Optomagnetism with a 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, to the best of our knowledge, spin-optical states. In this Letter, we strengthen the synergy between light and magnetism by exploring the ability of plasmonic Neel skyrmions to create an optomagnetic field, i.e., an opto-induced stationary magnetic field, within a thin gold film. We show that, when generated using a focused radially polarized vortex beam (RPVB), 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.

Optical Spin Waves.

Chirality is inherent to a broad range of systems, including solid-state and wave physics. The precession (chiral motion) of the magnetic moments in magnetic materials, forming spin waves, has various properties and many applications in magnetism and spintronics. We show that an optical analogue of spin waves can be generated in arrays of plasmonic nanohelices. Such optical waves arise from the interaction between twisted helix eigenmodes carrying spin and orbital angular momenta. 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.

Six-probe scintillator dosimeter for treatment verification in HDR-brachytherapy.

BACKGROUND: In vivo dosimetry (IVD) is gaining interest for treatment delivery verification in HDR-brachytherapy. Time resolved methods, including source tracking, have the ability both to detect treatment errors in real time and to minimize experimental uncertainties. Multiprobe IVD architectures holds promise for simultaneous dose determinations at the targeted tumor and surrounding healthy tissues while enhancing measurement accuracy. However, most of the multiprobe dosimeters developed so far either suffer from compactness issues or rely on complex data post-treatment. PURPOSE: We introduce a novel concept of a compact multiprobe scintillator detector and demonstrate its applicability in HDR-brachytherapy. Our fabricated seven-fiber probing 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 six miniaturized inorganic Gd2 O2 S:Tb scintillator detectors at the end of a bundle of seven fibers, one fiber is kept bare to assess the stem effect. The resulting system, which is narrower than 320 microns, is tested with a MicroSelectron 9.14 Ci Ir-192 HDR afterloader, in a water phantom. The detection signals from all six probes are simultaneously read with a 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, we first determine the range of inter-probe spacings leading to optimal source tracking accuracy (first tracking method). Then, three different source tracking algorithms involving all the scintillating probes are tested and compared. In each of these four methods, 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 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 $-0.006\,\pm \,0.009$ s and - 0.008 ± 0.058 $-0.008\, \pm 0.058$ s, at spacings between source and probe axes of 5.5 and 20 mm, respectively. CONCLUSIONS: Our six-probe Gd2 O2 S:Tb dosimeter coupled to a sCMOS camera can perform time-resolved treatment verification in HDR brachytherapy. This detection system of high spatial and temporal resolutions (0.25 mm and 0.06 s, respectively) provides a precise information on the treatment delivery via a dwell time and position verification of unmatched accuracy.

Characterization of a miniaturized scintillator detector for time-resolved treatment monitoring in HDR-brachytherapy.

Purpose.HDR brachytherapy combines steep dose gradients in space and time, thereby requiring detectors of high spatial and temporal resolution to perform accurate treatment monitoring. We demonstrate a miniaturized fiber-integrated scintillator detector (MSD) of unmatched compactness which fulfills these conditions.Methods.The MSD consists of a 0.28 mm large and 0.43 mm long detection cell (Gd2O2S:Tb) coupled to a 110 micron outer diameter silica optical fiber. The fiber probe is tested in a phantom using a MicroSelectron 9.1 Ci Ir-192 HDR afterloader. The detection signal is acquired at a rate of 0.08 s with a standard sCMOS camera coupled to a chromatic filter (to cancel spurious Cerenkov signal). The dwell position and time monitoring are analyzed over prostate treatment sequences with dwell times spanning from 0.1 to 11 s. The dose rate at the probe position is both evaluated from a direct measurement and by reconstruction from the measured dwell position using the AAPM TG-43 formalism.Results.A total number of 1384 dwell positions are analyzed. In average, the measured dwell positions differ by 0.023 ± 0.077 mm from planned values over a 6-54 mm source-probe distance range. The standard deviation of the measured dwell positions is below 0.8 mm. 94% of the 966 dwell positions occurring at a source-probe inter-catheter spacing below 20 mm are successfully identified, with a 100% detection rate for dwell times exceeding 0.5 s. The average deviation to the planned dwell times is of 0.005 ± 0.060 s. The instant dose retrieval from dwell position monitoring leads to a relative mismatch to planned values of 0.14% ± 0.7%.Conclusion.A miniaturized Gd2O2S:Tb detector coupled to a standard sCMOS camera can be used for time-resolved treatment monitoring in HDR Brachytherapy.

Optomagnets in nonmagnetic plasmonic nanostructures: erratum.

This erratum amends two errors in Opt. Lett.46, 613 (2021)OPLEDP0146-959210.1364/OL.411108.

Optomagnets in nonmagnetic plasmonic nanostructures.

Using a simplified hydrodynamic model of the free electron gas of a 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. Plasmonics can thus generate and tune static magnetic fields and strong magnetic forces on the nanoscale, potentially impacting small scale magnetic tweezing and sensing as well as the generation of magneto-optical effects and spin waves.

Acoustic phonon sideband dynamics during polaron formation in a single quantum dot.

When an electron-hole pair is optically excited in a semiconductor quantum dot, the host crystal lattice adapts to the presence of the generated charge distribution. Therefore, the coupled exciton-phonon system has to establish a new equilibrium, which is reached in the form of a quasiparticle called a polaron. Especially, when the exciton is abruptly generated on a timescale faster than the typical lattice dynamics, the lattice cannot follow adiabatically. Consequently, rich dynamics on the picosecond timescale of the coupled system is expected. In this study, we combine simulations and measurements of the ultrafast, coherent, nonlinear optical response, obtained by four-wave mixing (FWM) spectroscopy, to resolve the formation of this polaron. By detecting and investigating the phonon sidebands in the FWM spectra for varying pulse delays and different temperatures, we have access to the influence of phonon emission and absorption processes, which finally result in the emission of an acoustic wave packet.