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1D wave-mechanical simulation of surface plasmon polariton propagation at a gold-vacuum interface. The static regime as well as the delay-dependent propagation signature are well reproduced
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Time-resolved imaging of the propagation and interference of isolated ultrashort surface plasmon polariton wave packets is demonstrated using two photon photoemission microscopy. The group- and phase velocity of individual wave packets are determined experimentally. Using two counter-propagating surface plasmon polariton pulses, the transient forma...
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Citations
... In a quantum description, such a fringe modulation must be attributed to quantum path interferences in the electron emission process, as shown in a recent experiment [52] on spin-orbit mixing of SPPs with orbital angular momentum [53] and circularly polarized light. Since the period length of the fringe pattern is determined by the SPP wavelength SPP , the pattern is commonly referred to as a "direct conceptual visualization" of the SPP pulse [43], [54]. A profile taken through the fringe pattern, however, shows a distinct nonlinearity ( Figure 2B), which appears as a second-order cross-correlation of the pulses. ...
Quantum path interferences occur whenever multiple equivalent and coherent transitions result in a common final state. Such interferences strongly modify the probability of a particle to be found in that final state, a key concept of quantum coherent control. When multiple nonlinear and energy-degenerate transitions occur in a system, the multitude of possible quantum path interferences is hard to disentangle experimentally. Here, we analyze quantum path interferences during the nonlinear emission of electrons from hybrid plasmonic and photonic fields using time-resolved photoemission electron microscopy. We experimentally distinguish quantum path interferences by exploiting the momentum difference between photons and plasmons and through balancing the relative contributions of their respective fields. Our work provides a fundamental understanding of the nonlinear photon–plasmon–electron interaction. Distinguishing emission processes in momentum space, as introduced here, could allow nano-optical quantum-correlations to be studied without destroying the quantum path interferences.
... Figure 3(a) compares the experimentally extracted values with the frequency-resolved group velocity predicted from the optical properties of gold, 32 which coincide with previous studies. 17,18,33 The cross-correlation signals at the apices permit extraction of the SPP spectra, as shown in Figure 3(b). While in the case of copropagation the almost complete light spectrum is transmitted to the plasmonic wavepacket, the counter-propagating SPP's bandwidth is distinctly narrowed, and its center frequency is red- shifted by 15 THz. Figure 3(c) presents the frequency dependent field coupling efficiencies η f ield (ω) with respect to the laser spectrum (detailed derivation of η f ield (ω) is provided in section 5 of Supporting Information). ...
Surface plasmon polaritons (SPPs) can confine and guide light in nanometer volumes and are ideal tools for achieving electric field enhancement and the construction of nanophotonic circuitry. The realization of the highest field strengths and fastest switching requires confinement also in the temporal domain. Here, we demonstrate a tapered plasmonic waveguide with an optimized grating structure that supports few-cycle surface plasmon polaritons with >70 THz bandwidth while achieving >50% light-field-to-plasmon coupling efficiency. This enables us to observe the—to our knowledge—shortest reported SPP wavepackets. Using time-resolved photoelectron microscopy with suboptical-wavelength spatial and sub-10 fs temporal resolution, we provide full spatiotemporal imaging of co- and counter-propagating few-cycle SPP wavepackets along tapered plasmonic waveguides. By comparing their propagation, we track the evolution of the laser-plasmon phase, which can be controlled via the coupling conditions.
... Electrons are subsequently collected using electron objective/projective and an electron sensitive camera in a low-energy electron microscope, providing the necessary nm spatial resolution. In the past, this technique has been applied to image the dynamics of both LSPs and SPPs in metallic nanostructures, [91][92][93][94][95][96][97] providing also a way to understand more deeply the most important factors in plasmon damping. 98 Furthermore, TR-PEEM has been used to study nanofocusing of SPPs, 99 with many potential applications including heat-assisted magnetic recording, 100 or plasmon-induced electron emission. ...
In the past 20 years, we have reached a broad understanding of many light-driven phenomena in nanoscale systems. The temporal dynamics of the excited states are instead quite challenging to explore, and, at the same time, crucial to study for understanding the origin of fundamental physical and chemical processes. In this review, we examine the current state and prospects of ultrafast phenomena driven by plasmons both from a fundamental and applied point of view. This research area is referred to as ultrafast plasmonics and represents an outstanding playground to tailor and control fast optical and electronic processes at the nanoscale, such as ultrafast optical switching, single photon emission, and strong coupling interactions to tailor photochemical reactions. Here, we provide an overview of the field and describe
the methodologies to monitor and control nanoscale phenomena with plasmons at ultrafast timescales in terms of both modeling and experimental characterization. Various directions are showcased, among others recent advances in ultrafast plasmon-driven chemistry and multi-functional plasmonics, in which charge, spin, and lattice degrees of freedom are exploited to provide active control of the optical and electronic properties of nanoscale materials. As the focus shifts to the development of practical devices, such as all-optical transistors, we also emphasize new materials and applications in ultrafast plasmonics and highlight recent development in the relativistic realm. The latter is a promising research field with potential applications in fusion research or particle and light sources providing properties such as attosecond duration.
