105 research outputs found
Evolutionary optimization of all-dielectric magnetic nanoantennas
Magnetic light and matter interactions are generally too weak to be detected,
studied and applied technologically. However, if one can increase the magnetic
power density of light by several orders of magnitude, the coupling between
magnetic light and matter could become of the same order of magnitude as the
coupling with its electric counterpart. For that purpose, photonic nanoantennas
have been proposed, and in particular dielectric nanostructures, to engineer
strong local magnetic field and therefore increase the probability of magnetic
interactions. Unfortunately, dielectric designs suffer from physical
limitations that confine the magnetic hot spot in the core of the material
itself, preventing experimental and technological implementations. Here, we
demonstrate that evolutionary algorithms can overcome such limitations by
designing new dielectric photonic nanoantennas, able to increase and extract
the optical magnetic field from high refractive index materials. We also
demonstrate that the magnetic power density in an evolutionary optimized
dielectric nanostructure can be increased by a factor 5 compared to state of
the art dielectric nanoantennas. In addition, we show that the fine details of
the nanostructure are not critical in reaching these aforementioned features,
as long as the general shape of the motif is maintained. This advocates for the
feasibility of nanofabricating the optimized antennas experimentally and their
subsequent application. By designing all dielectric magnetic antennas that
feature local magnetic hot-spots outside of high refractive index materials,
this work highlights the potential of evolutionary methods to fill the gap
between electric and magnetic light-matter interactions, opening up new
possibilities in many research fields.Comment: 13 pages, 4 figure
Optical horn antennas for efficiently transferring photons from a quantum emitter to a single-mode optical fiber
International audienceWe theoretically demonstrate highly efficient optical coupling between a single quantum emitter and a monomode optical fiber over remarkably broad spectral ranges by extending the concept of horn antenna to optics. The optical horn antenna directs the radiation from the emitter toward the optical fiber and efficiently phase-matches the photon emission with the fiber mode. Numerical results show that an optical horn antenna can funnel up to 85% of the radiation from a dipolar source within an emission cone semi-angle as small as 7 degrees (antenna directivity of 300). It is also shown that 50% of the emitted power from the dipolar source can be collected and coupled to an SMF-28 fiber mode over spectral ranges larger than 1000 nm, with a maximum energy transfer reaching 70 %. This approach may open new perspectives in quantum optics and sensing
An achiral magnetic photonic antenna as a tunable nanosource of superchiral light
Sensitivity to molecular chirality is crucial for many fields, from biology
and chemistry to the pharmaceutical industry. By generating superchiral light,
nanophotonics has brought innovative solutions to reduce the detection volume
and increase sensitivity at the cost of a non-selectivity of light chirality or
a strong contribution to the background. Here, we theoretically propose an
achiral plasmonic resonator, based on a rectangular nanoslit in a thin gold
layer behaving as a magnetic dipole, to generate a tunable nanosource of purely
superchiral light. This nanosource is free of any background, and the sign of
its chirality is externally tunable in wavelength and polarization. These
properties result from the coupling between the incident wave and the magnetic
dipolar character of our nano-antenna. Thus, our results propose a platform
with deep subwavelength detection volumes for chiral molecules in particular,
in the visible, and a roadmap for optimizing the signal-to-noise ratios in
circular dichroism measurements to reach single-molecule sensitivity
Broadband plasmonic nanoantennas for multi-color nanoscale dynamics in living cells
Recently, the implementation of plasmonic nanoantennas has opened new
possibilities to investigate the nanoscale dynamics of individual biomolecules
in living cell. However, studies have yet been restricted to single molecular
species as the narrow wavelength resonance of gold-based nanostructures
precludes the simultaneous interrogation of different fluorescently labeled
molecules. Here we exploited broadband aluminum-based nanoantennas carved at
the apex of near-field probes to resolve nanoscale-dynamic molecular
interactions on intact living cell membranes. Through multicolor excitation, we
simultaneously recorded fluorescence fluctuations of dual-color labeled
transmembrane receptors known to form nanoclusters in living cells.
