arXiv subjects

Thierry Grosjean

Publications and source records attributed to Thierry Grosjean.

18 recordsLinked to original sources

arXiv2025

Tunable magnon emission from a nano-optomagnet

The growing demand for dense, energy-efficient, and high-frequency signal processing continues to drive device miniaturization. While downscaling remains a central challenge, magnons offer a promising solution as nanoscale signal carriers, supporting broadband operation from GHz to THz without moving charge carriers and generating Joule heating. However, their integration at the nanoscale is limited by conventional electrical excitation based on coplanar waveguides, which require metal pads few to hundreds of micrometres in size. Here, we demonstrate tunable magnon emission into a yttrium iron garnet film by focusing microwave-modulated laser light onto an integrated Au nanodisc. Using inelastic light scattering spectroscopy, we observe magnons whose frequencies match the optical modulation frequencies in the GHz frequency regime. The largest magnon amplitudes are found for circularly polarized laser light and specific nanodisc diameters consistent with a plasmon-enhanced inverse Faraday effect. These results establish plasmonic nanoantennas as reconfigurable nanoscale magnon sources, enabling broadband signal generation governed entirely by optical modulation.

physics.optics↗

arXiv2025

Seven-Probe Fiber Detector for Time-Resolved Source Tracking in HDR-Brachytherapy: Experimental Evaluation

{\bf Purpose:} This study evaluates a compact biocompatible Seven-probe Scintillator Detector (7SD) for monitoring HDR-BT treatment sequences across a range of dwell times and source-probe spacings representative of most HDR-BT techniques. {\bf Methods:} The SSD comprises seven detection cells made of Gd$_2$O$_2$S:Tb, each measuring 0.28 $\pm$ 0.02 mm in diameter and 0.43 $\pm$ 0.02 mm in length, coupled to the microstructured tips of silica optical fibers (110-micron diameter). The probes, spaced 15 mm apart along the fiber axis, are organized into a bundle with a total diameter of less than 0.45 mm. The SSD was tested using a MicroSelectron 9.1 Ci Ir-192 HDR afterloader connected to a BT stainless steel interstitial needle. Detection signals were acquired with an sCMOS camera equipped. Monitoring of dwell times and positions was performed by combining detection signals from all seven probes. {\bf Results:} A total of 4,040 dwell positions were analyzed, covering source-probe spacings from 10 to 36 mm and a source travel range of 62 mm, with dwell times ranging from 0.1 to 19.5 s. The 7SD successfully identified 99.5\% of the dwell positions. In cylindrical coordinates, the measured dwell positions deviated from the planned values by 0.224 $\pm$ 0.155 mm (radial) and 0.077 $\pm$ 0.181 mm (axial, source travel axis). The average deviation from planned dwell times was 0.006 $\pm$ 0.061 s. 99.4\% of the dwell positions were measured within the 1 mm reliability threshold. The remaining 0.6\% of deviations consistently occurred at the initial dwell position of treatment sequences and appear to stem from a systematic source positioning error by the afterloader. Additionally, the detector accurately identified intentional needle mispositioning scenarios with sub-millimeter accuracy.

physics.med-ph↗

arXiv2024

Optomagnetism with plasmonic skyrmion

Research at the frontier between optics and magnetism is revealing a wealth of innovative phenomena and avenues of exploration. Optical waves are demonstrating the capacity to induce ultrafast magnetism, while optical analogs of magnetic states, such as magnetic skyrmions, offer the prospect of novel spin-optical states. In this paper, we strengthen the synergy between light and magnetism by exploring the ability of plasmonic Neel skyrmions to create a stationary magnetic field within a thin gold film. We show that, when generated using a focused radially-polarized vortex beam, a plasmonic Neel skyrmion emerges as an optimum for inducing optomagnetism in a thin gold film. Optical skyrmions offer new degrees of freedom for enhancing and controlling optomagnetism in plasmonic nanostructures, with direct application in all-optical magnetization switching, magnetic recording, and the excitation of spin waves.