... [75] This is the basis for interferometric time-resolved photoemission electron microscopy (ITR-PEEM) imaging of SPP dynamics on the nanofemto scale. [75,108,124,135,136,[138][139][140]. ...
... The lithographic design of SPP coupling metastructures can define various functions, such as the SPP focusing in space and time, the OAM carried by an SPP field, the SPP standing and propagating waves in resonators, etc. [125][126][127]134,[140][141][142] The design of OAM is particularly interesting in topological plasmonics, because it defines the spin-orbit coupling of propagating SPP fields. [103,107,108,129,143] It is also significant that optical spin affects the SPP coupling. ...
Light at optical frequencies interacting with a metal surface can excite interband quantum transitions, or intraband currents at frequencies approaching the PHz range. Momentum conservation enables the interband excitation to occur in first order as a dipole transition, while intraband excitations involve second-order momentum scattering processes. The free electron response to optical fields can also be collective, causing the optical field to be screened by the multipole plasmon response. We describe the exitation of single crystal silver surfaces in the region where the dielectric response transits from negative to positive passing through the epsilon near zero (ENZ) condition. There, electrons can no longer screen the optical field, so that it penetrates as a collective charge density wave of the free electron plasma, in other words, as a bulk transverse or longitudinal plasmon field. We examine two-photon photoemission (2PP) signals from Ag(1 1 1), (1 0 0) and (1 1 0) surfaces through the ENZ region under conditions where intraband, and interband single particle, and bulk plasmon collective responses dominate. We are specifically interested in the bulk plasmon decay into plasmonic photoemission. Plasmonic decay into excitation of electrons from the Fermi level, which we observe as a nonlinear 2PP process, has been established for the free electron and noble metals, but its significance to transduction of optical-to-electronic energy has not penetrated the plasmonics community. 2PP spectra show evidence for intraband hot electron generation, interband surface and bulk band excitation, and nonlinear bulk plasmon driven plasmonic single particle excitation. Because the intraband and plasmonic decay into hot electron distributions have been extensively considered in the literature, without reference to explicit experimental measurements, we discuss such processes in light of the directional anisotropy of the electronic structure of single crystalline silver. We note that projected band gaps in silver exclude large regions of the unoccupied state density from hot electron generation, such that it predominantly occurs in the (1 1 0) direction. Moreover, the excited hot electron distributions do not follow expectations from the joint density of the occupied and unoccupied states of a free electron metal, as assumed in majority of research on hot electron processes. We describe the strongly anisotropic hot electron distributions recorded by 2PP spectroscopy of Ag surfaces, and the plasmonic photoemission process that occurs on all surfaces irrespective of the momentum-dependent single particle band structure of silver. Plasmonic photoemission, or its linear analog that excites hot electrons at energies below the work function of Ag, is an important process for harvesting hot electron energy in photocatalytic and electronic device applications because the plasmon energy is not distributed between an electron and hole. This plasmonic decay channel is robust, but many aspects raise further questions. The accompanying publication by Gumhalter and Novko discusses the plasmonic photoemission from a theoretical point of view and its extension to Floquet engineering, as an exploration of novel plasmonic excitation processes in metals.
... We note that the latter approach is widely employed in classical photonics and plasmonics in equilibrium situations, provided that the response of the material remains localized in space [126]. It should also be mentioned that recent progress in time-resolved photoemission electron microscopy using ultrashort laser excitation sources enables a mapping of plasmon polaritons that deepens our understanding and interpretation of the plasmonic behavior [127]. [110] for measuring the optical-field-induced current in fused silica. ...
Short and ultrashort laser pulses are nowadays an integral part of up-to-date technological solutions in many areas from material micro-/nanoprocessing and synthesis of new materials to quantum computing and biomedicine. The number of laser applications in science and industries is growing precipitously with tendencies of enhancing laser processing precision and reproducibility toward creation of extremely tiny objects. Coupling more laser energy into a smaller material volume in a controllable way is one of the grand challenges, which can only be achieved through a deep understanding of a wealth of the laser-triggered transient processes at different spatiotemporal scales.
