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In human muscle the role of myoglobin (Mb) and its relationship to factors such as muscle perfusion and metabolic capacity are not well understood. We utilized nuclear magnetic resonance (NMR) to simultaneously study the Mb concentration ([Mb]), perfusion, and metabolic characteristics in calf muscles of athletes trained long term for either sprint or endurance running after plantar flexion exercise and cuff ischemia. The acquisitions for 1H assessment of Mb desaturation and concentration, arterial spin labeling measurement of muscle perfusion, and 31P spectroscopy to monitor high-energy phosphate metabolites were interleaved in a 4-T magnet. The endurance-trained runners had a significantly elevated [Mb] (0.28 ± 0.06 vs. 0.20 ± 0.03 mmol/kg). The time constant of creatine rephosphorylation (τPCr), an indicator of oxidative capacity, was both shorter in the endurance-trained group (34 ± 6 vs. 64 ± 20 s) and negatively correlated with [Mb] across all subjects ( r = 0.58). The time to reach maximal perfusion after cuff release was also both shorter in the endurance-trained group (306 ± 74 vs. 560 ± 240 s) and negatively correlated with [Mb] ( r = 0.56). Finally, Mb reoxygenation rate tended to be higher in the endurance-trained group and was positively correlated with τPCr ( r = 0.75). In summary, these NMR data reveal that [Mb] is increased in human muscle with a high oxidative capacity and a highly responsive vasculature, and the rate at which Mb resaturates is well correlated with the rephosphorylation rate of Cr, each of which support a teleological role for Mb in O2 transport within highly oxidative human skeletal muscle.

We address the issue of out-of-plane losses in two-dimensional (2D) photonic crystals (PC) etched through a GaAs monomode waveguide clad with standard GaAlAs alloys. We correlate experimental transmission of PCs with two kinds of loss simulation results. The first kind is 2D and introduces an ad hoc imaginary index in the air holes to account for the losses [see (Benisty et al. Appl. Phys. Lett. 76, 532, 2000)]. The second kind is a novel exact three-dimensional calculation inspired by grating-Fourier analysis that provides quantitatively unprecedented agreement with experimental measurements taking into account hole depth as a limiting parameter. We conclude that, in revision to the conclusions of the above reference, the experimental losses are not the intrinsic ones, being larger by a factor of 5 to 10 due to insufficient hole depth. The transition occurs at a critical etch depth shown to be here around 700 nm. We thus predict, for holes deeper than 700 nm, much improved crystals with very low transmission losses and microresonators with ultra-high quality factors.

Using the concept of generalized Wannier functions, adapted from the electronic theory of solids, we demonstrate for two-dimensional photonic crystals the existence of a localized state basis and we establish an efficient computational method allowing a tight-binding-like parameter free modelization of any dielectric structure deviating from periodicity. Examples of numerical simulations using this formalism, including modal analysis of microcavities and waveguides are presented to prove the ability of this approach to deal accurately with large scale systems and complex structures. A tight-binding version of the transfer matrix method is proposed to describe the transmission and reflection properties of finite samples of photonic crystals.

We report on the first characterisation of the band structure of two-dimensional triangular photonic crystals of air holes in an epitaxial group III nitride film. The structures were fabricated by electron beam lithography and reactive ion-etching.

To optimize the appearance of photonic band gaps in nitrides, we study photonic crystals based on low dielectric constant materials. By calculating the photonic band structures we investigate the gap opening. In the case of microcavities, we have calculated the cavity modes by the plane wave method and a supercell approach. We have classified the modes using group theory. Our results demonstrate that gallery-like modes are more sensitive to a variation of the filling factor.

As a step toward the use of photonic crystals in optoelectronic devices, we present a thorough study of 2-D photonic-crystal mirrors etched into a GaAs-AlGaAs planar waveguide. Fabry-Perot resonators are fabricated to deduce the reflectivity, transmission, losses, as well as the penetration lengths of these mirrors. The guided photoluminescence of InAs quantum dots embedded in GaAs is used to obtain the transmission spectra of these cavities. The varying thickness between the mirrors allows a scan across the whole bandgap spectral range. Quality factors (up to 200) and peak transmissions (up to 0.3) are measured showing that mirrors of four rows of holes have 88% reflectivity, 6% transmission and 6% losses. Losses are also related to a two-dimensional transfer matrix method calculation including a recently introduced scheme to account for losses.