physics.optics↗

arXiv2023

Optical spin waves

Chirality is inherent to a broad range of systems, including in solid-state and wave physics. The precession (chiral motion) of electron spins in magnetic materials, forming spin waves, has various properties and many applications in magnetism and spintronics. We show that an optical analog of spin waves can be generated in arrays of plasmonic nanohelices. Such optical waves arise from the interaction between chiral helix eigenmodes carrying spin angular momentum. We demonstrate that these optical spin waves are reflected at the interface between successive domains of enantiomeric nanohelices, forming a heterochiral lattice, regardless of the wave propagation direction within the lattice. Optical spin waves may be applied in techniques involving photon spin, ranging from data processing and storage to quantum optics.

physics.optics↗

arXiv2023

Seven-probe scintillator dosimeter for treatment verification in HDR-brachytherapy

Purpose: We introduce a novel concept of a compact multiprobe scintillator detector and demonstrate its applicability in HDR-brachytherapy. Our fabricated seven-probe system is sufficiently narrow to be inserted in a brachytherapy needle or in a catheter. Methods: Our multiprobe detection system results from the parallel implementation of a miniaturized scintillator detector at the end of a bundle of seven fibers. The resulting system, which is narrower than 320 microns, is tested with a MicroSelectron 9.1 Ci Ir-192 HDR afterloader, in a water phantom. The detection signals from all seven probes are simultaneously read with an sCMOS camera (at a rate of 0.06 s). The camera is coupled to a chromatic filter to cancel Cerenkov signal induced within the fibers upon exposure. By implementing an aperiodic array of six scintillating cells along the bundle axis (one probe is kept bare to assess the stem effect), we first determine the range of inter-probe spacings leading to optimal source tracking accuracy. Then, three different source tracking algorithms involving sequentially or simultaneously all the scintillating probes are tested and compared. In each case, dwell positions are assessed from dose measurements and compared to the treatment plan. Dwell time is also determined and compared to the treatment plan. Results: The optimum inter-probe spacing for an accurate source tracking ranges from 15 mm to 35 mm. The optimum detection algorithm consists of adding the readout signals from all detector probes. In that case, the error to the planned dwell positions is of 0.01+/-0.14 mm and 0.02+/-0.29 mm at spacings between the source and detector axes of 5.5 and 40 mm, respectively. Using this approach, the average deviations to the expected dwell time are of -0.006+/-0.009 s and -0.008+/-0.058 s, at spacings between source and probe axes of 5.5 mm and 20 mm, respectively.

physics.ins-det↗

arXiv2021

Inverse-Faraday effect from the orbital angular momentum of light

It is usually admitted that the inverse Faraday effect (IFE) originates from the spin angular momentum (SAM) of light. In this paper, we evidence that part of the IFE in a metal is induced by the orbital angular momentum (OAM) of light. On the basis of a hydrodynamic model of the conduction electron gas, we describe the dependence of the IFE on the spin and orbital angular momenta as well as spin-orbit interaction in a non-paraxial light beam. We also numerically quantify the relative contributions of the SAM and OAM of light to the IFE in a thin gold film illuminated by different focused beams carrying SAM and/or OAM. The OAM of light provides a new degree of freedom in the control of the IFE and resulting optomagnetic field, thus potentially impacting various research fields including all-optical magnetization switching and spin-wave excitation.

physics.optics↗

arXiv2020

Optomagnets in nonmagnetic plasmonic nanostructures

Using a hydrodynamic model of the free electron gas of metal, we theoretically investigate optically-induced DC current loops in a plasmonic nanostructure. Such current loops originate from an optical rectification process relying on three electromotive forces, one of which arises from an optical spin-orbit interaction. The resulting static magnetic field is found to be maximum and dramatically confined at the corners of the plasmonic nanostructure, which reveals the ability of metallic discontinuities to concentrate and tailor static magnetic fields on the nanoscale.

