15 research outputs found
Mimicking Chiral Light-Matter Interaction
We demonstrate that electric-dipole scatterers can mimic chiral light-matter
interaction by generating far-field circular polarization upon scattering, even
though the optical chirality of the incident field as well as that of the
scattered light is zero. The presented effect originates from the fact that
electric-dipole scatterers respond selectively only to the incident electric
field, which eventually results in depolarization of the transmitted beam and
in generation of far-field circular polarization. To experimentally demonstrate
this effect we utilize a cylindrical vector beam with spiral polarization and a
spherical gold nanoparticle positioned on the optical axis -- the axis of
rotational symmetry of the system. Our experiment and a simple theoretical
model address the fundamentals of duality symmetry in optics and chiral
light-matter interactions, accentuating their richness and ubiquity yet in
highly symmetric configurations.Comment: 5 pages, 2 figure
Weak measurement of elliptical dipole moments by C point splitting
We investigate points of circular polarization in the far field of
elliptically polarized dipoles and establish a relation between the angular
position and helicity of these C points and the dipole moment. In the case of
highly eccentric dipoles, the C points of opposite handedness exhibit only a
small angular separation and occur in the low intensity region of the emission
pattern. In this regard, we introduce an optical weak measurement approach that
utilizes the transverse electric (azimuthal) and transverse magnetic (radial)
far-field polarization basis. Projecting the far field onto a spatially varying
post-selected polarization state reveals the angular separation and the
helicity of the C points. We demonstrate the applicability of this approach and
determine the elliptical dipole moment of a particle sitting on an interface by
measuring the C points in its far field.Comment: 5 pages, 4 figure
Orbital-to-Spin Angular Momentum Conversion Employing Local Helicity
Spin-orbit interactions in optics traditionally describe an influence of the
polarization degree of freedom of light on its spatial properties. The most
prominent example is the generation of a spin-dependent optical vortex upon
focusing or scattering of a circularly polarized plane-wave by a nanoparticle,
converting spin to orbital angular momentum of light. Here, we present a
mechanism of conversion of orbital-to-spin angular momentum of light upon
scattering of a linearly polarized vortex beam by a spherical silicon
nanoparticle. We show that focused linearly polarized Laguerre-Gaussian beams
of first order () exhibit an -dependent spatial
distribution of helicity density in the focal volume. By using a dipolar
scatterer the helicity density can be manipulated locally, while influencing
globally the spin and orbital angular momentum of the beam. Specifically, the
scattered light can be purely circularly polarized with the handedness
depending on the orbital angular momentum of the incident beam. We corroborate
our findings with theoretical calculations and an experimental demonstration.
Our work sheds new light on the global and local properties of helicity
conservation laws in electromagnetism.Comment: 8 pages, 6 figures, 1 tabl
Designing a Broadband Pump for High-Quality Micro-Lasers via Modified Net Radiation Method
High-quality micro-lasers are key ingredients in non-linear optics, communication, sensing and low-threshold solar-pumped lasers. However, such micro-lasers exhibit negligible absorption of free-space broadband pump light. Recently, this limitation was lifted by cascade energy transfer, in which the absorption and quality factor are modulated with wavelength, enabling non-resonant pumping of high-quality micro-lasers and solar-pumped laser to operate at record low solar concentration. Here, we present a generic theoretical framework for modeling the absorption, emission and energy transfer of incoherent radiation between cascade sensitizer and laser gain media. Our model is based on linear equations of the modified net radiation method and is therefore robust, fast converging and has low complexity. We apply this formalism to compute the optimal parameters of low-threshold solar-pumped lasers. It is revealed that the interplay between the absorption and self-absorption of such lasers defines the optimal pump absorption below the maximal value, which is in contrast to conventional lasers for which full pump absorption is desired. Numerical results are compared to experimental data on a sensitized Nd[superscript 3+]:YAG cavity, and quantitative agreement with theoretical models is found. Our work modularizes the gain and sensitizing components and paves the way for the optimal design of broadband-pumped high-quality micro-lasers and efficient solar-pumped lasers.Russell Berrie Nanotechnology InstituteTechnion, Israel Institute of Technology. Grand Technion Energy ProgramIsrael Strategic Alternative Energy Foundatio
Huygens' Dipole for Polarization-Controlled Nanoscale Light Routing
Structured illumination allows for satisfying the first Kerker condition of
in-phase perpendicular electric and magnetic dipole moments in any isotropic
scatterer that supports electric and magnetic dipolar resonances. The induced
Huygens' dipole may be utilized for unidirectional coupling to waveguide modes
that propagate transverse to the excitation beam. We study two configurations
of a Huygens' dipole -- longitudinal electric and transverse magnetic dipole
moments or vice versa. We experimentally show that only the radially polarized
emission of the first and azimuthally polarized emission of the second
configuration are directional in the far-field. This polarization selectivity
implies that directional excitation of either TM or TE waveguide modes is
possible. Applying this concept to a single nanoantenna excited with structured
light, we are able to experimentally achieve scattering directivities of around
23 dB and 18 dB in TM and TE modes, respectively. This strong directivity paves
the way for tunable polarization-controlled nanoscale light routing and
applications in optical metrology, localization microscopy and on-chip optical
devices.Comment: 5pages, 2 figure