The objective of this chapter is to provide a review of the main fundamental linear and nonlinear processes excited by ultrafast lasers in different kinds of materials with the aim to reveal and highlight possible mechanisms, which would enable extreme localization of energy absorption. After summarizing existing knowledge on laser-induced phenomena that includes mechanisms of laser light absorption, heat transfer peculiarities, energy thermalization at ultrafast time scales, and related hydrodynamic phenomena, an overview is given on novel insights into highly nonequilibrium processes gained in recent years via quantum and molecular dynamics simulations. The fundamental part is followed by an analysis of possible techniques and processes, which could enable extreme localization of laser energy absorption both on the surface of material samples and in the bulk. Finally, as an example of laser energy localization alternating at nanoscale, laser-induced periodic surface structures (LIPSS) are discussed. The multiplicity of the mechanisms is demonstrated via a rigorous theoretical analysis and simulations.
... The full width at half maximum of the focus spot of ≈170 nm is well below the diffraction limit for S ≈ 780 nm SPPs and is already indicative of the nonlinear character of the electron emission process. With a spiral radius of r 0 = 12.5 μm and a SPP group velocity of 93.6% of the speed of light in vacuum [31] the SPP propagates for 45 fs to the focus, which implies that at the time the focus is formed, the <15 fs short exciting laser pulse has already left the surface and does not contribute to the field strength at the time of electron emission. As such, the electron yield is entirely caused by plasmoemission. ...
Spectroscopic photoemission microscopy is used to detect and quantify a ponderomotive shift in the energy of electrons that are emitted from a surface plasmon polariton focus. The focus is formed on an atomically flat Au(111) surface by an Archimedean spiral and is spatiotemporally separated from the circularly polarized light pulse used to excite the spiral. A spectroscopic analysis of electrons emitted from the focus exhibits a peaked above-threshold electron emission spectrum. From the shift of the peaks as function of laser power the field strength of the surface plasmon polariton was quantitatively determined without free parameters. Estimations of the Keldysh parameter γ = 4.4 and the adiabaticity parameter δ = 4700 indicate that electron emission occurs in a regime of multiplasmon absorption and nonlocalized surface plasmon fields.
... In this configuration, due to the oppositely signed field and plasmon wave vectors, SPPs propagate and can be imaged without interference with the driving excitation laser field, which normally results in self-interference near-field emission patterns, 10,12 as exemplified by normal incidence PEEM measurements. 13,29,30 Ultrafast PEEM has been applied in various contexts for investigating the near-field response of plasmonic structures. 10,12,27,31 Here, we employ phase-locked, femtosecond pulse pairs in the counter-propagating geometry to launch SPPs from a series of lithographically patterned 2PGs with well-defined pitches and hole diameters. ...
... This mismatch is on the order of a few percent at optical frequencies and is readily accomplished through scattering from surface structures such as individual holes or trenches. 9,10,13,29,32 In contrast, 2PG couplers add additional tunable in-plane momentum as determined by the grating pitch. Our experiments utilize 2PG couplers of different pitches between 385 and 420 nm prepared by focused ion beam milling holes of varying diameters in a 15 Â 15 square lattice configuration into 100 nm thick silver sputtered over freshly stripped mica. ...
The role of surface plasmon polaritons (SPPs) in nanohole array optical extinction spectra is explored using a time-resolved technique capable of isolating the air/metal interfacial SPP contribution to the typical Fano profile in optical transmission curves. A pair of interferometrically locked broad-band femtosecond pulses is used to launch SPPs from lithographically patterned plasmonic nanohole arrays. SPPs launched in the co- and counter-propagating directions are probed using a third probe pulse in a photoemission electron microscope. Using this approach, we record interferometric SPP–SPP linear autocorrelations that selectively report on the resonances of SPPs launched from arrays of varying pitches and hole diameters. Aside from advancing an approach to selective SPP spectroscopy, we illustrate that resonant coupling in the counter-propagating direction may be exploited to control the spatial, temporal, and spectral characteristics of SPPs. For the counter-propagating direction, we show that tuning the array pitch near the fundamental plasmon resonance generates color-tuned (∼770–820 nm), narrow bandwidth SPPs, and the bandwidth may be controlled by changing the ratio of pitch to hole diameter. The SPP resonances we recover through Fourier transforms of the interferometric autocorrelations shed light on the classical problem of Fano interference in nanohole array extinction spectra.
