Tailoring the morphology of photowritten buried waveguides by helical trajectory in As2S3 glass

International audienceThis paper deals with the control of the refractive index variation (Δn) profile induced by femtosecond laser irradiation in the bulk of As2S3 glass. The writing technique consists of an original laser inscription based on a helical translation of the sample parallel to the laser beam. Instead of inscribing the core of the waveguide as usually performed, the laser beam is used to induce a negative refractive index variation and consequently to write the cladding of the waveguide. However, it should be noticed that the matter displacement resulting from local heating leads to a densification at the center of the helix which induces a positive Δn relatively to the matrix. Therefore, the structure of Δn is complex, being composed of a positive core surrounded by a negative cladding. The influence of different parameters on the Δn profiles such as the sample translation velocity, the pitch and the radius of the helical displacement, and the pulse energy are analysed. This study demonstrates that both Δn and its diameter can be varied in a wide range of values and picked independently, allowing the design of single or multimode buried infrared waveguid

Influence of NaX (X=I or Cl) additions on GeS2-​Ga2S3 based glasses

International audienceChalcogenide glasses in the pseudo-​ternary system NaX-​GeS2-​Ga2S3 (X=Cl or I) were synthesized. Different series were investigated in order to highlight the influence of the sodium halide addn. on two different host glasses (GeS2)​80(Ga2S3)​20 and (GeS2)​72(Ga2S3)​28. Macroscopic properties including d. and characteristic temps., such as glass transition temps. Tg and crystn. temp. Tx, were detd. for a max. molar content of NaX equal to 15​%. The evolution of the optical band-​gap and the chem. stability following the compn. were also studied. Cond. measurements were also performed and compared to other Li-​based GeS2-​Ga2S3 glasses. The results were discussed taking into account the cation and anion nature and also the glass packing d

Electrical, dielectric, and optical properties of Sb2O3–Li2O–MoO3 glasses

International audienceTemperature and frequency dependencies of DC and AC conductivities, dielectric response, static permittivity, optical absorption edge, infrared absorption spectrum, density, and temperatures of glass transition and crystallization for lithium molybdenum–antimonite glasses, (80 − x)Sb2O3–20Li2O–xMoO3, where x = 0–40, are measured and discussed. The DC conductivity increases with increasing concentration of MoO3. At 150 °C, it ranges from 5 × 10− 11 S/m up to 3 × 10− 8 S/m. Polaron hopping between Mo5 + and Mo6 + ions contributes, probably, to the DC conductivity. Ionic conductivity by Li+ ions is also present. The conduction activation energy monotonously decreases from 1.15 eV, at x = 5, down to 0.91 eV, at x = 40. In all glasses with x > 0, the conduction activation energy is close to a half of the indirect allowed optical gap. The pre-exponential factor, σ0, goes through a sharp maximum close to the composition (x = 20) with both the highest glass transition temperature and the largest thermal stability range. The frequency dependence of the AC conductivity is composed of three components — the DC conductivity and two AC components. For x = 35 and 40, the activation energy of electrical relaxation is equal to 0.954 ± 0.008 eV and the pre-exponential factor of relaxation times is equal to (4 ± 1) 10− 14 s. The static relative permittivity ranges from 17.4 to 23.0. Strong extrinsic absorption bands in infrared region originate from hydroxyl ions, CO2 impurities, and silicon–oxygen vibrations. The UV–visible indirect allowed absorption edge shifts from 2.6 eV to 2.1 eV with increasing MoO3 content. With increasing MoO3 content the glasses darken, from a light yellow color, at x = 0, to a deep brown color, at x = 40

Mobile DNA elements in T4 and related phages

Mobile genetic elements are common inhabitants of virtually every genome where they can exert profound influences on genome structure and function in addition to promoting their own spread within and between genomes. Phage T4 and related phage have long served as a model system for understanding the molecular mechanisms by which a certain class of mobile DNA, homing endonucleases, promote their spread. Homing endonucleases are site-specific DNA endonucleases that initiate mobility by introducing double-strand breaks at defined positions in genomes lacking the endonuclease gene, stimulating repair and recombination pathways that mobilize the endonuclease coding region. In phage T4, homing endonucleases were first discovered as encoded within the self-splicing td, nrdB and nrdD introns of T4. Genomic data has revealed that homing endonucleases are extremely widespread in T-even-like phage, as evidenced by the astounding fact that ~11% of the T4 genome encodes homing endonuclease genes, with most of them located outside of self-splicing introns. Detailed studies of the mobile td intron and its encoded endonuclease, I-TevI, have laid the foundation for genetic, biochemical and structural aspects that regulate the mobility process, and more recently have provided insights into regulation of homing endonuclease function. Here, we summarize the current state of knowledge regarding T4-encoded homing endonucleases, with particular emphasis on the td/I-TevI model system. We also discuss recent progress in the biology of free-standing endonucleases, and present areas of future research for this fascinating class of mobile genetic elements

Pure transfer

International audienc

Pure transfer

International audienc

Femtosecond Laser Fabrication of Gradient Refractive Index Micro-Lenses in Chalcogenide Glass for Applications in Visible and Infrared Region

International audienceGradient refractive index (GRIN) lenses are optical components having spatial variations of in the material [1]. GRIN have been widely used for several applications such as correction aberrations [2], fiber coupling [3], imaging systems [4]. Many techniques developed fabrication lenses: chemical vapor deposition, ion exchange or neutron irradiation [5]. However, these cannot be applied all materials because their use depends composition [6]. In addition, femtosecond laser direct writing (FLDW) method is a very flexible technique to modify materials. This powerful allows controlling inscribed shape [6], especially scale <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">$\mu \mathrm{m}$</tex> . this work, we focus on micro-lenses chalcogenide glasses (ChG) using FLDW method

Nouvelle méthode d'élaboration de fibres optiques double indice en verre de chalcogénures. Application à la spectroscopie infrarouge

Des fibres optiques double indice en verre TAS (Te/As/Se) ont été élaborées à partir d'une préforme réalisée par un nouveau procédé en tube scellé sous vide. Il permet d'obtenir des interfaces coeur/gaine de parfaite qualité et des rapports de diamètre pouvant varier de 0,25 à 0,75. Leurs pertes optiques sont actuellement de 1,7 dB/m entre 6,5 et 9,5 æm. Des solutions de polissage chimique, préparées à partir d'acide sulfurique concentré et d'un oxydant ont été étudiées. Le traitement chimique, réalisé sur des échantillons, permet d'améliorer leur état de surface, tout en conservant les propriétés de transmission infrarouge. Les vitesses de dissolution peuvent atteindre des vitesses de l'ordre de 50 æm/h.Les fibres monoindice en verre TAS sont utilisées en spectroscopie par onde évanescente dans la région 2 - 12 æm. Le polissage chimique permet d'effiler les fibres monoindice et l'accès au coeur des fibres double indice, pour les utiliser en tant que capteur chimique.RENNES1-BU Sciences Philo (352382102) / SudocSudocFranceF