Counterpropagating Surface Plasmon Polaritons Research Articles

Self-induced decay of intense laser pulse into a pair of surface plasmons

We show theoretically that an intense femtosecond optical pulse incident normally on a metal surface tends to decay into a pair of counterpropagating surface plasmon polaritons (SPPs). The interference field heats the medium periodically, which causes a periodic permittivity perturbation and, in turn, resonantly amplifies the magnitudes of the SPPs. The instability growth time is 10--50 fs for typical metals at laser fluences of about $\ensuremath{\sim}1\phantom{\rule{0.16em}{0ex}}\mathrm{J}/{\mathrm{cm}}^{2}$, so this mechanism is important for understanding the dynamics of the optical pulse absorption under damaging conditions, and it is promising for the interpretation of laser-induced periodic surface structure formation in single- and few-pulse pumping regimes.

Ultrasensitive nanoplasmonic biosensor based on interferometric excitation of multipolar plasmonic modes.

We propose a nanoplasmonic interferometric biosensor, which exploits the selective excitation of multipolar plasmonic modes in a nanoslit to provide a novel scheme for highly-sensitive biosensing. In this design, two counter-propagating surface plasmon polaritons interfere at the location of the nanoslit, selectively exciting the dipolar and quadrupolar modes of the structure depending on the phase relationship induced by the analyte. The contrasting radiation patterns produced by these modes result in large changes in the angular distribution of the transmitted light that depends on the analyte concentration. The resultant far-field is numerically modeled and the sensing performance of the structure is assessed, resulting in maximum bulk and surface sensitivities of SB = 1.12 × 105 deg/RIU and SS = 302 deg/RIU, respectively, and a bulk-sensing resolution of the order of 10-8 RIU. The design allows ample control over the trade-off between operating range and resolution through the slit's width, making this platform suitable for a broad range of sensing requirements.

Surface plasmon polariton pulse shaping via two-dimensional Bragg grating pairs

Abstract We demonstrate control over the spatial and temporal properties of surface plasmon polaritons (SPPs) launched from nanohole arrays in silver. The arrays provide wave vector matching to allow the conversion of free-space photons into counter-propagating SPPs. SPPs launched from multiple arrays interfere at well-defined spatial positions, and the interference fringes form an all-SPP periodic nano-optical grating which evolves in space and time as the SPPs propagate. The spatio-temporal characteristics of the optical grating can be tuned through various nanohole array parameters such as tilt angle, separation, and array width. In addition, we examine multiperiodic arrays (MPAs) consisting of arrays with different pitches placed adjacent to one another. This platform allows the temporal interference of SPPs with different central wavelengths to be tailored through the MPA geometric and structural parameters. The temporal interference serves as an encoded signal, whereby the frequency components can be controlled by the array properties.

Shift of the surface plasmon polariton interference pattern in symmetrical arc slit structures and its application to Rayleigh metallic particle trapping.

In symmetric nano/micro metal slit structures, interference patterns are produced by counter-propagating surface plasmon polaritons (SPPs) in the the center of structures, which can be employed to improve the resolution of microscopy and surface etching and to realize particle trapping. This paper focuses on the shift of the SPP interference patterns in the symmetric arc slit structures. The excitation models with one incident beam and two incident beams are established and analyzed respectively, and methods to shift the SPP interference patterns via adjusting the tilt angle and initial phase of the excitation beams are compared. The FDTD simulation results show that these methods can precisely shift the SPP interference patterns in the symmetrical arc slits. Compared to the linear slits, the SPP waves arising from arc slits are more strongly focused, resulting in a stronger gradient force. The characteristics of stronger focus and dynamic shifting of the focal spot give the symmetric arc slit structure unique advantages in the capture and transfer of the Rayleigh metallic particle.

Interferometric control of plasmonic resonator based on polarization-sensitive excitation of surface plasmon polaritons.

A plasmonic resonator is proposed whose electromagnetic energy density can be tuned by the polarization state of the incident light. Counter-propagating surface plasmon polaritons, which are excited by polarization-sensitive subwavelength apertures, give tunability. Stored energy density in the resonator varies from the minimum to the maximum when the orientation angle of the incoming electric field rotates by 90 degrees. After optimizing a rectangular cavity and periodic gratings, the on/off ratio is calculated as 430 and measured as 1.55. Based on our scheme, interferometric control is executed simply by rotation of a polarizer. The proposed plasmonic resonator can be utilized in all-optically controlled active plasmonic devices, coherent network elements, particle trapping systems, and polarimeters.

