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Ultrafast relaxation dynamics in bimetallic plasmonic catalysts
摘要： Combining a plasmonic metal, such as gold, with other popular catalysts, such as Ni or Pt, can extend its benefits to many energy-extensive reactions catalyzed by those metals. The efficiency of a plasmon-enhanced catalytic reaction is mainly determined by the light absorption cross section and the photo-excited charge carrier relaxation dynamics of the nanoparticles. We have investigated the charge carrier relaxation dynamics of gold/nickel (Au/Ni) and gold/platinum (Au/Pt) bimetallic nanoparticles. We found that the addition of Ni or Pt to gold can reduce light absorption in gold nanoparticles. However, electron–phonon coupling rates of Au/Ni and Au/Pt nanoparticles are significantly faster than that of pure Au nanoparticles. This is due to the fact that both Ni and Pt possess significantly larger electron–phonon coupling constants and higher densities of states near the Fermi level in comparison with Au. Additionally, the phonon–phonon coupling rate of bimetallic Au/Pt and Au/Ni nanoparticles was significantly different from that of pure gold nanoparticles, due to the acoustic impedance mismatch at the nanoparticle/substrate interface. Our findings provide important insights into the rational design of bimetallic plasmonic catalysts.
关键词： bimetallic nanoparticles,ultrafast relaxation dynamics,electron–phonon coupling,phonon–phonon coupling,plasmonic catalysts
更新于2025-09-23 15:21:01
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Dual-comb-based asynchronous pump-probe measurement with an ultrawide temporal dynamic range for characterization of photo-excited InAs quantum dots
摘要： A dual-comb-based asynchronous optical sampling (ASOPS) pump-probe measurement system is demonstrated for characterizing the relaxation dynamics in a photo-excited self-assembled InAs quantum dot (QD) semiconductor. Although the photo-excited QD material has multiple complex relaxation processes, the transient transmittance responses (from femtoseconds to nanoseconds) are successfully obtained within a sub-second short acquisition time by using the ASOPS system. This is achieved with high stability and an extremely wide temporal dynamic range of approximately 105. The utility of the developed system is demonstrated as a powerful and easy-to-use measurement tool for studying the complex photo-excited dynamics of QD materials.
关键词： dual-comb,asynchronous optical sampling,InAs quantum dots,pump-probe measurement,relaxation dynamics
更新于2025-09-23 15:21:01
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Nonlinear optics at excited states of exciton polaritons in two-dimensional atomic crystals
摘要： Exciton polaritons (EP) are partial-light partial-matter quasiparticles in semiconductors demonstrating striking quantum phenomena such as Bose-Einstein condensation and single-photon nonlinearity. In these phenomena, the governing process is the EP relaxation into the ground states upon excitation, where various mechanisms are extensively investigated with thermodynamic limits. However, the relaxation process becomes drastically different and could significantly advance the understanding of EP dynamics for these quantum phenomena, when excited states of EP are involved. Here, for the first time, we observe nonlinear optical responses at the EP excited states in a monolayer tungsten disulphide (WS2) microcavity, including dark excited states and dynamically metastable upper polariton band. The nonlinear optics leads to unique emissions of ground states with prominent valley degree of freedom (DOF) via anomalous relaxation process, which is applicable to a wide range of semiconductors from monolayer transition metal dichalcogenides (TMDs) to emerging halide perovskites. This work promises possible approaches to challenging experiments such as valley polariton condensation. Moreover, it also constructs a valley-dependent solid state three-level system for terahertz photonics and stimulated Raman adiabatic passage.
关键词： excited states,exciton-polaritons,relaxation dynamics,Nonlinear optics,monolayer transition metal dichalcogenide
更新于2025-09-16 10:30:52
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Plasma formation and relaxation dynamics in fused silica driven by femtosecond short-wavelength infrared laser pulses
摘要： Laser-induced plasma formation and subsequent relaxation in dielectric solids is the precursor to structural modi?cations serving as the basis for direct laser writing of functional optical micro- and nanostructures. Based on an experimental arrangement combining a time-resolved transmission measurement with a cross-phase modulation measurement, we isolate the plasma formation and relaxation dynamics in the bulk of amorphous fused silica excited by femtosecond short-wavelength infrared (k ? 2100 nm) laser pulses. Whereas the relaxation time of the generated subcritical electron-hole plasma was so far assumed to be constant, our ?ndings indicate an intensity-dependent relaxation time. We attribute this intensity dependence to vibrational activation of the medium, leading to detrapping of trapped carriers and a reduced trapping probability.
关键词： plasma formation,femtosecond laser pulses,relaxation dynamics,fused silica,short-wavelength infrared
更新于2025-09-12 10:27:22