Fluorescence cross-correlation studies revealed transient interactions between
individual receptors in regions of ~60 nm. Moreover, the high
signal-to-background ratio provided by the antenna illumination allowed us to
directly detect fluorescent bursts arising from the passage of individual
receptors underneath the antenna. Remarkably, by reducing the illumination
volume below the characteristic receptor nanocluster sizes, we resolved
molecular diffusion within nanoclusters and distinguished it from nanocluster
diffusion. Spatiotemporal characterization of transient interactions between
molecules is crucial to understand how they communicate with each other to
regulate cell function. Our work demonstrates the potential of broadband
photonic antennas to study multi-molecular events and interactions in living
cell membranes with unprecedented spatiotemporal resolution
Enhancing Magnetic Light Emission with All-Dielectric Optical Nanoantennas
Electric and magnetic optical fields carry the same amount of energy. Nevertheless, the efficiency with which matter interacts with electric optical fields is commonly accepted to be at least 4 orders of magnitude higher than with magnetic optical fields. Here, we experimentally demonstrate that properly designed photonic nanoantennas can selectively manipulate the magnetic versus electric emission of luminescent nanocrystals. In particular, we show selective enhancement of magnetic emission from trivalent europium-doped nanoparticles in the vicinity of a nanoantenna tailored to exhibit a magnetic resonance. Specifically, by controlling the spatial coupling between emitters and an individual nanoresonator located at the edge of a near field optical scanning tip, we record with nanoscale precision local distributions of both magnetic and electric radiative local densities of states (LDOS). The map of the radiative LDOS reveals the modification of both the magnetic and electric quantum environments induced by the presence of the nanoantenna. This manipulation and enhancement of magnetic light-matter interaction by means of nanoantennas opens up new possibilities for the research fields of opto-electronics, chiral optics, nonlinear&nano-optics, spintronics and metamaterials, amongst others.Peer ReviewedPostprint (author's final draft
Light funneling from a photonic crystal laser cavity to an optical nano-antenna: toward antenna-based laser nano-emission
International audienceWe show that the near-field coupling between a photonic crystal microlaser and a nanoantenna can enable hybrid photonic systems that are both physically compact and highly efficient at transferring optical energy into the nano-antenna. Up to 19.4% of the laser power from a micron-scale photonic crystal laser cavity is experimentally transferred to a bowtie aperture nano-antenna (BNA) whose area is 400-fold smaller than the overall emission area of the microlaser. Instead of a direct deposition of the nano-antenna onto the photonic crystal, it is fabricated at the apex of a fiber tip to be accurately placed in the near-field volume of the microlaser. Such light funneling within a hybrid structure provides a path for overcoming the diffraction limit in optical energy transfer to the nanoscale and should thus open promising avenues in the nanoscale enhancement and confinement of light in compact architectures, impacting applications such as biosensing, optical trapping, heating, spectroscopy, and nanoimaging
Enhancement and Inhibition of Spontaneous Photon Emission by Resonant Silicon Nanoantennas
Substituting noble metals for high-index dielectrics has recently been proposed as an alternative strategy in nanophotonics to design broadband optical resonators and circumvent the Ohmic losses of plasmonic materials. In this paper, we demonstrate that subwavelength silicon nanoantennas can manipulate the photon emission dynamics of fluorescent molecules. In practice, we show that dielectric nanoantennas can both increase and decrease the local density of optical states at room temperature, a process that is inaccessible with noble metals at the nanoscale. Using scanning probe microscopy, we analyze quantitatively, in three dimensions, the near-field interaction between a 100-nm fluorescent nanosphere and silicon nanoantennas with diameters ranging between 170 and 250 nm. Associated with numerical simulations, these measurements indicate increased or decreased total spontaneous decay rates by up to 15% and a gain in the collection efficiency of emitted photons by up to 85%. Our study demonstrates the potential of silicon-based nanoantennas for the low-loss manipulation of solid-state emitters at the nanoscale and at room temperature
Tip-enhanced near-field optical microscopy
Tip-enhanced near-field optical microscopy (TENOM) is a scanning probe technique capable of providing a broad range of spectroscopic information on single objects and structured surfaces at nanometer spatial resolution and with highest detection sensitivity. In this review, we first illustrate the physical principle of TENOM that utilizes the antenna function of a sharp probe to efficiently couple light to excitations on nanometer length scales. We then discuss the antenna-induced enhancement of different optical sample responses including Raman scattering, fluorescence, generation of photocurrent and electroluminescence. Different experimental realizations are presented and several recent examples that demonstrate the capabilities of the technique are reviewed
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