Axion interpretation of the PVLAS data?

The PVLAS collaboration has recently reported the observation of a rotation of the polarization plane of light propagating through a transverse static magnetic field. Such an effect can arise from the production of a light, m_A ~ meV, pseudoscalar coupled to two photons with coupling strength g_{A\gamma} ~ 5x10^{-6} GeV^{-1}. Here, we review these experimental findings, discuss how astrophysical and helioscope bounds on this coupling can be evaded, and emphasize some experimental proposals to test the scenario.Comment: 4 pages, 1 figure, jpconf.cls, talk presented at the ninth International Conference on Topics in Astroparticle and Underground Physics, TAUP 2005, Zaragoza, Spain, September 10-14, 200

Active optical decoupling circuit for radio frequency endoluminal coil

International audienceDespite the enhanced image provided by multiple-channels array coils, an accurate exploration of bowel diseases and detailed information about the gastrointestinal wall layers are still not available. The use of endoluminal RF coil located in the region of interest could potentially allow good evaluation of tumor invasion or depth of inflammatory processes [1]. However, since metallic coaxial cables are used, patient safety is threatened due to local electric field concentration that can happen and the associated local high Specific Absorption Rate (SAR) [2]. Moreover, in this case, cable isolation and traps cannot be straightforwardly employed due to limited dimension. Signal transmission based onoptical fiber is an alternative to coaxial cables to solve definitively the electromagnetic issues. On a receiver coil, both signal transmission and decoupling have to be insured. For MR signal transmission, the electro-optical conversion has been partially validated based on electro-optic effect of some crystals [3]. In this work, an active optical decoupling circuit for endoluminal coil is presented and compared to a reference coil with regular decoupling using bias signal though coaxial cable

RF and THz Identification Using a New Generation of Chipless RFID Tags

This article presents two chipless RFID approaches where data are reading using electromagnetic waves and where the medium encoding the data is completely passive. The former approach rests on the use of RF waves (more precisely the ultra-wide band UWB). The tags developed for this application are comparable with very specific, planar, conductive, radar targets where the relation between the tag geometry and its electromagnetic signature is perfectly known and is used to encode the data. The principle of operation as well as the realization process of the RF tags presented in this paper is similar to those already reported in the literature. However, contrary to the majority of chipless RFID tags, these labels do not present an antenna function dissociated from the circuit part where the data are stored. Here, functions such as the receiver, the treatment and the emitter of the signal are closely dependent. The data storage capacity of the RF chipless tags is proportional to of the used frequency bandwidth. As radio spectrum is regulated, the number of possible encoding bits is thus strongly limited with this technology. This is the reason why we introduce a new family of tags radically different from the preceding one, where data is encoded in volume thanks to a multilayer structure operating in the THz domain. These two approaches although different are complementary and allow to increase significantly the data storage capacity of the chipless tags. Simulation and experimental results are reported in this paper for both configurations. We demonstrate a coding capacity of 3.3 bit/cm2 for RFID chipless tags and a potential 10 bits coding capacity in the THz domain

Search for weakly interacting sub-eV particles with the OSQAR laser-based experiment: results and perspectives

Recent theoretical and experimental studies highlight the possibility of new fundamental particle physics beyond the Standard Model that can be probed by sub-eV energy experiments. The OSQAR photon regeneration experiment looks for "Light Shining through a Wall" (LSW) from the quantum oscillation of optical photons into "Weakly Interacting Sub-eV Particles" (WISPs), like axion or axion-like particles (ALPs), in a 9 T transverse magnetic field over the unprecedented length of $2 \times 14.3$ m. No excess of events has been detected over the background. The di-photon couplings of possible new light scalar and pseudo-scalar particles can be constrained in the massless limit to be less than $8.0\times10^{-8}$ GeV$^{-1}$. These results are very close to the most stringent laboratory constraints obtained for the coupling of ALPs to two photons. Plans for further improving the sensitivity of the OSQAR experiment are presented.Comment: 7 pages, 7 figure

Validation du principe de conversion de champ magnétique RF par une technique électro-optique adaptée à l'IRM endoluminale