... The insets in Figure 4d-f show the FDTD images that show good consistency with experiments in Figure 4a-c. The images are calculated from Y ∝ ∫ ðE k Þ 4 dt, [33][34][35][36] as the fourth power of the in-plane electric field component at the Cd 3 As 2 Àvacuum interface. The simulated images of the 4.8 μm-diameter microdisk and 5 μm-diameter microdisk have a dark spot and bright spot at the center, whether linearly polarized or circularly polarized excited ( Figure S7, Supporting Information), which is consistent with the experiment result due to the constructive (destructive) interference. ...
Resolving the photonic modes in real space is essential to understand the fundamental process and control of photonic behavior in optoelectric devices. However, the understanding of the photonic modes of semimetal Cd3As2 is still lacking. Herein, the quasicylindrical waves (QCW) on Cd3As2 nanoplates using photoemission electron microscopy (PEEM) are found out. The QCW is due to the optical field scattered by subwavelength indentations, with wavelength being the same as the incident light, and their amplitude decays as r−1/2 from the edges. The transverse magnetic (TM) mode dominates the observed QCW of Cd3As2 nanoplates, which is affected by the edge structure. In broadband from UV to visible, the QCWs on Cd3As2 nanoplates are observed. Further, nanostructures to achieve subwavelength focusing and interference lattice of the Cd3As2 optical QCW are achieved. These findings demonstrate the regulation of QCW, which benefits optimizing the optoelectronic performances of semimetal materials in the future.
... Surface plasmon polaritons (SPPs) [1,2] have received a great deal of attention largely because of their promise for use in next-generation, miniaturized electronic circuits [3,4] and integrated optical devices [5,6]. SPPs are attractive information carriers as they comprise propagating electro-magnetic fields coupled to charge density fluctuations at the surface of metals, with group velocities near the speed of light in a vacuum [7][8][9]. Combining the size of nanoelectronics with the speed and high bandwidth of dielectric photonics, SPPs can enable devices that can naturally interact with both technologies allowing for powerful, ultracompact, on-chip photonic circuits for rapid data transmission and signal processing. Surface plasmon-based wavelength demultiplexing is one of the key topics in plasmonics and plays a crucial role in relevant applications such as all-optical communication [10], plasmon-assisted sensing, and imaging [11,12]. ...
A compact plasmonic wavelength demultiplexer is an essential prerequisite for practical applications, including the next-generation on-chip devices, near-field optical trapping, and micromanipulation. However, alleviating the polarization dependence of the wavelength demultiplexers remains one of the most challenging issues in realizing such a plasmonic device. Here we propose a gold disk-slit-based compact Fano-type nanoantenna capable of launching surface plasmon polaritons (SPPs) directionally when irradiated under different wavelengths of light, realizing a wavelength demultiplexing function. More importantly, our simulation results show that the shortage of requirement of specific light polarization direction excitation in such wavelength demultiplexers can be circumvented. Furthermore, it is found that the output channel of the SPP can be switched in multiple directions under different polarization excitations. In addition, the results show that the applicable wave band of the wavelength demultiplexing device can be flexibly adjusted by changing the size of the nanoantenna. The technique of introducing the polarization-tunable function into the wavelength demultiplexers in the plasmonic interconnect application enhances the freedom of information transmission and offers a promising building block for future high-speed and high-bandwidth on-chip optical communication.
... Pump-and probe pulses were created and mutualy delayed in a home-built Pancharatnam's phase stabilized Mach-Zehnder Interferometer. We work in normal-incidence geometry, as described in Refs [34,55]. ...
Nanophotonic platforms such as metasurfaces, achieving arbitrary phase profiles within ultrathin thickness, emerge as miniaturized, ultracompact and kaleidoscopic optical vortex generators. However, it is often required to segment or interleave independent sub-array metasurfaces to multiplex optical vortices in a single nano-device, which in turn affects the device’s compactness and channel capacity. Here, inspired by phyllotaxis patterns in pine cones and sunflowers, we theoretically prove and experimentally report that multiple optical vortices can be produced in a single compact phyllotaxis nanosieve, both in free space and on a chip, where one meta-atom may contribute to many vortices simultaneously. The time-resolved dynamics of on-chip interference wavefronts between multiple plasmonic vortices was revealed by ultrafast time-resolved photoemission electron microscopy. Our nature-inspired optical vortex generator would facilitate various vortex-related optical applications, including structured wavefront shaping, free-space and plasmonic vortices, and high-capacity information metaphotonics.
