9 research outputs found
Experimental realization of Lorentz boosts of space-time wave packets
It is now well-understood that a Lorentz boost of a spatially coherent
monochromatic optical beam yields a so-called space-time wave packet (STWP): a
propagation-invariant pulsed beam whose group velocity is determined by the
relative velocity between the source and observer. Moreover, the Lorentz boost
of an STWP is another STWP, whose group velocities are related by the
relativistic law for addition of velocities typically associated with massive
particles. We present an experimental procedure for testing this prediction in
both the subluminal and superluminal regimes that makes use of spatio-temporal
Fourier synthesis via a spatial light modulator. Our approach enables realizing
the change in temporal bandwidth, the invariance of the spatial bandwidth, the
concomitant change in the spatio-temporal wave-packet envelope, and the change
in group velocity that all accompany a Lorentz boost of a monochromatic optical
beam. The only consequence of the Lorentz boost not captured by this
methodology is the Doppler shift in the optical carrier. This work may provide
an avenue for further table-top demonstration of relativistic transformations
of optical fields.Comment: 13 pages, 10 figure
Transverse spin angular momentum of space-time surface plasmon polariton wave packet
In addition to longitudinal spin angular momentum (SAM) along the axis of
propagation of light, spatially structured electromagnetic fields such as
evanescent waves and focused beams have recently been found to possess
transverse SAM in the direction perpendicular to the axis of propagation. In
particular, the SAM of SPPs with spatial structure has been extensively studied
in the last decade after it became clear that evanescent fields with spatially
structured energy flow generate threedimensional spin texture. Here we present
numerical calculations of the space-time surface plasmon polariton (ST-SPP)
wave packet, a plasmonic bullet that propagates at an arbitrary group velocity
while maintaining its spatial distribution. ST-SPP wave packets with complex
spatial structure and energy flow density distribution determined by the group
velocity are found to propagate with accompanying three-dimensional spin
texture and finite topological charge density. Furthermore, the spatial
distribution of the spin texture and topological charge density determined by
the spatial structure of the SPP is controllable, and the deformation
associated with propagation is negligible. ST-SPP wave packets, which can
stably transport customizable three-dimensional spin textures and topological
charge densities, can be excellent subjects of observation in studies of
spinphotonics and optical topological materials.Comment: 15 pages, 6 figure
Observation of ultrabroadband striped space-time surface plasmon polaritons
Because surface plasmon polaritons (SPPs) are surface waves characterized by
one free transverse dimension, the only monochromatic diffraction-free spatial
profiles for SPPs are cosine and Airy waves. Pulsed SPP wave packets have been
recently formulated that are propagation-invariant and localized in the
in-plane dimensions by virtue of a tight spectral association between their
spatial and temporal frequencies, which have thus been dubbed `space-time' (ST)
SPPs. Because of the spatio-temporal spectral structure unique to ST-SPPs, the
optimal launching strategy of such novel plasmonic field configurations remains
an open question. We present here a critical step towards realizing ST-SPPs by
reporting observations of ultrabroadband striped ST-SPPs. These are SPPs in
which each wavelength travels at a prescribed angle with respect to the
propagation axis to produce a periodic (striped) transverse spatial profile
that is diffraction-free. We start with a free-space ST wave packet that is
coupled to a ST-SPP at a gold-dielectric interface, and unambiguously identify
the ST-SPP via an axial beating detected in two-photon fluorescence produced by
the superposition of incident ST wave packet and the excited surface-bound
ST-SPP. These results highlight a viable approach for efficient and reliable
coupling to ST-SPPs, and thus represent the first crucial step towards
realization of the full potential of ST-SPPs for plasmonic sensing and imaging.Comment: 9 pages, 8 figure
Spectral tuning of SPP reflection by quasi-symmetric metal nano-block arrays
We investigate the spectral tuning of the SPP wave packets by quasi-symmetric arrays composed of metal blocks with two different structural lengths. The FDTD simulations showed a resonance phenomenon in the gap between the blocks when the two blocks have different lengths in the longitudinal direction. Furthermore, the resonance of the gap resulted in a significant spectral modulation of the reflected SPP wave that depended on the structural length and positional relationship of the blocks
Transverse spin angular momentum of space-time surface plasmon polariton wave packet
In addition to longitudinal spin angular momentum (SAM) along the axis of propagation of light, spatially structured electromagnetic fields such as evanescent waves and focused beams have recently been found to possess transverse SAM in the direction perpendicular to the axis of propagation. In particular, the SAM of SPPs with spatial structure has been extensively studied in the last decade after it became clear that evanescent fields with spatially structured energy flow generate threedimensional spin texture. Here we present numerical calculations of the space-time surface plasmon polariton (ST-SPP) wave packet, a plasmonic bullet that propagates at an arbitrary group velocity while maintaining its spatial distribution. ST-SPP wave packets with complex spatial structure and energy flow density distribution determined by the group velocity are found to propagate with accompanying three-dimensional spin texture and finite topological charge density. Furthermore, the spatial distribution of the spin texture and topological charge density determined by the spatial structure of the SPP is controllable, and the deformation associated with propagation is negligible. ST-SPP wave packets, which can stably transport customizable three-dimensional spin textures and topological charge densities, can be excellent subjects of observation in studies of spinphotonics and optical topological materials