206 research outputs found
Weak Measurements of Light Chirality with a Plasmonic Slit
We examine, both experimentally and theoretically, an interaction of tightly
focused polarized light with a slit on a metal surface supporting
plasmon-polariton modes. Remarkably, this simple system can be highly sensitive
to the polarization of the incident light and offers a perfect
quantum-weak-measurement tool with a built-in post-selection in the
plasmon-polariton mode. We observe the plasmonic spin Hall effect in both
coordinate and momentum spaces which is interpreted as weak measurements of the
helicity of light with real and imaginary weak values determined by the input
polarization. Our experiment combines advantages of (i) quantum weak
measurements, (ii) near-field plasmonic systems, and (iii) high-numerical
aperture microscopy in employing spin-orbit interaction of light and probing
light chirality.Comment: 5 pages, 3 figure
Anomalous time delays and quantum weak measurements in optical micro-resonators
We study inelastic resonant scattering of a Gaussian wave packet with the
parameters close to a zero of the complex scattering coefficient. We
demonstrate, both theoretically and experimentally, that such near-zero
scattering can result in anomalously-large time delays and frequency shifts of
the scattered wave packet. Furthermore, we reveal a close analogy of these
anomalous shifts with the spatial and angular Goos-H\"anchen optical beam
shifts, which are amplified via quantum weak measurements. However, in contrast
to other beam-shift and weak-measurement systems, we deal with a
one-dimensional scalar wave without any intrinsic degrees of freedom. It is the
non-Hermitian nature of the system that produces its rich and non-trivial
behaviour. Our results are generic for any scattering problem, either quantum
or classical. As an example, we consider the transmission of an optical pulse
through a nano-fiber with a side-coupled toroidal micro-resonator. The zero of
the transmission coefficient corresponds to the critical coupling conditions.
Experimental measurements of the time delays near the critical-coupling
parameters verify our weak-measurement theory and demonstrate amplification of
the time delay from the typical inverse resonator linewidth scale to the pulse
duration scale.Comment: 14 pages, 5 figure
Acoustic Radiation Force and Torque on Small Particles as Measures of the Canonical Momentum and Spin Densities
We examine acoustic radiation force and torque on a small (subwavelength)
absorbing isotropic particle immersed in a monochromatic (but generally
inhomogeneous) sound-wave field. We show that by introducing the monopole and
dipole polarizabilities of the particle, the problem can be treated in a way
similar to the well-studied optical forces and torques on dipole Rayleigh
particles. We derive simple analytical expressions for the acoustic force
(including both the gradient and scattering forces) and torque. Importantly,
these expressions reveal intimate relations to the fundamental field properties
introduced recently for acoustic fields: the canonical momentum and spin
angular momentum densities. We compare our analytical results with previous
calculations and exact numerical simulations. We also consider an important
example of a particle in an evanescent acoustic wave, which exhibits the
mutually-orthogonal scattering (radiation-pressure) force, gradient force, and
torque from the transverse spin of the field.Comment: 7 pages, 3 figures, Supplemental Material, to appear in Phys. Rev.
Let
Electric current induced unidirectional propagation of surface plasmon-polaritons
Nonreciprocity and one-way propagation of optical signals is crucial for
modern nanophotonic technology, and is typically achieved using magneto-optical
effects requiring large magnetic biases. Here we suggest a fundamentally novel
approach to achieve unidirectional propagation of surface plasmon-polaritons
(SPPs) at metal-dielectric interfaces. We employ a direct electric current in
metals, which produces a Doppler frequency shift of SPPs due to the uniform
drift of electrons. This tilts the SPP dispersion, enabling one-way
propagation, as well as zero and negative group velocities. The results are
demonstrated for planar interfaces and cylindrical nanowire waveguides.Comment: 4 pages, 4 figures, to appear in Opt. Let
Angular Momenta and Spin-Orbit Interaction of Nonparaxial Light in Free Space
We give an exact self-consistent operator description of the spin and orbital
angular momenta, position, and spin-orbit interactions of nonparaxial light in
free space. Both quantum-operator formalism and classical energy-flow approach
are presented. We apply the general theory to symmetric and asymmetric Bessel
beams exhibiting spin- and orbital-dependent intensity profiles. The exact wave
solutions are clearly interpreted in terms of the Berry phases, quantization of
caustics, and Hall effects of light, which can be readily observed
experimentally.Comment: 8 pages, 3 figure
Spin-Hall effect and circular birefringence of a uniaxial crystal plate
The linear birefringence of uniaxial crystal plates is known since the 17th
century, and it is widely used in numerous optical setups and devices. Here we
demonstrate, both theoretically and experimentally, a fine lateral circular
birefringence of such crystal plates. This effect is a novel example of the
spin-Hall effect of light, i.e., a transverse spin-dependent shift of the
paraxial light beam transmitted through the plate. The well-known linear
birefringence and the new circular birefringence form an interesting analogy
with the Goos-H\"anchen and Imbert-Fedorov beam shifts that appear in the light
reflection at a dielectric interface. We report the experimental observation of
the effect in a remarkably simple system of a tilted half-wave plate and
polarizers using polarimetric and quantum-weak-measurement techniques for the
beam-shift measurements. In view of great recent interest in spin-orbit
interaction phenomena, our results could find applications in modern
polarization optics and nano-photonics.Comment: 16 pages, 8 figures, to appear in Optic
X-band microwave generation caused by plasma-sheath instability
It is well known that oscillations at the electron plasma frequency may
appear due to instability of the plasma sheath near a positively biased
electrode immersed in plasma. This instability is caused by transit-time
effects when electrons, collected by this electrode, pass through the sheath.
Such oscillations appear as low-power short spikes due to additional ionization
of a neutral gas in the electrode vicinity. Herein we present first results
obtained when the additional ionization was eliminated. We succeeded to prolong
the oscillations during the whole time a positive bias was applied to the
electrode. These oscillations could be obtained at much higher frequency than
previously reported (tens of GHz compared to few hundreds of MHz) and power of
tens of mW. These results in combination with presented theoretical estimations
may be useful, e.g., for plasma diagnostics.Comment: 12 pages, 7 figure
Angular momenta, helicity, and other properties of dielectric-fiber and metallic-wire modes
Spin and orbital angular momenta (AM) of light are well studied for
free-space electromagnetic fields, even nonparaxial. One of the important
applications of these concepts is the information transfer using AM modes,
often via optical fibers and other guiding systems. However, the
self-consistent description of the spin and orbital AM of light in optical
media (including dispersive and metallic cases) was provided only recently
[K.Y. Bliokh et al., Phys. Rev. Lett. 119, 073901 (2017)]. Here we present the
first accurate calculations, both analytical and numerical, of the spin and
orbital AM, as well as the helicity and other properties, for the full-vector
eigenmodes of cylindrical dielectric and metallic (nanowire) waveguides. We
find remarkable fundamental relations, such as the quantization of the
canonical total AM of cylindrical guided modes in the general nonparaxial case.
This quantization, as well as the noninteger values of the spin and orbital AM,
are determined by the generalized geometric and dynamical phases in the mode
fields. Moreover, we show that the spin AM of metallic-wire modes is
determined, in the geometrical-optics approximation, by the transverse spin of
surface plasmon-polaritons propagating along helical trajectories on the wire
surface. Our work provides a solid platform for future studies and applications
of the AM and helicity properties of guided optical and plasmonic waves.Comment: 12 pages, 4 figures, to appear in Optic
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