Surface Plasmon Polariton Pulses Research Articles

High spatiotemporal resolved imaging of ultrafast control of nondiffracting surface plasmon polaritons

Abstract Nondiffracting Bessel surface plasmon polariton (SPP) beams, which have unique self-healing, non-divergence, and linear transmission properties, have charming applications in plasmonic devices and on-chip interconnection circuits. Here we first realize, to the best of our knowledge, the ultrafast control and imaging of the Bessel SPP pulse on the nano-femto scale in the experiment. We demonstrate ultrafast control of Bessel SPP pulse switching by controlling the instantaneous polarization state of the excitation light. Moreover, this variation process is directly mapped on the nano-femto scale by time-resolved two-color photoemission electron microscopy. The results are well reproduced by the finite-difference time-domain (FDTD) method. The current study of ultrafast control and spatiotemporally imaging the switching process establishes an experimental paradigm for revealing the complex mechanisms in ultrafast control of nondiffracting SPP and are useful for developing high-speed, highly-integrated nanophotonic devices, and on-chip circuits.

Controlling surface plasmon polariton losses in the visible spectrum by temperature-induced interband transitions

We study theoretically the temperature dynamics at the metal-dielectric interface excited by a strong pump surface plasmon polariton pulse propagating along it. We demonstrate that the inclusion of the interband transitions leads to much stronger temperature-induced modulation of the imaginary part of the dielectric constant induced by the pump. We show that in the visible part of the spectrum a strong pump field can even lead to the decrease in the extinction coefficient for the co- or contrapropagating probe wave.

Ultrafast spatiotemporal control of the femtosecond Bessel surface plasmon polariton by a chirped laser pulse

Nondiffracting Bessel surface plasmon polariton (SPP) beam, which has unique properties of non-divergence, self-healing and straight trajectory, is potential to the fields of on-chip interconnect circuits and near-field optical trapping. However, it remains a significant challenge to achieve the spatiotemporal manipulation of nondiffracting Bessel SPP pulse in nanometer spatial and femtosecond temporal scale. Here, we propose a novel method of ultrafast spatiotemporal control of Bessel SPP pulses at the nano-femtosecond spatial–temporal scale. This on-chip plasmonic device can achieve the wavelength-based manipulation of the Bessel SPP beam with a high extinction ratio. The Bessel SPP pulse that develops in the femtosecond time scale in this device is presented. Importantly, we also demonstrate a solution for ultrafast spatiotemporal control of Bessel SPP pulses on the femtosecond time scale by controlling the chirp of the incident ultrafast laser pulse. Additionally, a higher coupling efficiency of the Bessel SPP into the waveguide than that of a plane SPP is demonstrated. The sequential coupling to the dielectric waveguides with femtosecond interval of Bessel SPP pulses is also achieved. This work offers great promise in applications such as high-speed, highly integrated nanophotonic devices, on-chip interconnect circuits and ultrafast beam shaping.

Spatiotemporal Fourier transform with femtosecond pulses for on-chip devices

On-chip manipulation of the spatiotemporal characteristics of optical signals is important in the transmission and processing of information. However, the simultaneous modulation of on-chip optical pulses, both spatially at the nano-scale and temporally over ultra-fast intervals, is challenging. Here, we propose a spatiotemporal Fourier transform method for on-chip control of the propagation of femtosecond optical pulses and verify this method employing surface plasmon polariton (SPP) pulses on metal surface. An analytical model is built for the method and proved by numerical simulations. By varying space- and frequency-dependent parameters, we demonstrate that the traditional SPP focal spot may be bent into a ring shape, and that the direction of propagation of a curved SPP-Airy beam may be reversed at certain moments to create an S-shaped path. Compared with conventional spatial modulation of SPPs, this method offers potentially a variety of extraordinary effects in SPP modulation especially associated with the temporal domain, thereby providing a new platform for on-chip spatiotemporal manipulation of optical pulses with applications including ultrafast on-chip photonic information processing, ultrafast pulse/beam shaping, and optical computing.

Energy and Momentum Distribution of Surface Plasmon-Induced Hot Carriers Isolated via Spatiotemporal Separation

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 that 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 toward high excitation energies and small in-plane momenta, which suggests a fundamentally different mechanism of hot electron generation, as previously unknown for surface plasmons.

Spatiotemporal manipulation on focusing and propagation of surface plasmon polariton pulses.