The concept of generalized Wannier functions, adopted from the electronic theory of solids, is used to build a localized representation of electromagnetic waves in dielectric materials. For two-dimensional photonic crystals, we demonstrate the existence of such a localized state basis, and we establish an efficient computational method, allowing a tight-binding-like parameter free modelization of any dielectric structure deviating from periodicity. Numerical simulations of a T-shaped photonic crystal waveguide prove its ability to deal with large-scale systems and complex structures.

The construction of 3D photonic crystals with gaps in the visible or the near-infrared frequency range requires engineering of complex microstructures which are very difficult to realize by etching and micro-fabrication. Consequently, self-ordered systems such as synthetic opals are very promising. Synthetic bare opals are constituted by SiO2 spheres that organize themselves by a sedimentation process in a face centered cubic (fcc) arrangement. Using the plane wave method, we examine the photonic band structures of close-packed opal-based photonic crystals with an SiO2 (n = 1.5) matrix. The incomplete photonic band gaps at the X- and L-points have been studied which correspond to normally incident plane waves onto the (100) and (111) crystal planes. With the transfer matrix method, we model the transmission properties. We find that the incomplete gap at the L-point fully inhibits the transmission of waves propagating in the [111] direction for opal sample thicknesses that are easily obtainable. This property shows that bare opals could be good candidates for complete inhibition of transmission in the near-infrared and visible frequency range for given orientations.

We study the transmission and reflection of electromagnetic waves propagating in bare opal photonic crystals. We find that the incomplete gap at the $L$ point fully inhibits the transmission of waves propagating in the [111] direction for opal sample thicknesses that are easily obtainable. This property shows that bare opals could be good candidates for complete inhibition of transmission in the near-infrared and visible frequency range for given orientations. The dependence of the total reflectance on the angle of incidence has been calculated, and a good agreement has been found with available experimental data. We have also analyzed the modification of the transmission properties of bare opals induced by a sintering process. Our calculation predicts a linear decreasing of $L$-midgap frequency when the filling fraction decreases due to sintering, which is also in accordance with experiments.

Photonic crystals are very promising because they provide the ability to create high performance microcavities with a high quality factor for a small modal volume. These cavity modes are obtained by creating defects in the periodicity and the defect design must be optimized to obtain the highest transmission. We investigate defect properties in the graphite structure by varying the size of some cylinders. Using the Transfer Matrix Method, we calculate the in-plane diffraction of defect rows and show how this diffraction affects the transmission of the cavity mode.

We demonstrate InP-based triangular and hexagonal two-dimensional (2-D) planar photonic bandgap (PGB) crystal-based microcavities, positioned on a suspended membrane. Photoluminescence spectra of the structure clearly show well-resolved cavity modes, whose structure depends on the cavity shape. Q factors from 200 up to at least 900 are derived.

The most promising two-dimensional photonic crystals are the graphite lattice of dielectric rods in air background and the triangular lattice of air holes in dielectric background. In this paper, we compare their convenience in achieving structures which inhibit the propagation of visible electromagnetic waves. For visible waves, etching is difficult because the structure period must be smaller than the light wavelength. Furthermore, the semiconductor materials whose electronic band gap does not absorb any optical waves have little dielectric constant, which reduces photonic band gap widths. We show, using the Plane Wave Method and the Transfer Matrix Method, that the triangular structure is not appropriate because its gap is too narrow and its dimensions are too small for fabrication. On the other hand, wider gaps and larger dimensions that should be etched easily in wide gap semiconductors make graphite a much more suitable structure.

We describe experiments on a quasi-two dimensional (2-D) optical system consisting of a triangular array of air cylinders etched through a laser-like Ga(Al)As waveguiding heterostructure. Such a configuration is shown to yield results very well approximated by the infinite 2-D photonic crystal (PC). We first present a set of measurements of the optical properties (transmission, reflection, and diffraction) of slabs of these photonic crystals, including the case of in-plane Fabry-Perot cavities formed between two such crystals. The measurement method makes use of the guided photoluminescence of embedded quantum wells or InAs quantum dots to generate an internal probe beam. Out-of-plant, scattering losses are evaluated by various means. In a second part, in-plane micrometer-sized photonic boxes bounded by circular trenches or by two-dimensional photonic crystal are probed by exciting spontaneous emission inside them. The high quality factors observed in such photon boxes demonstrate the excellent photon confinement attainable in these systems and allow to access the detail of the modal structure. Last, some perspectives for applications are offered.

