Electron Paramagnetic Resonance Study of a Photosynthetic Microbial Mat and Comparison with Archean Cherts

International audienceOrganic radicals in artificially carbonized biomass dominated by oxygenic and non-oxygenic photosynthetic bacteria, Microcoleus chthonoplastes-like and Chloroflexus-like bacteria respectively, were studied by Electron Paramagnetic Resonance (EPR) spectroscopy. The two bacteria species were sampled in mats from a hypersaline lake. They underwent accelerated ageing by cumulative thermal treatments to induce progressive carbonization of the biological material, mimicking the natural maturation of carbonaceous material of Archean age. For thermal treatments at temperatures higher than 620 °C, a drastic increase in the EPR linewidth is observed in the carbonaceous matter from oxygenic photosynthetic bacteria and not anoxygenic photosynthetic bacteria. This selective EPR linewidth broadening reflects the presence of a catalytic element inducing formation of radical aggregates, without affecting the molecular structure or the microstructure of the organic matter, as shown by Raman spectroscopy and Transmission Electron Microscopy. For comparison, we carried out an EPR study of organic radicals in silicified carbonaceous rocks (cherts) from various localities, of different ages (0.42 to 3.5 Gyr) and having undergone various degrees of metamorphism, i.e. various degrees of natural carbonization. EPR linewidth dispersion for the most primitive samples was quite significant, pointing to a selective dipolar broadening similar to that observed for carbonized bacteria. This surprising result merits further evaluation in the light of its potential use as a marker of past bacterial metabolisms, in particular oxygenic photosynthesis, in Archean cherts

Beat length measurement in directional couplers by thermo-optic modulation

In integrated optical directional couplers formed by two parallel waveguides, we measure the difference Δβ = βeven - βodd between the propagation constants of the 'supermodes'. They are coupled locally by heating a fine spot on one of the guides. When the spot is scanned along the coupler the output power from one of the guides is found to vary periodically. The period of variation is the modal beat length λ = 2π/Δβ. We demonstrate this technique with directional couplers fabricated by K+-exchange in glass. Beat lengths in the range of 0.6 ... 2.2 mm are measured with an accuracy of ±0.3%.<br/

METHODOLOGY Open Access

Implementing a new EPR lineshape parameter for organic radicals in carbonaceous matte

Optical parametric oscillators : technology and applications

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High Coupling Efficiencies between Single Mode Optical Fibers and Ti Diffused LiNbO3 Waveguides

The coupling between single mode optical fibers and integrated optical devices and particularly Ti diffused LiNbO3 waveguides has been deeply investigated. Recently very good results have been obtained leading to the possibility of building pigtailed integrated optic devices (1, 2, 3).</jats:p

Limits in pyrolysis–GC–MS analysis of kerogen isolated from Archean cherts

International audiencePyrolysis-GC-MS was recently proposed as an emerging technique for establishing biogenicity of 3.5 Gyr old insoluble organic matter in cherts (Derenne et al., 2008. Earth and Planetary Science Letters 272, 476-480). When applied to four kerogens isolated from Archean chert samples for biogenicity determination, this method highlights the importance of having a significant aliphatic component remaining in the kerogen. If not, fatty acid decarboxylation may bias the n-alkane distribution. However, in most cases, mature samples such as Archean cherts usually do not have such an aliphatic fraction. This shows the limits of the technique and the need for a new biogenicity marker. (C) 2012 Elsevier Ltd. All rights reserved

Very Low Loss Waveguides and Efficient Modulators in InGaAsP/InP

Since III-V material have many applications in the field of optoelectronic components, low loss waveguides and low drive voltage modulators are considered to be key components for many future systems. Up to now, many efforts on material elaboration and technology have led to interesting waveguide characteristics (ref [1], [2], [3]) on ridge structures and on buried ones (ref [4]) with best reported propagation losses on the order of 0.4 dB/cm at 1.55 μm wavelength. Here we report on an improvement of those values (0.18 dB/cm) observed on 30.5 mm long straight waveguides and on the observation of linear and quadratic electrooptic modulation performed with those buried structures.</jats:p