Nanoscale imaging and spontaneous emission control with a single nano-positioned quantum dot

Plasmonic nanostructures confine light on the nanoscale, enabling ultra-compact optical devices that exhibit strong light-matter interactions. Quantum dots are ideal for probing plasmonic devices because of their nanoscopic size and desirable emission properties. However, probing with single quantum dots has remained challenging because their small size also makes them difficult to manipulate. Here we demonstrate the use of quantum dots as on-demand probes for imaging plasmonic nanostructures, as well as for realizing spontaneous emission control at the single emitter level with nanoscale spatial accuracy. A single quantum dot is positioned with microfluidic flow control to probe the local density of optical states of a silver nanowire, achieving 12 nm imaging accuracy. The high spatial accuracy of this scanning technique enables a new method for spontaneous emission control where interference of counter-propagating surface plasmon polaritons results in spatial oscillations of the quantum dot lifetime as it is positioned along the wire axis.

Surface-mediated four-wave mixing of nanostructures with counterpropagating surface plasmon polaritons

We demonstrate that four-wave mixing (FWM) signals from individual Si nanoparticles can be generated by the surface fields of traveling surface plasmon polariton modes. We have chosen a counterpropagating excitation scheme in which the nanoparticle is exposed only to surface excitation fields and not to direct laser illumination. We show that background-free, surface-mediated FWM of nanoparticles can be acquired, and that the resulting nonlinear radiation is coherent.

Scannable Plasmonic Trapping Using a Gold Stripe

Using counterpropagating surface plasmon polaritons (SPPs) on a gold stripe, we demonstrate a scannable integrated optical tweezer. We demonstrate the trapping of individual fluorescent beads on the stripe, which supports a single quasi-transverse magnetic (TM) mode at the metal-water interface. The beads are localized to the stripe center, with a standard deviation of 51 nm transverse to the stripe, corresponding to a trap stiffness of 1.7 pN/microm. The localization along the stripe is achieved by balancing the scattering forces from the two counterpropagating SPPs excited by prism coupling. The particle position along the stripe can be controlled by varying the relative intensity of the two input beams. This work adds an important new capability to plasmonic optical tweezers, that of scanning. We anticipate that this will broaden the range of applications of plasmonic optical manipulation.

Observations of backscattering effects in second-harmonic generation from a weakly rough metal surface

We present experimental observations of diffusely scattered second-harmonic light from a silver surface with weak random roughness. The roughness provides coupling of the incident wave to counterpropagating surface plasmon polaritons in the second harmonic. Rather than observing enhancement in the backscattering direction, a distinct minimum in the angular distribution is seen.

Surface plasmon polariton mechanism for enhanced backscattering of light from one-dimensional randomly rough metal surfaces

Recent experimental results of West and O’Donnell [ J. Opt. Soc. Am. A12, 390 ( 1995)] for the enhanced backscattering of p-polarized light from weakly rough, one-dimensional, random gold surfaces are compared with the predictions of two perturbative calculations of such scattering. The experimental surfaces were fabricated to possess power spectra that are nonzero in only a narrow range of wave numbers about the wave number of the surface plasmon polariton supported by them at the frequency of the incident light. As a consequence, enhanced backscattering that is due to the coherent interference of time-reversed scattering sequences involving counterpropagating surface plasmon polaritons is possible for only a limited range of values for the angles of incidence and scattering. The perturbative calculations used in the comparisons with experiment are the infinite-order calculation of McGurn et al. [ Phys. Rev. B31, 4866 ( 1985)] in the small-roughness approximation and the small-amplitude perturbation theory of Maradudin and Me′ndez [ Appl. Opt.32, 3335 ( 1993)] that is exact to fourth order in the surface-profile function. In both calculations the origin of enhanced backscattering is the coherent interference of multiply scattered surface plasmon polaritons with their time-reversed partners. The good quantitative and qualitative agreement between the theoretical and experimental results, with no fitting parameters, supports the conclusion of West and O’Donnell that their data demonstrate the existence of enhanced backscattering caused by the excitation of surface plasmon polaritons on a weakly rough random metal surface.

Scattering by plasmon polaritons on a rough surface with a periodic component

We investigate the scattering properties of a metal surface composed of the sum of a sinusoidal component and a one-dimensional Gaussian random process. In experimental work, such surfaces are produced in gold-coated photoresist by combining speckle-scanning methods with holographic grating fabrication techniques. In the diffusely scattered light, light bands and related effects that arise from the excitation of surface plasmon polaritons are observed; the angular position of the diffuse light bands corresponds to the positions of the resonant absorption anomalies of the unperturbed periodic surface. It is also shown that the measurements are closely consistent with the predictions of rigorous numerical methods based on the reduced Rayleigh equations, in which the diffuse scatter is determined through an average over an ensemble of rough surfaces. With an analytical theoretical method that treats the grating exactly and the roughness as a perturbation, it is shown that an observed enhancement of a diffuse light band in the backscattering configuration results from the coherent interference of scattering contributions from counterpropagating surface plasmon polaritons.