Optical excitation of metallic nanostructures induces strong intraband transitions, leaving transient depletion below the Fermi level, which allows transient interband transition to this depletion band. This is equivalent to the lowering of the threshold for interband transitions and pushes the plasmonic band to the red. As a result, localized surface plasmon resonance (LSPR) is “extinguished” or “quenched” around the bandedge, in contrast, the interband optical absorption becomes enhanced and redshifted. The corresponding transient absorption (TA) signals have equal lifetimes and opposite signs. Moreover, the TA spectrum is found to be a second-order differential of the steady-state optical extinction spectrum over the studied band. This is a commonly existing mechanism for metallic nanostructures and verified with gold in this work. Such a discovery is completely different from the optical-excitation-induced redshift of LSPR through enhanced electronic scattering and is important for understanding the ultrafast spectroscopic response of plasmonic nanostructures with clear photophysical insights, supplying solid basis for exploring optical logic device and optical data processing techniques.

中文翻译：

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通过边带移动进行的等离子熄灭被识别为二​​阶光谱差异

金属纳米结构的光激发引起强烈的带内跃迁，使瞬态损耗降至费米能级以下，从而允许瞬态带内跃迁至该损耗带。这等效于降低带间过渡的阈值并将等离激元带推向红色。结果，局部表面等离子体激元共振（LSPR）在带边缘周围被“熄灭”或“猝灭”，相反，带间光吸收变得增强并发生红移。相应的瞬态吸收（TA）信号具有相同的寿命和相反的符号。此外，发现TA光谱是所研究频带上稳态消光光谱的二阶微分。这是金属纳米结构的一种普遍存在的机制，并且在这项工作中用金进行了验证。