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Hasnaoui A.,University of Science and Technology Houari Boumediene | Ait-Ameur K.,CNRS Center for Research on Ions, Materials and Photonics
Applied Optics | Year: 2010

This paper considers the transverse optical properties of an absorbing ring when it is lighted by a symmetrical Laguerre-Gauss beam TEMp0. It is demonstrated that the insertion of an opaque ring having adequate size inside a diaphragmed laser cavity is able to improve greatly (rate of about 100%) the discrimination between the TEM00 and the TEM10 modes, while keeping the diffraction losses unchanged or even decreased. © 2010 Optical Society of America.

Molard Y.,CNRS Chemistry Institute of Rennes | Labbe C.,CNRS Center for Research on Ions, Materials and Photonics | Cardin J.,CNRS Center for Research on Ions, Materials and Photonics | Cordier S.,CNRS Chemistry Institute of Rennes
Advanced Functional Materials | Year: 2013

Luminescent hybrid copolymers are obtained by copolymerizing in bulk methylmethacrylate with a methacrylic acid (MAC) solution containing [n-Bu 4N]2[Mo6Br8(MAC)6], and aliquots of an Er(TMHD)3 complex (TMHD for 2,2,6,6-tetramethyl-3,5- heptanedione) solution. This leads to novel homogeneous and transparent hybrid materials in which the Er3+ infrared luminescence at 1.55 μm, a standard wavelength for telecommunication applications, is up to six time more intense in the presence of Mo6 clusters when samples are irradiated at 476.5 nm. This work demonstrates the outstanding potential of Mo6 clusters, compounds obtained by high-temperature solid-state synthesis, in the design of functional hybrid materials via soft chemistry routes. Integrating Er3+ ions in a hybrid Mo6-PMMA hybrid matrix enables the sensitization of its IR photoluminescence upon irradiation anywhere in the octahedral metallic cluster absorption band. Meanwhile, it causes a noticeable decrease of the Mo6 red luminescence. Mo6 clusters being covalently linked to polymer strands, the hybrid material shows excellent aging behavior, leaving promising perspectives for telecom applications. Copyright © 2013 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Wang Y.,CNRS Center for Research on Ions, Materials and Photonics | Ruterana P.,CNRS Center for Research on Ions, Materials and Photonics
Applied Physics Letters | Year: 2013

The misfit dislocations at cubic semiconductors hetero-interfaces were quantitatively investigated by high angle dark field scanning transmission electron microscopy in combination with geometric phase analysis and dislocation density tensor analysis. A detailed comparison of the extracted information with the available dislocation models (Peierls-Nabarro and Foreman model) in bulk materials shows that these models can be adapted to the misfit dislocations at lattice mismatched interface. A typical illustration is made for GaSb/GaAs, where it is shown that the strain fields of the 60° dislocation follows the Foreman model (a = 1.8), in case of the Lomer and 60° dislocation pair, the Foreman (a = 2.5) and Peierls-Nabarro model apply for εxx and εyy, respectively. © 2013 AIP Publishing LLC.

Moncorge R.,CNRS Center for Research on Ions, Materials and Photonics
Optical Materials | Year: 2016

The purpose of this presentation is to review the spectroscopic properties of the main laser materials based on transition metal ions which lead to noticeable laser performance at room temperature and, for very few cases, because of unique properties, when they are operated at cryogenic temperatures. The description also includes the materials which are currently being used as saturable absorbers for passive-Q-switching of a variety of other near- and mid-infrared solid state lasers. A substantial part of the article is devoted first to the description of the energy levels and of the absorption and emission transitions of the transition metal ions in various types of environments by using the well-known Tanabe-Sugano diagrams. It is shown in particular how these diagrams can be used along with other theoretical considerations to understand and describe the spectroscopic properties of ions sitting in crystal field environments of near-octahedral or near-tetrahedral symmetry. The second part is then dedicated to the description (positions and intensities) of the main absorption and emission features which characterize the different types of materials. © 2016.

Marion L.F.,CEA Saclay Nuclear Research Center | Monnet I.,CNRS Center for Research on Ions, Materials and Photonics
Journal of Nuclear Materials | Year: 2013

The good radiation resistance of Ti3(Si1-xAl x)C2 (x = 0.05, 0.07, 0.1) has been recently demonstrated through 95 MeV Xe irradiations up to 2 × 1019 m-2 which did not induce amorphisation. In this work, the irradiation damage level of Ti3(Si0.95Al0.05)C2 was raised up to 4.5 × 1019 m-2: saturation of hardness above 1019 cm-2 suggests saturation of microstructure disorder. Same conclusions could be deduced from irradiation of (Ti0.95Zr 0.05)(Si0.9Al0.1)C2. © 2012 Elsevier B.V. All rights reserved.

