Photonic and Optomechanical Thermometry

Temperature is one of the most relevant physical quantities that affects almost all processes in nature. However, the realization of accurate temperature standards using current temperature references, like the triple point of water, is difficult due to the requirements on material purity and stability of the environment. In addition, in harsh environments, current temperature sensors with electrical readout, like platinum resistors, are difficult to implement, urging the development of optical temperature sensors. In 2018, the European consortium Photoquant, consisting of metrological institutes and academic partners, started investigating new temperature standards for self-calibrated, embedded optomechanical sensor applications, as well as optimised high resolution and high re- liability photonic sensors, to measure temperature at the nano and meso-scales and as a possible replacement for the standard platinum resistant thermometers. This article presents an overview of the results obtained with sensor prototypes that exploit photonic and optomechanical techniques for sensing temperatures over a large temperature range (5 K to 300 K). Different concepts are demon- strated, including ring resonators, ladder-like resonators and suspended membrane optomechanical thermometers, highlighting initial performance and challenges, like self-heating that need to be overcome to realize photonic and optomechanical thermometry applications.This work was carried out under the 17FUN05 PhotOQuanT project, which has received funding from the EMPIR program, co-financed by the Participating States and the European Union’s Horizon 2020 research and innovation progra

Magnetoplasmonics of ferromagnetic nanostructures

Plasmonics plays a key role in the development of advanced nanophotonics. Via the excitation of surface plasmons light can couple to subwavelength nanostructures. Active control of localized light opens up new avenues toward controllable nanophotonic devices. Magneto-optically active materials can introduce tunability and multifunctionality into passive plasmonic devices. In this thesis, the interaction between light and ferromagnetic nanostructures is investigated.In ferromagnetic nanoparticles that support the excitation of surface plasmons, spin-orbit coupling induces two electrical dipoles, one along the direction of the incident electric field and the second orthogonally to the first and the magnetization direction. The amplitude and phase relations of these two dipoles determine the magneto-optical response of the system upon transmission or reflection.Periodic arrangements of metal nanostructures lead to coupling between diffracted waves in the surface plane and localized surface plasmon resonances. The resulting surface lattice resonances enhance the magneto-optical signal of ferromagnetic systems. Further tailoring of the magneto-optical activity can be attained by combining ferromagnetic and noble metals. Two effects are studied here: Farfielddiffracted coupling between ferromagnetic and noble metal nanodisks in checkerboard arrays and vertical dimer structures that comprise ferromagnetic and noble metals within a single nanoparticle. If dimers are arranged into a periodic lattice, the magneto-optical response is resonantly enhanced by near- and farfield coupling between the two metals, a feature that is demonstrated to be attractive for high-resolution refractive index sensing. As a mechanism to overcome optical losses in magnetoplasmonic nanostructures, lasing in ferromagnetic nanoparticle arrays overlaid with an organic gain medium is demonstrated. The experimental results on magnetoplasmonic effects in ferromagnetic nanostructures arereproduced by models based on the modified long wavelength approximation (MLWA) and discrete dipole approximation (DDA)

Ultra-Stable, Continuous-Wave UV Light Source for Precision Thermometry

An ultra-stable light source and optical detection set-up for high-precision measurements of 114Cd absorption lines is presented. The experimental setup for ultraviolet light at 326.2 nm is described with an aim toward primary thermometry.</p

Magnetic circular dichroism of non-local surface lattice resonances in magnetic nanoparticle arrays

Subwavelength metallic particles support plasmon resonances that allow extreme confinement of light down to the nanoscale. Irradiation with left- and right hand circularly polarized light results in the excitation of circular plasmon modes with opposite helicity. The Lorenz force lifts the degeneracy of the two modes in magnetic nanoparticles. Consequently, the confinement and frequency of localized surface plasmon resonances can be tuned by an external magnetic field. In this paper, we experimentally demonstrate this effect for nickel nanoparticles using magnetic circular dichroism (MCD). Besides, we show that non-local surface lattice resonances in periodic arrays of the same nanoparticles significantly enhance the MCD signal. A numerical model based on the modified long wavelength approximation is used to reproduce the main features in the experimental spectra and provide design rules for large MCD effects in sensing applications.Peer reviewe

