Le champ proche optique. Théorie et applications

International audienceCe livre est le résultat d'une collaboration d'une dizaine d'années entre plusieurs des auteurs, née dans le cadre du programme ULTIMATECH du CNRS. À travers ce programme, de nombreux liens s'étaient tissés entre les membres de la communauté des opticiens du champ proche en France, renforcés par la création d'un Groupement de Recherche CNRS et concrétisés par l'organisation d'une École Thématique qui s'est tenue en mars 2000 à La Londe les Maures (Var). Cette école qui a accueilli une centaine de participants nous a permis de faire le point sur l'état de l'art dans ce nouveau domaine grâce à une série de cours portant autant sur la théorie que sur l'expérience. La qualité des interventions nous ont convaincus qu'une compilation fournirait un outil pour le chercheur et l'ingénieur qu'il soit jeune ou confirmé

LiTaO3/Silicon Composite Wafers for the Fabrication of Low Loss Low TCF High Coupling Resonators for Filter Applications

AbstractSAW devices are widely used for radio-frequency (RF) telecommunication filtering and the number of SAW filters, resonators or duplexers is still increasing in RF stage of cellular phones. Therefore, a strong effort is still dedicated to reduce as much as possible their sensitivity to environmental parameter and more specifically to temperature. Bounding processes have been developed at FEMTO-ST and CEA-LETI using either Au/Au or direct bonding techniques for the fabrication of composite wafers combining materials with very different thermoelastic properties, yielding innovative solutions for about-zero temperature coefficient of frequency (TCF) bulk acoustic wave devices. In the present work, this approach has been applied to (YXl)/42∘ lithium tantalate plates, bounded onto (100) silicon wafers and thinned down to 25μm. The leading idea already explored by other groups as mentioned in introduction consists in impeding the thermal expansion of the piezoelectric material using silicon limited expansion. 2GHz resonators have been built on such plates and tested electrically and thermally, first by tip probing. A dramatic reduction of the TCF is observed for all the tested devices, allowing to reduce the thermal drift of the resonators down to a few ppm.K-1 within the standard temperature range. We then propose an analysis of the frequency-temperature behavior of the device to improve the resonator design to use these wafers for industrial applications

Correction to the Casimir force due to the anomalous skin effect

The surface impedance approach is discussed in connection with the precise calculation of the Casimir force between metallic plates. It allows to take into account the nonlocal connection between the current density and electric field inside of metals. In general, a material has to be described by two impedances $Z_{s}(\omega,q)$ and $Z_{p}(\omega,q)$ corresponding to two different polarization states. In contrast with the approximate Leontovich impedance they depend not only on frequency $\omega$ but also on the wave vector along the plate $q$. In this paper only the nonlocal effects happening at frequencies $\omega<\omega_{p}$ (plasma frequency) are analyzed. We refer to all of them as the anomalous skin effect. The impedances are calculated for the propagating and evanescent fields in the Boltzmann approximation. It is found that $Z_p$ significantly deviates from the local impedance as a result of the Thomas-Fermi screening. The nonlocal correction to the Casimir force is calculated at zero temperature. This correction is small but observable at small separations between bodies. The same theory can be used to find more significant nonlocal contribution at $\omega\sim\omega_p$ due to the plasmon excitation.Comment: 29 pages. To appear in Phys. Rev.

Theory of imaging a photonic crystal with transmission near-field optical microscopy

While near-field scanning optical microscopy (NSOM) can provide optical images with resolution much better than the diffraction limit, analysis and interpretation of these images is often difficult. We present a theory of imaging with transmission NSOM that includes the effects of tip field, tip/sample coupling, light propagation through the sample and light collection. We apply this theory to analyze experimental NSOM images of a nanochannel glass (NCG) array obtained in transmission mode. The NCG is a triangular array of dielectric rods in a dielectric glass matrix with a two-dimensional photonic band structure. We determine the modes for the NCG photonic crystal and simulate the observed data. The calculations show large contrast at low numerical aperture (NA) of the collection optics and detailed structure at high NA consistent with the observed images. We present calculations as a function of NA to identify how the NCG photonic modes contribute to and determine the spatial structure in these images. Calculations are presented as a function of tip/sample position, sample index contrast and geometry, and aperture size to identify the factors that determine image formation with transmission NSOM in this experiment.Comment: 28 pages of ReVTex, 14 ps figures, submitted to Phys. Rev.