Surface plasmon polariton (SPP) provides an important platform for the design of various nanophotonic devices. However, it is still a big challenge to achieve spatiotemporal manipulation of SPP under both spatially nanoscale and temporally ultrafast conditions. Here, we propose a method of spatiotemporal manipulation of SPP pulse in a plasmonic focusing structure illuminated by a dispersed femtosecond light. Based on dispersion effect of SPP pulse, we achieve the functions of dynamically controlled wavefront rotation in SPP focusing and redirection in SPP propagation within femtosecond range. The influences of structural parameters on the spatiotemporal properties of SPP pulse are numerically studied, and an analytical model is built to explain the results. The spatiotemporal coupling of modulated SPP pulses to dielectric waveguides is also investigated, demonstrating an ultrafast turning of propagation direction. This work has great potential in applications such as on-chip ultrafast photonic information processing, ultrafast beam shaping and attosecond pulse generation.

Reduction of graphene oxide by nanofocused ultrafast surface plasmon pulses

We used ultrafast surface plasmon polariton (SPP) pulses that were focused into several tens of nm at the apex of a tapered metal tip to induce photoreduction of graphene oxide (GO), and we successfully fabricated nano graphene stripes with a minimum width of ∼200 nm. GO was reduced using about 1010 shots of SPP pulse irradiation. We evaluated the GO reduction with selective in situ coherent anti-Stokes Raman scattering measurements using spectrally focused SPP pulses.

Measurement of propagation of ultrafast surface plasmon polariton pulses using dual-probe scanning near-field optical microscopy.

We report the construction of diagnostics for ultrafast surface plasmon polariton (SPP) pulses that evolve spatiotemporally in femtosecond and nanometer scales. We constructed two types of scanning near-field optical microscopes (SNOMs) and verified that the temporal waveform of ultrafast SPP pulses can be measured by combining spectral interferometry (SI). In the illumination-collection (I-C) mode SNOM, which uses a single fiber probe to excite samples and collect optical responses, a lock-in detection scheme using a lock-in camera detects SI fringes even for extremely weak signal light pulses. With this I-C SI-SNOM scheme, we measured the complex plasmon response functions of gold (Au) nanorods on Ge2Sb2Te5 thin film, both in the crystal and amorphous phases. For a dual-probe SNOM (DSNOM), a dual-band modulation technique was introduced to independently control the probe-sample and probe-probe distances. With the DSNOM and by employing femtosecond SPP pulse excitation, we successfully measured the temporal waveform of an ultrafast SPP pulse that is propagating on an Au thin layer.

Selective Coherent Anti-Stokes Raman Scattering Microscopy Employing Dual-Wavelength Nanofocused Ultrafast Plasmon Pulses.

Ultrafast surface plasmon polariton (SPP) nanofocusing on a plasmonic metal tapered tip with femtosecond laser pulses enables background-free localized excitation beyond the diffraction limit. We demonstrate simultaneous nanofocusing of ultrafast SPP pulses at 440 and 800 nm, which were coupled with a common diffraction grating structure fabricated on an aluminum (Al) tapered tip, to the tip apex with a radius of ∼35 nm. We achieved selective coherent anti-Stokes Raman scattering (CARS) microscopy that combined an 800 nm (ω) SPP pump pulse, which achieves selective vibrational excitation by spectral focusing, and a 440 nm (2ω) SPP probe pulse. Raman intensity of this novel 2ω-CARS increased by a factor of 3.96 at the G-band and 4.00 at the 2D-band compared with that with ω-CARS for the monolayer graphene. The 2ω-CARS imaging method was applied for imaging a multiwalled carbon nanotube at the D-, G-, and 2D-bands. This dual-wavelength nanofocusing will open up new nanoscale microspectroscopy and optical excitation at the tip apex, such as sum frequency mixing, two-photon excitation.

The method of surface plasmon-polariton pulses generation via cooperative effects in waveguide spaser

The problem of sub-picosecond plasmon-polariton pulse formation in metal/dielectric interface due to collective decay of excited quantum dots, placed in the dielectric layer near the metal surface, is considered. Theoretical approach to selection of semiconductor quantum dots and dielectric host medium to increase the energy transmission of quantum dot collective excitations into surface plasmon-polariton modes of waveguide spaser is developed.

Formation of sub-picosecond plasmon–polariton pulses via cooperative effects in a waveguide spaser

The formation of surface plasmon–polariton pulses excited in a waveguide spaser during the collective decay of quantum dot excitons distributed in a dielectric layer near a metallic surface is considered. The waveguide spaser’s physical parameters and regimes of generation suitable for the formation of sub-picosecond plasmon–polariton pulses are determined with allowance for dissipative effects in the considered system.

