Les nouvelles générations de détecteurs infrarouge à base de HgCdTeNew generations of infrared detectors based on HgCdTe

The technology of very high performance cooled infrared detectors made with HgCdTe has progressed continuously for ten years and reached today an industrial maturity that allows the production of large size arrays at a more and more reasonable cost. At the same time, new prototypes of more complex sensors have appeared (megapixel arrays, multicolour arrays, high definition long linear arrays, …) that show the strong potentialities of this very high performance technology. This paper presents the technology developed in France and gives the state of the art of products available in industry; it then focuses on some very recent realizations of advanced prototypes made at LETI (dualband arrays, megapixel arrays, …). To cite this article: G. Destefanis, C. R. Physique 4 (2003).     

La détection infrarouge avec les plans focaux non refroidis : état de l'artUncooled focal plane infrared detectors: the state of the art

The emergence of uncooled detectors has opened new opportunities for IR detection for both military and commercial applications. Development of such devices involves a lot of trade-offs between the different parameters that define the technological stack. These trade-offs explain the number of different architectures that are under worldwide development. The key factor is to find a high sensitivity and low noise thermometer material compatible with silicon technology in order to achieve high thermal isolation in the smallest area as possible. Ferroelectric thermometer based hybrid technology and electrical resistive thermometer based (microbolometer) technology are under development. LETI and ULIS have chosen from the very beginning to develop first a monolithic microbolometer technology fully compatible with commercially available CMOS technology and secondly amorphous silicon based thermometer. This silicon approach has the greatest potential for reducing infrared detector manufacturing cost. After the development of the technology, the transfer to industrial facilities has been performed in a short period of time and the production is now ramping up with ULIS team in new facilities. LETI and ULIS are now working to facilitate the IRFPA integration into equipment in order to address a very large market. Achievement of this goal needs the development of smart sensors with on-chip advanced functions and the decrease of manufacturing cost of IRFPA by decreasing the pixel pitch and simplifying the vacuum package. We present in this paper the technology developed by CEA/LETI and its improvement for being able to designs 384×288 and 160×120 arrays with a pitch of 35 μm. Thermographic application needs high stability infrared detector with a precise determination of the amount of absorbed infrared flux. Hence, infrared detector with internal temperature stabilized shield has been developed and characterized. These results will be presented. To cite this article: J.-L. Tissot, C. R. Physique 4 (2003).     

Caractérisation et modélisation de composants matriciels infrarougeCharacterization and modelling of IR sensors

The objective of this paper is to describe the first behavioural models of cooled (based on HgCdTe photodetectors) infrared sensors which were designed at CEA-LETI/SLIR. In this way, the interest of such an approach in the evaluation and improvement of optronic systems will be shown. The paper first presents the modelling approach (architecture of the models, choice of parameters, tools for modelling and calibration, …). Then models are compared to measurements on real components in order to verify the efficiency of the modelling approach. To cite this article: P. Castelein, C. R. Physique 4 (2003).     

De la microstructure du polymère à ses propriétés rhéologiquesFrom the microstructure of polymers towards their rheological properties

We extend the previous work by Benallal et al. on the relationship between structure and rheological properties of linear polymer melts. The aim of this paper is to quantify the effect of the chemical structure on the viscoelastic properties. We show that these properties are governed by the monomer dimensions and the interaction energy. To cite this article: A. Allal et al., C. R. Physique 3 (2002) 1451–1458.     

Transparent Boundary Conditions for Split-Step Padé Approximations of the One-Way Helmholtz Equation

In this paper, we generalize the nonlocal discrete transparent boundary condition introduced by F. Schmidt and P. Deuflhard (1995, Comput. Math. Appl.29, 53–76) and by F. Schmidt and D. Yevick (1997, J. Comput. Phys.134, 96–107) to propagation methods based on arbitrary Padé approximations of the two-dimensional one-way Helmholtz equation. Our approach leads to a recursive formula for the coefficients appearing in the nonlocal condition, which then yields an unconditionally stable propagation method.     

Un coronographe interférentiel achromatique coaxial

We present a new type of stellar interfero-coronagraph, the ‘CIAXE’, which is a variant of the ‘AIC’, the Achromatic Interfero-Coronagraph. The CIAXE is characterized by a very simple, compact and fully coaxial optical combination. Indeed, contrarily to the classical AIC which has a Michelson interferometer structure, the CIAXE delivers its output beam on the same axis as the input beam. This will ease its insertion in the focal instrumentation of existing telescopes or next generation ones. Such a device could be a step forward in the field of instrumental search for exoplanets. To cite this article: J. Gay et al., C. R. Physique 6 (2005).     