A tight-binding model is used to investigate confinement and shape effects on the optical absorption spectrum of CdSe nanocrystals up to 5 nm diam. The effects of size dispersion are studied and we show that to simulate the spectrum of a collection of nanocrystals it is not always sufficient to broaden inhomogeneously the mean diameter cluster spectrum. Our results are compared with calculations based on other methods and show good agreement with experimental data. We have also calculated the absorption spectra of CdSe crystallites with different morphologies: spherical clusters and oblate and prolate elliptic nanocrystals. We have performed a comparison of the energies and absorption bands as a function of the morphological changes and we present a detailed study of the modifications in the features of the optical spectra.

The effects of the inclusion of manganese in small ZnS nanocrystals are investigated. Our calculation is based on a tight-binding model with renormalized parameters similar to those of the defect-molecule approach for substitutional transition-metal ions in semiconductors. The nanocrystals of Mn-doped ZnS were 1.1\char21{}3.6 nm. Their electronic and optical properties differed from bulk ZnS:Mn and ZnS nanocrystals. It is shown that in addition to confinement effects, doping enhances the energy gap.

Leg volume changes were assessed in healthy volunteers by mercury strain gauge postural plethysmography in order to study the effects of different types of physical training on lower limb venous distensibility and emptying. Seven endurance trained subjects (E), seven muscle strength trained subjects (M) and seven sedentary subjects (S) were submitted to a tilt table test. The test measured leg filling volumes FV (ml · 100 ml -1 ) during 30° head-up tilt, half-emptying time T 1/2 (seconds) and venous output at the 6th second of emptying (V0 6 ) (ml · 100 ml -1 · min -1 ) during return to horizontal position. Comparative tests were made using an ANOVA test. Results showed significantly higher values for FV and V06 in E (FV: 3.9 ± 0.2 ml · 100 ml -1 in E vs 2.5±0.2 and 2.2 ±0.2 ml · 100 ml -1 in M and S, respectively; V06: 9.2 ± 1.1 ml · 100 ml -1 · min -1 in E vs 6.9 ± 0.7 and 5.5 ± 0.5 ml · 100 ml -1 · min -1 in M and S, respectively) whereas no significant differences were observed between groups for T 1/2 . M and S had the same physiological responses to orthostatic stress. Endurance training seems to increase lower limb venous distensibility without affecting venous emptying and venous return from the lower limbs. These results suggest that the greater venous distensibility in endurance-trained subjects does not result from alterations of the visco-elastic properties of deep vein walls and that it is probably a physical response to hypervolemia consecutive to chronic aerobic training.

Single-line photonic-crystal waveguides are investigated. Photoluminescence experiments and three-dimensional calculation are performed and allow a clear identification of the guided modes. The propagation properties of the latter (group velocity, losses) are extracted from photoluminescence spectra obtained on closed waveguides which act as linear cavities.

Radiation losses occurring in photonic crystals etched into planar waveguides are analyzed using a first-order perturbation approximation. Assuming the incoherent scattering limit, the model indicates that losses diminish as the cladding index approaches the core index. A simple scheme is devised to include these losses into purely two-dimensional calculations by using an imaginary index. Such calculations are shown to agree with corresponding experimental transmission through near-infrared photonic crystals, reproducing the contrasting behavior of the “dielectric” and “air” band edges.

International audience; A quite large programme on wide-gap II-VI materials has been developed in our group. The aim of this paper is to present this work. The choice of material, ZnSe based, is obviously due to the value of this gap (2.7 eV) at room temperature. This material is the most promising for blue-light-emitting diodes, or devices for non-linear optics applications. This paper will be divided into four parts. In the first one the problem of ZnSe/GaAs obtained by OMCVD will be treated. In particular, the band energy diagram at the interface, and in some cases the appearance of a hole gas in the GaAs side, gives rise to some misinterpretation, concerning the p-type conduction of ZnSe.Also the state of the strain of the ZnSe layer depending on the used substrate, is deduced by the shift of the photoluminescence peak.In the second part we extend our discussion to superlattice ZnSe-ZnTe. By using a simple envelope function model, with a given band offset, the critical thickness of barriers and wells are calculated to obtain an emission in the blue wavelength.In the third part the offset is calculated by a self-consistent tight-binding method for the series of Zn chalcogenides. Then, the electronic structure of ZnTe-CdTe superlattices is calculated. Interface states appear due to strong coupling between light and heavy holes when the tight-binding model is used.