Computing the optical near-field distributions around complex subwavelength surface structures: A comparative study of different methods

Some 15 years ago, optical topographic signals with subwavelength resolution were obtained independently by several experimental teams. Since this exploratory period, a growing number of experimental configurations have been proposed and continuously developed. Simultaneously, this research field was supported by different theoretical works, aimed at developing our understanding of the interaction of optical fields with mesoscopic objects. Over the past three years, several theoretical frameworks have been proposed (Green's functions, field susceptibility, boundary conditions methods, multiple multipoles expansions, etc.). In this paper, an attempt at a careful comparison between two classes of numerical models is presented. Using the same test object, we discuss and compare the numerical solutions issued from a reciprocal-space perturbative method (Rayleigh approximation) and the solution originating from a direct-space integral approach (Green's function or field susceptibility). The discussion is given for different values of the relevant experimental parameters. The convergence of both approaches is investigated

Pseudo-surface acoustic waves in hypersonic surface phononic crystals

We present a theoretical framework allowing to properly address the nature of surfacelike eigenmodes in a hypersonic surface phononic crystal, a composite structure made of periodic metal stripes of nanometer size and periodicity of 1 um, deposited over a semi-infinite silicon substrate. In surface-based phononic crystals there is no distinction between the eigenmodes of the periodically nanostructured overlayer and the surface acoustic modes of the semi-infinite substrate, the solution of the elastic equation being a pseudosurface acoustic wave partially localized on the nanostructures and radiating energy into the bulk. This problem is particularly severe in the hypersonic frequency range, where semi-infinite substrate s surface acoustic modes strongly couple to the periodic overlayer, thus preventing any perturbative approach. We solve the problem introducing a surface-likeness coefficient as a tool allowing to find pseudosurface acoustic waves and to calculate their line shapes. Having accessed the pseudosurface modes of the composite structure, the same theoretical frame allows reporting on the gap opening in the now well-defined pseudo-SAW frequency spectrum. We show how the filling fraction, mass loading, and geometric factors affect both the frequency gap, and how the mechanical energy is scattered out of the surface waveguiding modes

Breakthrough infections due to SARS-CoV-2 Delta variant: relation to humoral and cellular vaccine responses

IntroductionCOVID-19 vaccines are expected to provide effective protection. However, emerging strains can cause breakthrough infection in vaccinated individuals. The immune response of vaccinated individuals who have experienced breakthrough infection is still poorly understood.MethodsHere, we studied the humoral and cellular immune responses of fully vaccinated individuals who subsequently experienced breakthrough infection due to the Delta variant of SARS-CoV-2 and correlated them with the severity of the disease.ResultsIn this study, an effective humoral response alone was not sufficient to induce effective immune protection against severe breakthrough infection, which also required effective cell-mediated immunity to SARS-CoV-2. Patients who did not require oxygen had significantly higher specific (p=0.021) and nonspecific (p=0.004) cellular responses to SARS-CoV-2 at the onset of infection than those who progressed to a severe form.DiscussionKnowing both humoral and cellular immune response could allow to adapt preventive strategy, by better selecting patients who would benefit from additional vaccine boosters.Trial registration numbershttps://clinicaltrials.gov, identifier NCT04355351; https://clinicaltrials.gov, identifier NCT04429594

Surface Plasmon mediated near-field imaging and optical addressing in nanoscience

We present an overview of recent progress in plasmonics. We focus our study on the observation and excitation of surface plasmon polaritons (SPPs) with optical near-field microscopy. We discuss in particular recent applications of photon scanning tunnelling microscope (PSTM) for imaging of SPP propagating in metal and dielectric wave guides. We show how near-field scanning optical microscopy (NSOM) can be used to optically and actively address remotely nano-objects such as quantum dots. Additionally we compare results obtained with near-field microscopy to those obtained with other optical far-field methods of analysis such as leakage radiation microscopy (LRM)

French national cohort of first use of dalbavancin: a high proportion of off-label use

Dalbavancin is a glycopeptide antibiotic with a long half-life, recently marketed in Europe for skin and soft tissue infections (SSTI), but real-life use is not well-known. We aimed to describe all first prescriptions in France over an 18-month period. We performed a retrospective study on all adult patients who received at least one dose of dalbavancin from July 1, 2017 to September 31, 2018. Data were collected thanks to a standard questionnaire. Failure was defined as: persistent or reappearance of signs of infection; and/or switch to suppressive antibiotic treatment; and/or death from infection. We included 75 patients from 29 French hospitals. Main indications were bone and joint infections (BJIs) (64.0%), endocarditis (25.3%), and SSTIs (17.3%). Main bacteria involved were: Staphylococcus aureus (51.4%), including methicillin-resistant S. aureus (MRSA) (19.4%); and coagulase-negative staphylococci (CNS) (44.4%). Median MICs for staphylococci to vancomycin and dalbavancin ranged from 0.875 mg/L to 2.0 mg/L, and 0.040 mg/L to 0.064 mg/L, respectively. Dalbavancin was used after a mean of 2.3 ± 1.2 lines of antimicrobial treatment. Main treatment regimens for dalbavancin were a weekly 2-dose regimen (1500mg each) in 38 (53.2%) cases, and a single-dose regimen (1500mg) in 13 (18.3%) cases. Overall, at the patients\u27 last visit, clinical cure was observed in 54/72 patients, while failure was found in 14/72 patients. First uses of dalbavancin in France were mostly off-label. Most of them were due to BJIs, and often as rescue therapy for severe infections. Even in off-label situations, dalbavancin seems safe and effective