Direct Observation of Surface Plasmon Polariton Propagation and Interference by Time-Resolved Imaging in Normal-Incidence Two Photon Photoemission Microscopy

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 formation of a standing surface plasmon polariton wave is imaged in time and space. We demonstrate that using a normal incidence geometry in time-resolved photoemission microscopy provides great advantages for in-situ imaging of surface plasmon polaritons in arbitrary plasmonic structures. A simple 1D wave-simulation is used to confirm the experimental results.

The method of surface plasmon-polariton pulses generation via cooperative effects in a waveguide spaser

Cooperative effects arising under conditions of a 0-D model for a dense ensemble of semiconductor quantum dots located in a dielectric layer near a flat metal surface are considered. The threshold conditions of the effect are determined and the values of the complex refractive index of the dielectric are chosen, which make it possible to increase the efficiency of the formation of surface plasmon-polariton (SPP) pulses.

Nanofocusing of Ultrafast Surface Plasmon Polariton Pulses with a Gold-Tapered Tip and Applications to Nonlinear Nanoimaging

Nanofocusing of Ultrafast Surface Plasmon Polariton Pulses with a Gold-Tapered Tip and Applications to Nonlinear Nanoimaging

Plasmonic pulse shaping and velocity control via photoexcitation of electrons in a gold film.

We study the possibility of surface plasmon polariton (SPP) pulse shape, delay and duration manipulation on sub-picosecond timescales via a high intensity pump SPP pulse photoexciting electrons in a gold film. We present a theoretical model describing this process and show that the pump induces the phase modulation of the probe pulse leading to its compression by about 20% and the variation of the delay between two SPP pulses up to 15 fs for the incident fluence of the pump of 1.5 mJ∙cm⁻².

Surface plasmon-polariton solitons and cnoidal waves at the boundary of dielectric crystal and metal

The generation of surface plasmon–polariton (SPP) pulses on the first and second harmonics of a carrier wave is considered at the boundary of a uniaxial crystal and non-magnetic metal. The SPP pulses on the first and second harmonics can arise in the forms of bright and dark solitons, or as cnoidal waves, in accordance with the velocity synchronism of the SPP pulses. The variation of the interaction efficiency and the changes of forms of the SPP pulses due to the exact or non-exact synchronism of their velocities have been investigated. It is shown that the selection of pairs of the crystal and metal allows changes in the forms of the SPP pulses.

Femtosecond-pulse control in nonlinear plasmonic systems

The collision of the two surface plasmon polariton pulses at the interface between a metal and a dielectric with cubic nonlinearity is investigated. We reveal the possibility of the reflection of a weak signal surface plasmon from the strong pump plasmon pulse resulting in the time delay and spectral shift in the signal plasmon pulse. Using such an interaction, one can control the propagation dynamics of the signal pulse via the modulation of the intensity of the pump pulse.

Measurement of surface plasmon autocorrelation functions

In this paper we demonstrate the realization of an autocorrelator for the characterization of ultrashort surface plasmon polariton (SPP) pulses. A wedge shaped structure is used to continuously increase the time delay between two interfering SPPs. The autocorrelation signal is monitored by non-linear two-photon photoemission electron microscopy. The presented approach is applicable to other SPP sensitive detection schemes that provide only moderate spatial resolution and may therefore be of general interest in the field of ultrafast plasmonics.

Transformation of the surface plasmon-polariton pulse to bright and dark solitons at the first and second harmonics

We consider the linear and nonlinear models of generation of the surface plasmon-polaritons on the boundary of a nonmagnetic dielectric medium and a nonmagnetic metal. We show how the three-dimensional incident wave is transformed to fluxes of surface plasmon-polaritons at the first and second harmonics of the transverse magnetic mode. These ‘slow’ and ‘fast’ fluxes of the surface plasmon-polaritons are formed at the first and second harmonics when their interaction is weak. We demonstrate that an input surface plasmon-polariton pulse transforms to bright and dark solitons for a strong harmonic interaction.

Physical characteristics with SPP in the metallic nanowires structure

In this work, the terahertz (THz) electromotive force (EMF) of the surface plasmon (SP) electric field and field strength was investigated in its propagation direction. Based on the nanowires structure, we introduced physical models which were light wave energy of surface plasmon polariton (SPP) pulse and the variation of EMF changes in the active condition. Results of theory and verification showed SPP generated EMF with 10−2–10 V among wire radii of 5–30 nm; the electric field was up to 105–106 V/cm in the radius of 5 nm; the electric field intensity induced localization at λ=850 nm, and at the same time light intensity amplified 40 times. The characteristics which are femtosecond SPP pulse response and force-field amplifier in this work are significant for nonlinear spectroscopy research.