The self-consistent tight-binding description of unstrained and strained heterojunctions has recently provided theoretical values for the offset of the average valence band Δ E av v which agree well with experimental data for III–V and II–VI semiconductor compounds. We present here calculations of Δ E av v in other strained heterojunctions with common anion or cation atoms such as ZnS, ZnSe, ZnTe, HgTe and CdTe. The charge transfer in the interface neighbourhood is taken into account by a self-consistent description using realistic values of the dielectric constant e ( q ). First, we have obtained the hydrostatic deformation potentials. Then the Δ E av v are calculated for different situations which can occur for strained heterojunctions according to the strain is confined (i) to one side of the heterojunction as, for instance, CdTe strained to ZnTe or (ii) to the other side: ZnTe strained to CdTe. Results are discussed and compared with those obtained for similar compounds and also to experimental values.

Using the plane wave method, we study two two-dimensional structures that possess absolute photonic band gaps: the triangular and the graphite photonic crystals. We compare their convenience in achieving photonic crystals which inhibit the propagation of visible electromagnetic waves. We show that this is very difficult to obtain with a triangular structure because its gap is too narrow and its dimensions are too small to be fabricated. On the contrary, wider gaps and larger dimensions that can easily be etched makes graphite a much more appropriate structure.

We experimentally demonstrate the existence of complete photonic band gap in graphite-type photonic crystals, thereby confirming theoretical predictions reported in previous studies. Experiments are performed at microwave frequencies from 27 to 75 GHz using hexagonal lattices of alumina rods. Transmission spectra measured for E (TM) and H (TE) polarizations and for different orientations of the two-dimensional lattice are found to be in excellent agreement with numerical calculations. The complete photonic band gap results from the overlap of E7 and H5 forbidden bands. Attenuations larger than 30 dB are measured for structures comprised of only four rows of alumina rods.

We present a study of the transmission coefficients of two-dimensional photonic band gap materials consisting of dielectric cylinders in graphite arrangement. By the study of the attenuation versus slab thickness, we determine the most efficient graphite configuration. We show how uncoupled modes create opaque regions for plane waves propagating along the Γ-P direction and widen the gap originating from the existence of forbidden photonic bands. Our results demonstrate that graphite structure is a promising geometry yielding an attenuation as strong as triangular structure with greater convenience in the fabrication at the submicronic scale.

This investigation examined the impact of a multistressor situation on salivary immunoglobulin A (sIgA) levels, and incidence of upper respiratory tract infection (URTI) during the French commando training (3 weeks of training followed by a 5-day combat course). For the URTI, the types of symptoms were classified according to the anatomical location of the infection. Saliva samples were collected (8 a.m.) from 21 males [21 (2) years] before entry into the commando training, the morning following the 3 weeks of training, after the 5-day combat course, and after 1 week of recovery. sIgA, protein and cortisol concentrations were measured. Symptoms of URTI were recorded during the study from health logs and medical examinations. After the 3 weeks of training, the sIgA concentration was not changed, although it was reduced after the 5-day course [from 120 (14) mg l(-1) to 71 (9) mg l(-1), P0.01]. It returned to pre-training levels within a week of recovery. The incidence of URTI increased during the trial (chi(2)=53.48; P0.01), but was not related to sIgA. Among the 30 episodes of URTI reported, there were 12 rhino-pharyngitis, 6 bronchitis, 5 tonsillitis, 4 sinusitis and 3 otitis. Cortisol levels were raised after the 3-week training (P0.01), dropping below baseline after the combat course (P0.01). Stressful situations have an adverse effect on mucosal immunity and incidence of URTI. However, the relationship between sIgA and illness remained unclear. The large proportion of rhino-pharyngitis indicated that the nasopharyngeal cavity is at a higher risk of infection.