Ngono-Ravache Y.,CNRS Center for Research on Ions, Materials and Photonics
Journal of Physics: Conference Series | Year: 2015

This paper gathers results obtained on the chemical ageing of polymers, at the CIRIL platform, using Swift heavy ions (SHI) from the GANIL accelerator. Swift heavy ions induce high values of electronic stopping power or LET (Linear Energy Transfer) and deposit their energy in the polymer through electronic processes, in a few nanometer size cylinder centered on the ion path. This results in huge local doses and dose rates. Both defects created in the polymer chain and gas release were quantified using spectroscopic methods (FTIR and Residual gas analysis (RGA)). Defects created in polymers submitted to SHI can be separated in two main series: defects common to all ionizing radiations and defects specific to SHI. A common trend of the evolution of these defects, under inert environment, is the following: 1) for the first group of defects, in most of the polyolefins, there is a limited (if inexistent) effect of LET on the radiation chemical yield of creation at low doses. Among defects of this first series, the behavior of vinyl groups is particular, 2) LET effect on SHI specific defects (triple bonds and cumulenes) is tremendous. Triple bonds (alkynes, alkyl or aryl cyanates) are created after a LET threshold value, depending on the polymer chemical structure. The dose effect on macromolecular defects, under inert environment, is also presented. The study of the LET effect on gas release, in various polyolefines, gives an insight on the mechanism of bond cleavage in presence of high ionization and excitation densities. Finally, few results on radiation-induced oxidation are presented. Compared to low-ionizing radiations, oxidation is reduced and unsaturated bonds are created under SHI. © Published under licence by IOP Publishing Ltd.

Ait-Ameur K.,CNRS Center for Research on Ions, Materials and Photonics
Optics Communications | Year: 2012

We consider the transverse characteristics of a Gaussian laser beam subject to a phase or amplitude clipping due to a pupil which is a π-plate or an opaque disc (stop). In particular, we consider the correlation between two features, the Strehl ratio and divergence angle, usually used for characterising the focusability of a diffracted beam. It is demonstrated that the Strehl ratio does not give systematically a global view, from a divergence point of view, on the transverse properties of a Gaussian beam suffering amplitude or phase diffraction. In addition, we consider the case of self-diffraction of a Gaussian beam upon a Gaussian phase aberration of same width, and it is found that the on-axis intensity describes correctly the whole diffracted beam cross-section, from a divergence point of view, only if the central phase shift is smaller than π. Another example showing that the focusability of a pure high-order Laguerre-Gauss TEM p0 beam, free from any clipping, cannot be correctly described by Strehl ratio is also considered. © 2011 Elsevier B.V. All rights reserved.

Benyagoub A.,CNRS Center for Research on Ions, Materials and Photonics
Acta Materialia | Year: 2012

Zirconia and hafnia are known to exhibit similar phase transitions under temperature, pressure or swift heavy (i.e., GeV) ion irradiation. In the present study, both monoclinic zirconia and hafnia were irradiated with 5-MeV I ions in order to comprehend the underlying mechanism governing phase transition by low-energy ion irradiation. Surprisingly, it was found that, although monoclinic zirconia can easily transform to the tetragonal phase, monoclinic hafnia does not show any transition to the tetragonal structure even after irradiation with ∼19 displacements per atom. The absence of this phase transition in hafnia and its presence in zirconia clearly break the parallel between these two oxides in their response to intense excitation. Furthermore, this comparative study allowed severe constraints to be imposed on the possible mechanisms aimed at explaining phase transformation by low-energy ion irradiation. It is found that the monoclinic-to-tetragonal phase transition in these oxides is very likely driven by oxygen vacancies and occurs once their concentration reaches a certain value. The absence of phase transition in hafnia can thus be explained by the lower concentration level attained by these defects, owing to their higher diffusivity in this material. A similar mechanism can also be invoked to explain the remarkable phase stability of tetragonal zirconia under prolonged low-energy ion irradiation. © 2012 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.

Fremont F.,CNRS Center for Research on Ions, Materials and Photonics
Journal of Physics B: Atomic, Molecular and Optical Physics | Year: 2016

A classical model is used to study electron capture and single ionization (SI) following H+ + Ar collisions at projectile energies varying from 400 to 40 keV. In the present model, the Ar electrons are treated independently from each other, and only the 3s and 3p electrons are supposed to be captured by the projectile. In addition, a Coulombic potential with an effective charge Z eff = 6.75, derived from Slater rules, is used in the calculations to simulate the screening of the Ar nucleus due to the presence of the core and 2l electrons. Total cross sections for single electron capture and SI are calculated and compared with previous experiments and earlier calculations based on a semiclassical approach. The reasonable agreement we observed allows a preliminary study of double electron capture (DC). The total cross section for DC is found to be much larger than the experimental one. Possible reasons for this disagreement are discussed. © 2016 IOP Publishing Ltd.

Benyagoub A.,CNRS Center for Research on Ions, Materials and Photonics
Nuclear Instruments and Methods in Physics Research, Section B: Beam Interactions with Materials and Atoms | Year: 2010

It is now well established that the irradiation of pure zirconia (ZrO 2) with swift heavy ions can lead to a transformation from the monoclinic to the tetragonal phase when the deposited electronic energy loss exceeds an effective threshold ∼12 keV nm-1. Previous swift heavy ion irradiations carried out with electronic energy losses less than ∼30 keV nm-1 evidenced that this phase transition is characterized by two constant features: (i) it is driven by a double ion impact process, and (ii) it is never complete even at extremely high fluences. It is then quite interesting to check whether this phase transformation does not depart from this behaviour at very high electronic energy losses. For this purpose, zirconia was irradiated with 0.6-GeV Pb ions giving rise to an electronic energy loss ∼42 keV nm-1 at the sample surface. Despite this huge value, the experimental data revealed that the phase change is here again still characterized by a double ion impact process. However, contrary to previous cases, it was found that this phase transformation not only occurs very rapidly but achieves full completion at rather low fluences. © 2010 Elsevier B.V. All rights reserved.

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