Coherent Raman and Infrared Studies of Sulfur Trioxide

High-resolution (0.001 cm⁻¹) coherent anti-Stokes Raman scattering (CARS) was used to observe the Q-branch structure of the IR-inactive ν₁ symmetric stretching mode of ³²S¹⁶O₃ and its various ¹⁸O isotopomers. The ν₁ spectrum of ³²S¹⁶O₃ reveals two intense Q-branches in the region 1065–1067 cm⁻¹, with surprisingly complex vibrational–rotational structure not resolved in earlier studies. Efforts to simulate this with a simple Fermi-resonance model involving ν₁ and 2ν₄ states do not reproduce the spectral detail, nor do they yield reasonable spectroscopic parameters. A more subtle combination of Fermi resonance and indirect Coriolis interactions with nearby states, 2ν₄(1=0, ±2), ν₂+ν₄(1=±1), 2ν₂(1=0), is suspected and a determination of the location of these coupled states by high-resolution infrared measurements is under way. At medium resolution (0.125 cm⁻¹), the infrared spectra reveal Q-branch features from which approximate band origins are estimated for the ν₂, ν₃, and ν₄ fundamental modes of ³²S¹⁸O₃, ³²S¹⁸O₂¹⁶O, and ³²S¹⁸O¹⁶O₂. These and literature data for ³²S¹⁶O₃ are used to calculate force constants for SO₃ and a comparison is made with similar values for SO₂ and SO. The frequencies and force constants are in excellent agreement with those obtained by Martin in a recent ab initio calculation.     

Jules Horowitz Reactor: a high performance material testing reactor

The physical modelling of materials' behaviour under severe conditions is an indispensable element for developing future fission and fusion systems: screening, design, optimisation, processing, licensing, and lifetime assessment of a new generation of structure materials and fuels, which will withstand high fast neutron flux at high in-service temperatures with the production of elements like helium and hydrogen.JANNUS and other analytical experimental tools are developed for this objective. However, a purely analytical approach is not sufficient: there is a need for flexible experiments integrating higher scales and coupled phenomena and offering high quality measurements; these experiments are performed in material testing reactors (MTR). Moreover, complementary representative experiments are usually performed in prototypes or dedicated facilities such as IFMIF for fusion. Only such a consistent set of tools operating on a wide range of scales, can provide an actual prediction capability. A program such as the development of silicon carbide composites (600–1200 °C) illustrates this multiscale strategy.Facing the long term needs of experimental irradiations and the ageing of present MTRs, it was thought necessary to implement a new generation high performance MTR in Europe for supporting existing and future nuclear reactors. The Jules Horowitz Reactor (JHR) project copes with this context. It is funded by an international consortium and will start operation in 2014. JHR will provide improved performances such as high neutron flux (10¹⁵ n/cm²/s above 0.1 MeV) in representative environments (coolant, pressure, temperature) with online monitoring of experimental parameters (including stress and strain control). Experimental devices designing, such as high dpa and small thermal gradients experiments, is now a key objective requiring a broad collaboration to put together present scientific state of art, end-users requirements and advanced instrumentation. To cite this article: D. Iracane et al., C. R. Physique 9 (2008).     

Accurate Measurement of Small Spin–Spin Couplings in Partially Aligned Molecules Using a Novel J-Mismatch Compensated Spin-State-Selection Filter

The accurate measurement of small spin–spin coupling constants in macromolecules dissolved in a liquid crystalline phase is important in the context of molecular structure investigation by modern liquid state NMR. A new spin-state-selection filter, DIPSAP, is presented with significantly reduced sensitivity to J-mismatch of the filter delays compared to previously proposed pulse sequences. DIPSAP presents an attractive new approach for the accurate measurement of small spin–spin coupling constants in molecules dissolved in anisotropic solution. Application to the measurement of ¹⁵N–¹³C′ and ¹H^N–¹³C′ coupling constants in the peptide planes of ¹³C, ¹⁵N labeled proteins demonstrates the high accuracy obtained by a DIPSAP-based experiment.     

Physics-Based Preconditioning and the Newton–Krylov Method for Non-equilibrium Radiation Diffusion

An algorithm is presented for the solution of the time dependent reaction-diffusion systems which arise in non-equilibrium radiation diffusion applications. This system of nonlinear equations is solved by coupling three numerical methods, Jacobian-free Newton–Krylov, operator splitting, and multigrid linear solvers. An inexact Newton's method is used to solve the system of nonlinear equations. Since building the Jacobian matrix for problems of interest can be challenging, we employ a Jacobian–free implementation of Newton's method, where the action of the Jacobian matrix on a vector is approximated by a first order Taylor series expansion. Preconditioned generalized minimal residual (PGMRES) is the Krylov method used to solve the linear systems that come from the iterations of Newton's method. The preconditioner in this solution method is constructed using a physics-based divide and conquer approach, often referred to as operator splitting. This solution procedure inverts the scalar elliptic systems that make up the preconditioner using simple multigrid methods. The preconditioner also addresses the strong coupling between equations with local 2×2 block solves. The intra-cell coupling is applied after the inter-cell coupling has already been addressed by the elliptic solves. Results are presented using this solution procedure that demonstrate its efficiency while incurring minimal memory requirements.     