physics.optics↗

arXiv2019

Miniaturized fiber dosimeter of medical radiations on a narrow optical fiber

Fiber dosimeters have recently drawn much interest for measuring in vivo and in real time the dose of medical radiations. This paper presents the first miniaturized fiber dosimeter integrated at the end of a narrow 125-micron outer diameter optical fiber. Miniaturization is rendered possible by exploiting the concept of a leaky wave optical antenna for interfacing the scintillators and the fiber, and by taking advantage of the low propagation loss of narrow silica fibers and high detection yield of single-pixel photon counters. Upon irradiation at 6 MV, our fiber probe led to a linear detection response with a signal-to-noise ratio as high as 190 in air. Although implemented with inorganic scintillators and fiber, our fiber probe induces an intensity contrast in the impinging radiation lower than 0.9% over an area of 0.153 mm2. Our nano-optically driven approach opens the route for ultra-compact fiber dosimeters of negligible footprint in the radiotherapeutic processes, even with non-water equivalent fibers and scintillators. A large panel of therapies relying on ionizing radiations (photons or charged particles) may take benefit of this nano-optically-driven technology.

physics.med-ph↗

arXiv2019

Individual plasmonic helix for probing light chirality

We investigate the plasmonic nanohelix as an individual subwavelength element for locally probing light chirality. We show that an hybrid nanoantenna combining a carbon-gold core-shell helix and a plasmonic nanoaperture transmits circularly polarized light with the same handedness as the helix and blocks the other. Such an assymmetric response is spatially localized, spectrally broadband and background-free. Finally, we demonstrate the possibility to engineer an individual plasmonic helix at the apex of a sharp tip typically used in scanning near-field microscopies, thus opening the prospect of moveable local probes for high resolution sensing and mapping of light chirality and chiroptical forces

physics.optics↗

arXiv2018

Bloch surface waves at the telecommunication wavelength with Lithium Niobate as top layer for integrated optics

Lithium niobate (LN) based devices are widely used in integrated and nonlinear optics. This material is robust and resistive to high temperatures, which makes the LN-based devices table, but challenging to fabricate. In this work we report on the design, manufacturing and characterization of engineered dielectric media with thin film lithium niobate (TFLN) on top for the coupling and propagation of electromagnetic surface waves at the telecommunication wavelengths. The designed one-dimentional photonic crystal (1DPhC) sustains Bloch surface waves at the multilayer/air interface at 1550 nm wavelength with a propagation detected over a distance of 3 mm. The working wavelength and improved BSW propagation parameters open the way for exploration of nonlinear properties of BSW based devices. It is also expected that these novel devices will modify BSW propagation and coupling by external thermal/electrical stimuli due to the improved quality of the TFLN top layer of 1DPhC.

physics.optics↗

arXiv2017

Magnetic spin-orbit interaction directs Bloch surface waves

We study the directional excitation of optical surface waves controlled by the magnetic field of light. We theoretically predict that a spinning magnetic dipole develops a tunable unidirectional coupling of light to TE-polarized Bloch surface waves (BSWs). Experimentally, we show that the helicity of light projected onto a subwavelength groove milled in the top layer of a 1D photonic crystal (PC) controls the power distribution between two TE-polarized BSWs excited on both sides of the groove. Such a phenomenon is shown to be mediated solely by the helicity of the magnetic field of light, thus revealing a magnetic spin-orbit interaction. Remarkably, this magnetic optical effect is clearly observed with a near-field coupler governed by an electric dipole moment: it is of the same order of magnitude as the electric optical effects involved in the coupling. The magnetic spin-orbit interaction opens new degrees of freedom in the manipulation of light and offers appealing novel opportunities in the development of integrated optical functionalities.

physics.optics↗

arXiv2016

Doubly resonant photonic antenna for single infrared quantum dot imaging at telecommunication wavelengths