Periodic dielectric structures have been recently proposed to inhibit spontaneous emission in semiconductors. From this suggestion, the new concepts of photonic band gap and photonic crystal have been developed. Zero-threshold lasers, waveguides, antenna substrates, filters and polarizers are promising applications. We propose a new class of two-dimensional periodic dielectric structures with hexagonal symmetry. We study the gap opening according to whether the dielectric constant of the cylinders is larger or smaller than that of the background. A potential application for the creation of photonic crystals in the optical domain is discussed.

We have studied the transmission ofelectromagnetic waves in opals partially and completely infilled by semiconductor materials. The sintering process used to stabilize opals is found to increase the transmission along the [111] direction. We have shown that for increasing thickns of coating, the L-gap first closes for a small relative coating thickness 4% before to progressively broaden up to 33% of the midgap frequency for complete influling. The second incomplete gap in the [100] is nearly closed for bare and complete opals and reaches its maximum value for an intermediate coating. These results shows that opals could be good candidates for inhibition of transmission for photonic devices.

Photonic crystals in the form of large area thin films consisting of closely packed polymethylmethacrylate beads were sedimented on glass substrates. The high ordering of the opaline films made it possible to observe a number of fine features in the optical diffraction, including Fabry-Perot oscillations of the reflectivity and branching of the angular dispersion of the Bragg resonances with increase of the angle of incidence of the light beam. Results of calculations of the photonic band structure and simulations of the reflectance spectra agree well with experimental observations.

International audience; We report a low temperature and room temperature photoluminescence (PL) study of a series of two-dimensional arrays of holes and pillars in a triangular lattice arrangement, fabricated in a 1.8 mu m thick GaN/sapphire epilayer. The sample was patterned by electron beam lithography and reactive ion etching in a CH4/H-2 plasma. Such structures with periodic variation of the dielectric constant may give rise to photonic crystals that can create a range of forbidden frequencies called a photonic bandgap. We have used the PL peak to evaluate the damage introduced onto the semiconductor by the etching procedure, and to determine the magnitude of the relaxation of the strain in the GaN film. Theoretical computations predict the photonic bandgap positions for future experimental investigations.

We present measurements of two-dimensional photonic crystals in a waveguided geometry, using photoluminescence from emitters inserted in the guiding heterostructure as an internal light source. A complete set of measurements is given, including quantitative evaluation of the transmission, reflection and also diffraction coefficients of the samples. Their behaviour is shown to follow mostly the pure 2D theory. Capitalizing on the measured properties, we fabricated one-dimensional cavities. The cavity modes are probed through transmission measurement. The measured quality factor leads to an estimation of the reflectivity of the mirror of the order of 95%. We also designed and fabricated disk cavities surrounded by circular Bragg mirrors. The resonances are probed by exciting the photoluminescence of quantum dots placed inside the cavity. Resonances with quality factors up to 650 are found corresponding to the confined Quasi-Radial Modes.

Periodic dielectric structures have been recently proposed to inhibit spontaneous emission in semiconductors. From this suggestion, the new concepts of photonic band gaps and photonic crystals have been developed. Zero-threshold lasers, waveguides, and polarizers are promising applications. A new class of two-dimensional periodic dielectric structures with hexagonal symmetry is investigated in order to obtain photonic band gap materials. This set has the hexagonal symmetry and contains, in particular, several structures previously discussed. The photonic band gap structure is related to the basic properties of the materials and some features of the opening of the gaps are explained. By varying the crystal pattern, we show how band gaps common to E and H polarizations appear for a new design of two-dimensional periodic dielectric structures. The dependence of the widths of these gaps with the filling patterns is studied and potential application for the creation of photonic crystals in the optical domain is discussed.

We present a design of two-dimensional periodic dielectric structures that gives rise to absolute band gaps common to E and H polarized waves. This structure is formed by an arrangement of parallel cylindrical rods centered at the vertices of regular hexagons. We show that two absolute band gaps exist for lattices of dielectric rods in air. Potential application of this structure at the submicrometer length scale is discussed.