Millimeter-Wave Spectroscopy, High-Resolution Infrared Spectrum, ab Initio Calculations, and Molecular Geometry of FPS

The transient thiophosphenous fluoride FPS was produced by pyrolysis of 2.5% F₂PSPF₂ in Ar at 1300–1800°C. High-resolution (≥0.004 cm⁻¹) Fourier transform infrared spectra of the a-type ν₁ and b-type ν₂ bands, centered respectively at 803.249 and 726.268 cm⁻¹, were measured and fitted to rotational and quartic centrifugal distortion parameters. The millimeter-wave spectrum, essentially b-type, was measured between 300 and 370 GHz in the ground state and in the ν₃ excited state for FP³²S and in the ground state for FP³⁴S. The frequencies were fitted to a Watson-type A-reduced Hamiltonian up to sextic distortion terms. High level ab initio calculations with large basis sets were performed on FPS and supported the first identification of its infrared and millimeter wave spectra. The calculated anharmonic force field provided precise ab initio rovibrational α constants which were combined with the experimental molecular parameters to determine an accurate equilibrium structure of the molecule: r_e(PS)=188.86 pm, r_e(PF)=158.70 pm, θ(FPS)=109.28°. The collision-controlled 1/e lifetime measured in a 10-Pa (1 : 20) F₂PSPF₂/Ar mixture was 2 s, more than two orders of magnitude larger than that of FPO under the same experimental conditions.     

X-rays and matter – the basic interactions

In this introductory article we attempt to provide the theoretical basis for developing the interaction between X-rays and matter, so that one can unravel properties of matter by interpretation of X-ray experiments on samples. We emphasize that we are dealing with the basics, which means that we shall limit ourselves to a discussion of the interaction of an X-ray photon with an isolated atom, or rather with a single electron in a Hartree–Fock atom. Subsequent articles in this issue deal with more complicated – and interesting – forms of matter encompassing many atoms or molecules. To cite this article: J. Als-Nielsen, C. R. Physique 9 (2008).     

The interaction between a lightning flash and an aircraft in flight

Roughly speaking, every commercial airliner is struck by lightning once per year. Thus, the lightning strike to aircraft is not uncommon and it poses an appreciable threat to flight safety. The understanding of the lightning strike to aircraft has been greatly enhanced during the last years thanks to a comprehensive analysis of data collected from instrumented aircraft that have been flown into thunderstorm regions. In this article, we will start with the phenomenology of the lightning strike to aircraft and continue with going deeper into the underlying physics of selected processes during the strike. To cite this article: A. Larsson, C. R. Physique 3 (2002) 1423–1444.     

High repetition rate mid-infrared laser source

An efficient, high-power mid-infrared laser source based on ZnGeP₂ (ZGP) optical parametric oscillator (OPO) is presented. Using a Q-switched Ho:YAG laser as the pump source a total output power of 10.6 W was obtained in the 3–5 μm band at 10 kHz and 8.5 W at 20 kHz. The Ho:YAG laser was pumped by two diode-pumped polarization coupled Tm:YLF lasers. Optical-to-optical efficiency achieved is >8.8% (laser-diode 792 nm to mid-IR 3–5 μm). With a commercial PtSi infrared camera (256×256 pixel focal plane array, 24 μm pitch) the pointing stability of Ho pump, signal and idler beam was measured to be better than 30 μrad. Whilst propagating the OPO beams over 100 m, little absorption for the idler beam was observed, resulting in a significant higher peak-to-peak value of ±22%, whereas the peak-to-peak stability of the signal pulses remained unchanged (±13%). To cite this article: M. Schellhorn et al., C. R. Physique 8 (2007).     

Nucleation problems in metallurgy of the solid state: recent developments and open questions

Nucleation processes play a key role in the microstructure evolution of metallic alloys during thermomechanical treatments. These processes can involve phase transformations (such as precipitation) and structural instabilities (such as recrystallisation). Although the word ‘nucleation’ is used in both cases, the situation is profoundly different for precipitation and for recrystallisation on which this article is focussed. In the case of precipitation, species are conserved and the underlying physics is stochastic fluctuations, allowing the apparition of critical germs of the new phase. In the case of recrystallisation, the underlying physical phenomenon is the progressive growth of subgrain structures leading to an unstable configuration, allowing a dislocation free grain to grow at the expense of a dislocated one. The two cases require different types of modelling which are presented in the article. To cite this article: Y. Bréchet, G. Martin, C. R. Physique 7 (2006).     