National audienceIntroduction L'exploration de zones profondes par IRM chez l'homme utilisant des capteurs externes ne permet pas toujours de réaliser des images avec une résolution spatiale suffisante. L'acquisition d'images de résolution spatiale submillimétrique peut être réalisée avec des capteurs endoluminaux placés au plus proche de la zone à explorer. Les développements de ce type de capteur ont été compromis par des aspects liés à la sécurité du patient en raison des échauffements localisés qui ont lieu avec une liaison galvanique reliant le capteur au système d'imagerie. Quelques équipes ont développé des capteurs déportés avec une transmission par fibre optique [1]. Par contre, l'utilisation de ces méthodes optiques reste limitée par des problèmes d'encombrement et la nécessité d'alimentation à l'intérieur du capteur endoluminal. Dans ce travail nous présentons une expérience permettant de mesurer un champ magnétique à l'aide d'un capteur RMN classique couplé à un cristal électro-optique (EO). Les cristaux EO présentent un indice de réfraction qui dépend linéairement de l'amplitude d'une composante du champ électrique appliquée au cristal, via l'effet Pockels. Cette propriété permet de les utiliser comme détecteurs diélectriques passifs, dédiés à la mesure vectorielle et non perturbatrice de champs électriques [2]. L'expérience est réalisée à 127 MHz, en vue de la réalisation d'une sonde endoluminale à 3T. Matériel et Méthode L'expérience, présentée sur la figure 1, a été réalisée pour valider la conversion du champ magnétique en un signal électrique. Une boucle circulaire en cuivre de 10 cm de diamètre constitue l'émetteur de champ magnétique large bande. Cette émetteur est alimenté par un synthétiseur RF fournissant un signal de fréquence 127 MHz et une puissance variant entre-60 dBm et 14 dBm. Cette puissance électrique est transformée en champs magnétique par l'émetteur. Le capteur présenté sur la figure 2a) représente un capteur RMN de base à connexion galvanique, il est adapté à 50 Ω pour une fréquence de 127 MHz. Ce capteur, placé devant la boucle émettrice RF, transforme le champ magnétique en ddp. Cette ddp est appliquée sur les deux faces opposées d'un cristal EO (LiNbO3) à l'aide de deux électrodes en cuivre. Une diode laser (=1.55 µm) émet un faisceau optique vers le cristal EO. La polarisation du faisceau est modulée en fonction de la ddp appliqué au cristal. On utilise une lame demi-onde pour placer nos mesures au maximum de linéarité et de sensibilité puis une lame quart-d'onde pour garder uniquement la modulation par effet Pockel. Cette modulation est convertie en un signal électrique à l'aide d'une photodiode. Ce signal modulé est amplifié et envoyé vers un analyseur de spectre. Résultats La figure 2b) présente la puissance mesurée () par l'analyseur de spectre en fonction de la puissance émise par le synthétiseur (). Le second axe des abscisses présente le champ magnétique B x produit par la puissance , au centre de la boucle émettrice. La courbe montre une dynamique de mesure de plus de 60 dB, une bonne linéarité et un champ magnétique minimal détectable de 163 pT. Conclusion L'amplitude du champ magnétique RMN à mesurer en IRM étant compris entre nano et micro Tesla, ces résultats montrent la faisabilité de réalisation d'une sonde dédiée à l'IRM par voie endoluminale utilisant une transmission optique

Summary of OSQAR First Achievements and Main Requests for 2008

Abstract - In the first paragraph, OSQAR foremost achievements are summarised together with a brief reminder of its scientific context. In the second paragraph, activities planned for 2008 are briefly reviewed including the expected scientific results. The third paragraph is devoted to the requests addressed to CERN as the host laboratory and as a collaboration member of the OSQAR photon regeneration experiment

Latest Results of the OSQAR Photon Regeneration Experiment for Axion-Like Particle Search

The OSQAR photon regeneration experiment searches for pseudoscalar and scalar axion-like particles by the method of "Light Shining Through a Wall", based on the assumption that these weakly interacting sub-eV particles couple to two photons to give rise to quantum oscillations with optical photons in strong magnetic field. No excess of events has been observed, which constrains the di-photon coupling strength of both pseudoscalar and scalar particles down to $5.7 \cdot 10^{-8}$ GeV$^{-1}$ in the massless limit. This result is the most stringent constraint on the di-photon coupling strength ever achieved in laboratory experiments.Comment: 6 pages, 5 figures. appears in Proceedings of the 10th PATRAS Workshop on Axions, WIMPs and WISPs (2014

Phase-locking of a 2.7-THz quantum cascade laser to a mode-locked erbium-doped fibre laser

We demonstrate phase-locking of a 2.7-THz metalmetal waveguide quantum cascade laser (QCL) to an external microwave signal. The reference is the 15th harmonic, generated by a semiconductor superlattice nonlinear device, of a signal at 182 GHz, which itself is generated by a multiplier-chain (x2x3x2) from a microwave synthesizer at 15 GHz. Both laser and reference radiations are coupled into a hot electron bolometer mixer, resulting in a beat signal, which is fed into a phase-lock loop. Spectral analysis of the beat signal (see fig. 1) confirms that the QCL is phase locked. This result opens the possibility to extend heterodyne interferometers into the far-infrared range

Predicting Crystallization of Amorphous Drugs with Terahertz Spectroscopy.

There is a controversy about the extent to which the primary and secondary dielectric relaxations influence the crystallization of amorphous organic compounds below the glass transition temperature. Recent studies also point to the importance of fast molecular dynamics on picosecond-to-nanosecond time scales with respect to the glass stability. In the present study we provide terahertz spectroscopy evidence on the crystallization of amorphous naproxen well below its glass transition temperature and confirm the direct role of Johari-Goldstein (JG) secondary relaxation as a facilitator of the crystallization. We determine the onset temperature Tβ above which the JG relaxation contributes to the fast molecular dynamics and analytically quantify the level of this contribution. We then show there is a strong correlation between the increase in the fast molecular dynamics and onset of crystallization in several chosen amorphous drugs. We believe that this technique has immediate applications to quantify the stability of amorphous drug materials.JS and JAZ would like to acknowledge the UK Engineering and Physical Sciences Research Council for funding (EP/J007803/1).This is the final version of the article. It first appeared from ACS at http://dx.doi.org/10.1021/acs.molpharmaceut.5b0033