Tunable magnetoplasmonics in lattices of Ni/SiO2/Au dimers

| openaire: EC/H2020/737093/EU//FEMTOTERABYTEWe present a systematic study on the optical and magneto-optical properties of Ni/SiO2/Au dimer lattices. By considering the excitation of orthogonal dipoles in the Ni and Au nanodisks, we analytically demonstrate that the magnetoplasmonic response of dimer lattices is governed by a complex interplay of near- and far-field interactions. Near-field coupling between dipoles in Ni and low-loss Au enhances the polarizabilty of single dimers compared to that of isolated Ni nanodisks. Far-field diffractive coupling in periodic lattices of these two particle types enlarges the difference in effective polarizability further. This effect is explained by an inverse relationship between the damping of collective surface lattice resonances and the imaginary polarizability of individual scatterers. Optical reflectance measurements, magneto-optical Kerr effect spectra, and finite-difference time-domain simulations confirm the analytical results. Hybrid dimer arrays supporting intense plasmon excitations are a promising candidate for active magnetoplasmonic devices.Peer reviewe

Hybrid Ni/SiO2/Au dimer arrays for high-resolution refractive index sensing

We introduce a novel magnetoplasmonic sensor concept for sensitive detection of refractive index changes. The sensor consists of a periodic array of Ni/SiO2/Au dimer nanodisks. Combined effects of near-field interactions between the Ni and Au disks within the individual dimers and far-field diffractive coupling between the dimers of the array produce narrow linewidth features in the magneto-optical Faraday spectrum. We associate these features with the excitation of surface lattice resonances and show that they exhibit a spectral shift when the refractive index of the surrounding environment is varied. Because the resonances are sharp, refractive index changes are accurately detected by tracking the wavelength where the Faraday signal crosses 0. Compared to random distributions of pure Ni nanodisks or Ni/SiO2/Au dimers or periodic arrays of Ni nanodisks, the sensing figure of merit of the hybrid magnetoplasmonic array is more than one order of magnitude larger.Peer reviewe

Hybrid plasmonic lattices with tunable magneto-optical activity

| openaire: EC/FP7/340748/EU//CODEWe report on the optical and magneto-optical response of hybrid plasmonic lattices that consist of pure nickel and gold nanoparticles in a checkerboard arrangement. Diffractive far-field coupling between the individual emitters of the lattices results in the excitation of two orthogonal surface lattice resonance modes. Local analyses of the radiation fields indicate that both the nickel and gold nanoparticles contribute to these collective resonances and, thereby, to the magneto-optical activity of the hybrid arrays. The strong effect of noble metal nanoparticles on the magneto-optical response of hybrid lattices opens up new avenues for the realization of sensitive and tunable magneto-plasmonic nanostructures.Peer reviewe

Lasing in Ni Nanodisk Arrays

We report on lasing at visible wavelengths in arrays of ferromagnetic Ni nanodisks overlaid with an organic gain medium. We demonstrate that by placing an organic gain material within the mode volume of the plasmonic nanoparticles both the radiative and, in particular, the high ohmic losses of Ni nanodisk resonances can be compensated. Under increasing pump fluence, the systems exhibit a transition from lattice-modified spontaneous emission to lasing, the latter being characterized by highly directional and sub-nanometer line width emission. By breaking the symmetry of the array, we observe tunable multimode lasing at two wavelengths corresponding to the particle periodicity along the two principal directions of the lattice. Our results are relevant for loss-compensated magnetoplasmonic devices and topological photonics.publishedVersionPeer reviewe

Photonic and Optomechanical Thermometry

International audienceTemperature is one of the most relevant physical quantities that affects almost all processes in nature. However, the realization of accurate temperature standards using current temperature references, like the triple point of water, is difficult due to the requirements on material purity and stability of the environment. In addition, in harsh environments, current temperature sensors with electrical readout, like platinum resistors, are difficult to implement, urging the development of optical temperature sensors. In 2018, the European consortium Photoquant, consisting of metrological institutes and academic partners, started investigating new temperature standards for self-calibrated, embedded optomechanical sensor applications, as well as optimised high resolution and high reliability photonic sensors, to measure temperature at the nano and meso-scales and as a possible replacement for the standard platinum resistant thermometers. This article presents an overview of the results obtained with sensor prototypes that exploit photonic and optomechanical techniques for sensing temperatures over a large temperature range (5 K to 300 K). Different concepts are demonstrated, including ring resonators, ladder-like resonators and suspended membrane optomechanical thermometers, highlighting initial performance and challenges, like self-heating that need to be overcome to realize photonic and optomechanical thermometry applications