Revealing the subfemtosecond dynamics of orbital angular momentum in nanoplasmonic vortices

Abstract

The ability of light to carry and deliver orbital angular momentum (OAM) in the form of optical vortices has attracted much interest. The physical properties of light with a helical wavefront can be confined onto two-dimensional surfaces with subwavelength dimensions in the form of plasmonic vortices, opening avenues for thus far unknown light-matter interactions. Because of their extreme rotational velocity, the ultrafast dynamics of such vortices remained unexplored. Here we show the detailed spatiotemporal evolution of nanovortices using time-resolved two-photon photoemission electron microscopy. We observe both long- and short-range plasmonic vortices confined to deep subwavelength dimensions on the scale of 100 nanometers with nanometer spatial resolution and subfemtosecond time-step resolution. Finally, by measuring the angular velocity of the vortex, we directly extract the OAM magnitude of light.

Short-range surface plasmonics: Localized electron emission dynamics from a 60-nm spot on an atomically flat single-crystalline gold surface

“…Carving Archimedean spirals into the films ( 53 ) leads to angular orbital momentum of the short-range surface plasmons ( 54 ). It is natural to use tapered structures for adiabatic focusing of SR-SPPs.…”

Interaction of an Archimedean spiral structure with orbital angular momentum light

“…For the generation of vortices in planar systems, it can be shown that both the single spiral and the segmented spiral induce a similar phase relation if = d md [2]. However, due to the reduced curvature, the segmented spiral has reduced losses [8], hence we will also consider the segmented spiral here. Note that the number of segments m is also called topological charge of the spiral and is a geometrical property of the structure [2, 4-6, 8, 11, 24, 46].…”

“…For the grooved spiral in a metal system, it was found that a vortex of SPPs is generated, when the distance d between the parts of the segmented spiral agrees with the wavelength of the propagating SPP [2,7,8].…”

“…Recently it was shown that by grooving Archimedean spiral structures in a gold nano platelet, the surface plasmon polariton (SPP) field forms a vortex in the centre of the structure [1][2][3][4][5][6][7]. The femtosecond dynamics of the formation of the plasmonic vortex can be studied using time-resolved two-photon photoemission electron microscopy [8]. Such structures can be used as plasmonic lenses by focusing the light field to subwavelength dimensions [9][10][11][12].…”

Slit width oriented polarized wavefields transition involving plasmonic and photonic modes

“…Since the discovery of the extraordinary transmission [1], surface plasmon polaritons (SPPs) have provided a powerful tool for engineering nano-devices with various functionalities [2][3][4][5] and have given rise to interesting applications such as microscopy beyond diffraction limit [6,7], nanoscale focusing [3,4], compact plasmonic modulators [8] and hologram imaging [9]. In excitations and manipulations of plasmonic wavefields, metal nanoslit structures [10][11][12][13][14][15][16] and polarization states of the incident light [17][18][19] play important roles. The shape, width and orientation of slits are elements influencing the launched wavelets [17][18][19][20], and the interferences of the wavelets contribute to formations of the wavefield patterns [10][11][12][13][14], which can be described by the Huygens-Fresnel principle [21][22][23].…”