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Register a new userLaser Induced Periodic Surface Structures Induced by Surface Plasmons Coupled via Roughness
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Added by
Svetlana V. Gurevich
Publication date
2013
fields
Physics
and research's language is
English
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In this paper the formation mechanisms of the femtosecond laser-induced periodic surface structures (LIPSS) are discussed. One of the most frequently-used theories explains the structures by interference between the incident laser beam and surface plasmon-polariton waves. The latter is most commonly attributed to the coupling of the incident laser light to the surface roughness. We demonstrate that this excitation mechanism of surface plasmons contradicts to the results of laser-ablation experiments. As an alternative approach to the excitation of LIPSS we analyse development of hydrodynamic instabilities in the melt layer.
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We present that surface two-plasmon resonance (STPR) in electron plasma sheet produced by femtosecond laser irradiating metal surface is the self-formation mechanism of periodic subwavelength ripple structures. Peaks of overdense electrons formed by resonant two-plasmon wave pull bound ions out of the metal surface and thus the wave pattern of STPR is carved on the surface by Coulomb ablation (removal) resulting from the strong electrostatic field induced by charge separation. To confirm the STPR model, we have performed analogical carving experiments by two laser beams with perpendicular polarizations. The results explicitly show that two wave patterns of STPR are independently carved on the exposure area of target surface. The time-scale of ablation dynamics and the electron temperature in ultrafast interaction are also verified by time-resolved spectroscopy experiment and numerical simulation, respectively. The present model can self-consistently explain the formation of subwavelength ripple structures even with spatial periods shorter than half of the laser wavelength, shedding light on the understanding of ultrafast laser-solid interaction.
In this Letter we show that the strong coupling between a disordered set of molecular emitters and surface plasmons leads to the formation of spatially coherent hybrid states extended on acroscopic distances. Young type interferometric experiments performed on a system of J-aggregated dyes spread on a silver layer evidence the coherent emission from different molecular emitters separated by several microns. The coherence is absent in systems in the weak coupling regime demonstrating the key role of the hybridization of the molecules with the plasmon.
Understanding the differences between photon-induced and plasmon-induced hot electrons is essential for the construction of devices for plasmonic energy conversion. The mechanism of the plasmonic enhancement in photochemistry, photocatalysis, and light-harvesting and especially the role of hot carriers is still heavily discussed. The question remains, if plasmon-induced and photon-induced hot carriers are fundamentally different, or if plasmonic enhancement is only an effect of field concentration producing these carriers in greater numbers. For the bulk plasmon resonance, a fundamental difference is known, yet for the technologically important surface plasmons this is far from being settled. The direct imaging of surface plasmon-induced hot carriers could provide essential insight, but the separation of the influence of driving laser, field-enhancement, and fundamental plasmon decay has proven to be difficult. Here, we present an approach using a two-color femtosecond pump-probe scheme in time-resolved 2-photon-photoemission (tr-2PPE), supported by a theoretical analysis of the light and plasmon energy flow. We separate the energy and momentum distribution of the plasmon-induced hot electrons from the one of photoexcited electrons by following the spatial evolution of photoemitted electrons with energy-resolved Photoemission Electron Microscopy (PEEM) and Momentum Microscopy during the propagation of a Surface Plasmon Polariton (SPP) pulse along a gold surface. With this scheme, we realize a direct experimental access to plasmon-induced hot electrons. We find a plasmonic enhancement towards high excitation energies and small in-plane momenta, which suggests a fundamentally different mechanism of hot electron generation, as previously unknown for surface plasmons.
Leakage-radiation microscopy of a thin gold film demonstrates the ability of an ensemble of fluorescent diamond nanoparticles attached onto the apex of an optical tip to serve as an efficient near-field surface-plasmon polariton launcher. The implementation of the nanodiamond-based tip in a near-field scanning optical microscope will allow for an accurate control on the launching position, thereby opening the way to scanning plasmonics.
In plasmonic chirality, the phenomenon of circular dichroism for achiral nanoparitcles caused by Coulomb interaction between metal nanoparticles (NPs) and chiral molecules have been studied. At the same time, under the resonance condition, the dye molecules and metal NPs will produce huge Rabi splitting due to strong coupling. If the chiral molecules are at the resonance of the plasmon, what will happen for the strong interaction between the plasmon and molecules with chirality introduced? In this paper, we investigate a spherical core-shell model and analyze its spectral phenomena under the excitation of circularly polarized light (CPL). Based on Coulomb interaction between NPs and chiral molecules, we will show how the various factors affect the strong coupling. We have obtained three mechanisms for the interaction between plasmons and chiral molecules: strong coupling (Rabi splitting up to 243mev), enhanced absorption and induced transparency. The interaction between CPL and chiral molecules with the opposite chirality to CPL is stronger than that of the same chirality, and the line width of the two peaks is closer than that of the same chirality, which shows that for the Rabi splitting with chirality, there are deeper mechanisms for the interaction. This result will be helpful for further research on the interaction between plasmon and molecules with chirality.
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