Colloidal Quantum dots (CQDs) are nowadays one of the cornerstones of modern photonics as they have led to the emergence of new optoelectronic and biomedical technologies. However, the full characterization of these quantum emitters is currently restricted to the visible wavelengths and it remains a key challenge to optically probe single CQDs operating in the infrared spectral domain which is targeted by a growing number of applications. Here, we report the first experimental detection and imaging at room temperature of single infrared CQDs operating at telecommunication wavelengths. Imaging was done with a doubly resonant bowtie nano-aperture antenna (BNA) written at the end of a fiber nanoprobe, whose resonances spectrally fit the CQD absorption and emission wavelengths. Direct near-field characterization of PbS CQDs reveal individual nanocrystals with a spatial resolution of 75 nm (lambda/20) together with their intrinsic 2D dipolar free-space emission properties and exciton dynamics (blinking phenomenon). Because the doubly resonant BNA is strongly transmissive at both the CQD absorption and emission wavelengths, we are able to perform all-fiber nano-imaging with a standard 20 % efficiency InGaAs avalanche photodiode (APD). Detection efficiency is predicted to be 3000 fold larger than with a conventional circular aperture tip of the same transmission area. Double resonance BNA fiber probes thus offer the possibility of exploring extreme light-matter interaction in low band gap CQDs with current plug-and-play detection techniques, opening up new avenues in the fields of infrared light emitting devices, photodetectors, telecommunications, bio-imaging and quantum information technology.

physics.optics↗

arXiv2016

Ultracompact fiber integrated X-ray dosimeter based on scintillators coupled to a nano-optical antenna

High energy radiations are nowadays cornerstone in scientific, medical and industrial imaging and cancer therapy. However, their detection and dosimetry are restricted to systems of modest compactness that are not compatible with endoscopy. Here, we report the first experimental imaging and dosimetry of X-rays with an ultracompact sensor integrated at the end of a single mode optical fiber (125 $μ$m full diameter). We realize such a dosimeter by coupling luminescent scintillators to a nano-optical antenna engineered at the end of the fiber and by detecting in-fiber outcoupled luminescence with a photon counter. Direct profile and real-time dosimetry of a X-ray focused beam reveals a spatial resolution of a few microns together with a sensitivity better than 10$^3$ X-photons$/$s$/μ$m$^2$ at energies of 8-10 keV. Because the nano-optical platform is auto-aligned with respect to the fiber, the resulting dosimeter is plug-and-play, flexible, and it is suitable for ultralow footprint endoscopic investigations at higher X-ray energies. Our nano-optical approach thus offers the possibility of X-ray profiling and dosimetry in ultra-confined environments, opening up new avenues in the fields of X-ray imaging, real-time control of cancer radiotherapies and Curie therapies, medical and industrial endoscopy, etc. With this study, nano-optical antennas make a first key contribution to the development of X-ray sensing protocols and architectures.

physics.optics↗

arXiv2016

On the Coupling of Photon Spin to Electron Orbital Angular Momentum

Partially gold coated 90 degree glass wedges and a semi - infinite slit in a thin film of gold ending in a conducting nano-junction serve as samples to investigate the transfer of photon spin to electron orbital angular momentum. These structures were specifically designed as samples where an incident beam of light is retroreflected. Since in the process of retroreflection the turning sense of a circularly polarized beam of light does not change and the direction of propagation is inverted, the photon spin is inverted. Due to conservation of angular momentum a transfer of photon spin to electron orbital angular momentum of conduction electrons occurs. In the structures a circular movement of electrons is blocked and therefore the transfered spin can be detected as a photovoltage due to an electromotive force which is induced by the transfer of angular momentum. Depending on the polarization of the incident beam, a maximum photovoltage of about 0,2 micro V was measured for both structures. The results are interpreted in terms of a classical electrodynamic model of the monochromatic linearly polarized photon as a propagating solitary electromagnetic wave of finite energy hf which carries an angular momentum h/2pi which is elaborated elsewhere where h is Plancks constant and f the frequency of light. The relative values of the measured photovoltages for different polarizations can well be explained by the electrodynamic model of a photon and an associated spin angular momentum. The absolute values of the measured photovoltages are also consistent with the interpretation. The observed effects are closely related to the lateral Fedorov Imbert shift of focused beams in optics and the optical spin Hall effect and to other non linear optical effects such as the inverse faraday effect for which a new interpretation is given here in terms of the electrodynamic model of the photon and its spin.

