum temperature change ΔT under nanosecond laser heating for nanorod (laser wavelength is 633 nm, repetition rate is 10 MHz, and power density is 1 mW/μm²); (e) absorption, scattering, and extinction spectra of nanorod (Q_sca is scattering cross-section, Q_abs is absorption cross-section, and Q_ext is extinction cross-section); (f) transient temperature of the nanorod excited by 633 nm nanosecond laser pulses varying with time [pulse width is 40 ns (dashed line and dotted solid line) and 5 ns (solid line)]

Fig. 4. Transient temperature of the nanorod excited by 633 nm femtosecond laser pulses. Temperatures of electrons and lattices are thermal non-equilibrium under femtosecond laser pump (pulse width is 200 fs). The thermal relaxation time of electrons is 10 ps, which is 1/1000 of thermal relaxation time of lattices. The heat capacity, thermal conductivity, and electron-phonon coupling strength of electrons change obviously with electron temperature, therefore increased temperatures of electron and lattice, and excitation power showing significant nonlinear effect

Fig. 5. Absorption of photons in metal^[36]. (a) Transition of electron near the Fermi plane to an empty state on the Fermi plane by absorbing (right) or radiating (left) a phonon during an in-band transition process, resulting in an electron-hole pair, and the momentum change before and after the transition is about the momentum of the absorbed or radiated phonon; (b) a pair of electrons near the Fermi plane produces an in-band transition through the flip scattering process, resulting in two electron-hole pairs with lower energy, and the required momentum changes before and after the transition are provided by the inverse lattice vector of the lattice; (c) in the direct interband transition process assisted by Landau damping, electron-hole pairs are generated near the Fermi surface, and the momenta required before and after the transition are provided by the plasmon; (d) a bound hole is created in the d band and a low energy electron is generated near the Fermi surface in interband transition from d band to sp band

Fig. 6. Microscopic views of PMCR^[5]. (a) Photochemical process; (b) plasmon enhanced electromagnetic fields promote photochemical reactions; (c)(d) excited-carrier mediated photocatalytic reactions; (e) thermochemical reactions induced by local thermal effects

Fig. 7. Chemical reactions mediated by the three typical effects of plasmons^[43,48,51]. (a) Plasmon enhanced electromagnetic field mediated dissociation of the S—S bond in a single (CH₃S)₂ molecule; (b) complete decomposition of water under visible light conditions is realized based on plasmon photocatalyst; (c) localized thermal effect of plasmon structure

Fig. 8. Perspectives on plasmonic chemistry^[46,69,74]. (a) Direct charge transfer from plasmon to semiconductor; (b) plasmonic photoelectrochemistry; (c) plasmonic nanostructures are used for selective activation of reaction sites within molecules

Fig. 9. AI-assisted plasmonic system research (design, synthesis, characterization and performance testing for AI-driven plasmonic structure oriented to application goals)^[10]