Bend contours due to upper Laue areas are studied when the electron beam is nearly parallel to a high symmetry crystallographic axis. First, the influence of the divergence of the incident electron beam on the visibility of bend contours is investigated. Then the contrast of these bend contours as a function of thickness is studied experimentally and the main features of the variation of this contrast are explained theoretically. Nous avons etudie les contours d'extinction dus aux zones superieures de Laue, apparaissant au voisinage d'une figure de pole. Nous avons d'abord determine l'influence de l'ouverture du faisceau incident sur la nettete des contours. Nous avons ensuite etudie experimentalement la visibilite de ces contours en fonction de l'epaisseur du cristal et nous avons explique theoriquement les principales caracteristiques de la variation de ce contraste.

Nous avons calcule les fonctions de base (sous forme de combinaisons lineaires symetrisees d'ondes planes et d'orbitales atomiques) pour les differentes representations irreductibles du groupe du vecteur d'onde en quelques points et lignes de symetrie de la premiere zone de Brillouin des cristaux possedant la structure du rutile (D). We have calculated the basis functions (as symmetrized linear combinations of plane waves and atomic orbitals) for the various irreducible representations of the wave vector group in a few symmetry points and lines in the first Brillouin zone of crystals belonging to the rutile structure (D).

On montre que la section efficace de diffusion inelastique a un phonon des neutrons lents par un cristal harmonique est proportionnelle a la partie imaginaire de la fonction de Green du crystal, telle quelle a ete definie par Montroll et Potts. On utilise cette relation pour calculer la section efficace pour un cristal contenant des defauts ponctuels.

On etudie les proprietes d'absorption optique et electronique des puits quantiques de GaSb/AlSb. On se place dans le cadre de l'approche de la fonction enveloppe multibande et en considerant la valeur de la discontinuite de la bande de valence qui a ete recemment proposee. Le desaccord du reseau modifie fortement la dispersion de la sous-bande de valence. On etudie aussi les effets d'une contrainte uniaxiale externe

We present quantitative measurements of the interaction between a guided optical wave and a two-dimensional photonic crystal using spontaneous emission of the material as an internal point source. This is the first analysis at near-infrared wavelengths where transmission, reflection, and inplane diffraction are quantified at the same time. Low transmission coincides with high reflection or in-plane diffraction, indicating that the light remains guided upon interaction. Also, good qualitative agreement is found with a two-dimensional simulation based on the transfer matrix method. [S0031-9007(97)04591-2]

We report on the measurement of the diffraction efficiency of two-dimensional photonic-bandgap lattices consisting of a triangular array of circular air holes etched in a semiconductor waveguide. We use the spontaneous emission of the material as an internal point source. Combined with previous reflectivity and transmission measurements, the diffraction data allow us to assess the total amount of out-of-plane losses experienced by a guided wave traversing the dielectric lattice, as a function of the lattice pitch. We found that these losses are particularly weak for some range of parameters, especially in the photonic bandgap of interest. We discuss the reasons why they can be substantial with other parameters.

ZnSe and ZnTe single-crystal layers have been grown onto (100) GaAs substrates by low-pressure metalorganic vapor-phase epitaxy (LP-MOVPE) using the triethylamine-dimethylzinc adduct [DMZn(NEt3)] as the zinc precursor. The selenium and tellurium precursors were H2Se (5% in H2) and di-isopropyltellurium (DiPTe), respectively. These two semiconductors have been grown with different VI/II molar ratios, at different growth temperatures, and with an overall growth pressure ranging from 40 to 400 Torr. Optimal growth parameters have been determined by optical means for the two materials. This information was then used to grow ZnTe/ZnSe strained-layer superlattices. We have studied structures grown on both ZnSe and ZnTe relaxed buffer layers which display a drastic dependence of the Stokes shift between photoluminescence and the optical bandgap on the nature of the buffer layer. Growth interruptions have been used to optimize the optical properties of the superlattices. Theoretical modeling of superlattice band structures has been performed using results of optical and structural characterizations. Observations of zone center transitions as well as excitons associated with the miniband dispersion of the superlattices are reported, in agreement with the theoretical calculation.

InAs monolayers and submonolayers have been introduced by means of molecular beam epitaxy in AlxGa1−xAs structures. Our photoluminescence and photoluminescence excitation measurements represent the first results on heterostructures with In sheets in AlxGa1−xAs. It is argued that these results together with their tight‐binding modeling here presented provide a valid framework to implement a new class of heterostructures based on engineered deep centers.