physics.gen-ph↗

arXiv2015

Unidirectional sub-diffraction waveguiding based on optical spin-orbit coupling in subwavelength plasmonic waveguides

Subwavelength plasmonic waveguides show the unique ability of strongly localizing (down to the nanoscale) and guiding light. These structures are intrinsically two-way optical communication channels, providing two opposite light propagation directions. As a consequence, when light is coupled to these planar integrated devices directly from the top (or bottom) surface using strongly focused beams, it is equally shared into the two opposite propagation directions. Here, we show that symmetry can be broken by using incident circularly polarized light, on the basis of a spin-orbital angular momentum transfer directly within waveguide bends. We predict that up to 94 \% of the incoupled light is directed into a single propagation channel of a gap plasmon waveguide. Unidirectional propagation of strongly localized optical energy, far beyond the diffraction limit, becomes switchable by polarization, with no need of intermediate nano-antennas/scatterers as light directors. This study may open new perspectives in a large panel of scientific domains, such as nanophotonic circuitry, routing and sorting, optical nanosensing, nano-optical trapping and manipulation.

physics.optics↗

arXiv2015

Resonant bowtie aperture nano-antenna for the control of optical nanocavities resonance

Scanning Near-field Optical Microscopy (SNOM) has been successful in finely tuning the optical properties of photonic crystal (PC) nanocavities. The SNOM nanoprobes proposed so far allowed for either redshifting or blueshifting the resonance peak of the PC structures. In this Letter, we theoretically demonstrate the possibility of redshifting (up to +0.65nm) and blueshifting (up to $-5$~nm) PC cavity resonance with a single SNOM probe. This probe is obtained by opening a bowtie-aperture nano-antenna (BNA) at the apex of a metal-coated tip. This double-way PC tunability is the result of a competition between the effects of the BNA resonance (induced electric dipole leading to a redshift) and the metal-coated tip (induced magnetic dipole giving rise to a blueshift) onto the PC mode volume. The sign of the spectral shift is modified by simply controlling the tip-to-PC distance. This study opens the way to the full postproduction control of the resonance wavelength of high quality factor optical cavities.

physics.optics↗

arXiv2015

Remote optical sensing on the nanometer scale with a bowtie aperture nano-antenna on a SNOM fiber tip

Plasmonic nano-antennas have proven the outstanding ability of sensing chemical and physical processes down to the nano-meter scale. Sensing is usually achieved within the highly confined optical fields generated resonantly by the nano-antennas, i.e. in contact to the nano-structures. In these paper, We demonstrate the sensing capability of nano-antennas to their larger scale environment, well beyond their plasmonic confinement volume, leading to the concept of 'remote' (non contact) sensing on the nano-meter scale. On the basis of a bowtie-aperture nano-antenna (BNA) integrated at the apex of a SNOM fiber tip, we introduce an ultra-compact, move-able and background-free optical nano-sensor for the remote sensing of a silicon surface (up to distance of 300 nm). Sensitivity of the BNA to its large scale environment is high enough to expect the monitoring and control of the spacing between the nano-antenna and a silicon surface with sub-nano-meter accuracy. This work paves the way towards a new class of nano-positionning technique, based on nano-antenna resonance monitoring, that are alternative to nano-mechanical and optical interference-based devices.

physics.optics↗

arXiv2009

Radially Polarized Conical Beam from an Embedded Etched Fiber

We propose a method for producing a conical beam based on the lateral refraction of the TM01 mode from a two-mode fiber after chemical etching of the cladding, and for controlling its radial polarization. The whole power of the guided mode is transferred to the refracted beam with low diffraction. Polarization control by a series of azimuthal detectors and a stress controller affords the transmission of a stabilized radial polarization through an optical fiber. A solid component usable for many applications has been obtained.

physics.optics↗