Measurement of Small One-Bond Proton–Carbon Residual Dipolar Coupling Constants in Partially Oriented C Natural Abundance Oligosaccharide Samples: Analysis of Heteronuclear JCH-Modulated Spectra with the BIRD Inversion Pulse

Two 2D J-modulated HSQC-based experiments were designed for precise determination of small residual dipolar one-bond carbon–proton coupling constants in ¹³C natural abundance carbohydrates. Crucial to the precision of a few hundredths of Hz achieved by these methods was the use of long modulation intervals and BIRD pulses, which acted as semiselective inversion pulses. The BIRD pulses eliminated effective evolution of all but ¹J_CH couplings, resulting in signal modulation that can be described by simple modulation functions. A thorough analysis of such modulation functions for a typical four-spin carbohydrate spin system was performed for both experiments. The results showed that the evolution of the ¹H–¹H and long-range ¹H–¹³C couplings during the BIRD pulses did not necessitate the introduction of more complicated modulation functions. The effects of pulse imperfections were also inspected. While weakly coupled spin systems can be analyzed by simple fitting of cross peak intensities, in strongly coupled spin systems the evolution of the density matrix needs to be considered in order to analyse data accurately. However, if strong coupling effects are modest the errors in coupling constants determined by the “weak coupling” analysis are of similar magnitudes in oriented and isotropic samples and are partially cancelled during dipolar coupling calculation. Simple criteria have been established as to when the strong coupling treatment needs to be invoked.     

Moving Mesh Methods in Multiple Dimensions Based on Harmonic Maps

In practice, there are three types of adaptive methods using the finite element approach, namely the h-method, p-method, and r-method. In the h-method, the overall method contains two parts, a solution algorithm and a mesh selection algorithm. These two parts are independent of each other in the sense that the change of the PDEs will affect the first part only. However, in some of the existing versions of the r-method (also known as the moving mesh method), these two parts are strongly associated with each other and as a result any change of the PDEs will result in the rewriting of the whole code. In this work, we will propose a moving mesh method which also contains two parts, a solution algorithm and a mesh-redistribution algorithm. Our efforts are to keep the advantages of the r-method (e.g., keep the number of nodes unchanged) and of the h-method (e.g., the two parts in the code are independent). A framework for adaptive meshes based on the Hamilton–Schoen–Yau theory was proposed by Dvinsky. In this work, we will extend Dvinsky's method to provide an efficient solver for the mesh-redistribution algorithm. The key idea is to construct the harmonic map between the physical space and a parameter space by an iteration procedure. Each iteration step is to move the mesh closer to the harmonic map. This procedure is simple and easy to program and also enables us to keep the map harmonic even after long times of numerical integration. The numerical schemes are applied to a number of test problems in two dimensions. It is observed that the mesh-redistribution strategy based on the harmonic maps adapts the mesh extremely well to the solution without producing skew elements for multi-dimensional computations.     

The Fe–Cr system: atomistic modelling of thermodynamics and kinetics of phase transformations

To understand the behaviour of irradiated defects and kinetic pathways of micro-structural evolution in Fe–Cr alloys, we use a combination of density functional theory with statistical approaches involving cluster expansions and Monte Carlo simulations. A lowest negative mixing enthalpy is found at 6.25% Cr that is consistent with our DFT prediction of an ordered Fe₁₅Cr structure. At 50% Cr, it is found that the predicted enthalpy of formation is 4 times smaller than that calculated by the CPA approach. Thermodynamic and precipitation properties are then discussed in term of segregation between the Fe₁₅Cr and α^′-Cr phases and of vacancy-mediated kMC simulation. To cite this article: D. Nguyen-Manh et al., C. R. Physique 9 (2008).     

D-branes from matrix factorizations

B-type D-branes can be obtained from matrix factorizations of the Landau–Ginzburg superpotential. We here review this promising approach to learning about the spacetime superpotential of Calabi–Yau compactifications. We discuss the grading of the D-branes, and present applications in two examples: the two-dimensional torus, and the quintic. To cite this article: K. Hori, J. Walcher, C. R. Physique 5 (2004).

Résumé

Les D-branes de type B peuvent être décrites à partir de factorisations matricielles du super-potentiel de Landau–Ginzburg. On revoit ici cette approche prometteuse pour étudier le super-potentiel en espace-temps de compactifications de Calabi–Yau. On discute la graduation des D-branes, et présente deux exemples : le tore en deux dimensions, ainsi que la quintique. Pour citer cet article : K. Hori, J. Walcher, C. R. Physique 5 (2004).