Mid-infrared phase modulation via Stark effect on intersubbandtransitions in GaAs/GaAlAs quantum wells

Mid-infrared (~10 μm) electrorefractive effects of intersubband transitions in step GaAs/GaAlAs quantum wells are experimentally analyzed. A method for studying infrared electrorefraction of a two-dimensional structure via the Stark effect is used. The anomalous dispersion is measured over the entire spectral range of the transition and is found to be consistent with the Kramers-Kronig relations in the case of a Lorentzian absorption shape. A solution of Maxwell's equations in the multiquantum well structure is detailed and leads to a good agreement with experimental data. A standard interferometer and a lock-in technique allow a quasi-direct determination of phase and amplitude modulation with very good sensitivity. A theoretical approach based on a Lorentzian model and the solution of Maxwell's equations for a multiple QW (quantum well) structure agreed well with the data     

Mathematical Modelling of Cation Contamination in a Proton‐exchange Membrane

Transport phenomena in an ion‐exchange membrane containing both H⁺ and K⁺ are described using multicomponent diffusion equations (Stefan–Maxwell). A model is developed for transport through a Nafion 112 membrane in a hydrogen‐pump setup. The model results are analysed to quantify the impact of cation contamination on cell potential. It is shown that limiting current densities can result due to a decrease in proton concentration caused by the build‐up of contaminant ions. An average cation concentration of 30 to 40% is required for appreciable effects to be noticed under typical steady‐state operating conditions.     

Predominant role of peripheral chemoreceptors in the termination of apnea in maturing newborn lambs

Apneas are very common and normal in newborns but may become life threatening if they are not terminated appropriately. The aim of this study in newborn lambs was to investigate the influence on apnea termination of postnatal maturation, peripheral chemoreceptor function, and hypoxia. Apneas were induced by passive hyperventilation at varying inspired O2 fraction levels. The apnea termination threshold PCO2 (PATTCO2) was defined as the arterial PCO2 value at the first breath after the apnea. Three groups of awake intubated lambs were studied: 1) intact lambs tested at both 1 and 15 days of life, 2) intact 1-day-old lambs with central tissue hypoxia induced by CO inhalation, and 3) 1-day-old lambs with carotid body denervation (CBD). In individual lambs and regardless of age and carotid body function, there was a PO2-PCO2 response curve that was a determinant for the termination of an apnea. PATTCO2 invariably increased when arterial PO2 increased, regardless of age. During hypoxia and normoxia, PATTCO2 was significantly lower in 15-day-old lambs compared with 1-day-old lambs. No difference was seen during hyperoxia. PATTCO2 values were shifted to higher levels after carotid body removal. Finally, hypoxia induced by either a low inspired O2 fraction or CO inhalation consistently failed to induce a depressive effect on the PATTCO2 even in CBD lambs. In conclusion, in awake newborn lambs, the PCO2 level for apnea termination changed with postnatal age, and carotid body function was essential in lowering PATTCO2, thus protecting the lambs against prolonged apnea. Furthermore, hypoxia consistently failed to depress the reinitiation of breathing after apnea, even in CBD lambs.     

What is new in pediatric pneumology?

Have been selected for this review: 1) the recent and impressive development of high-resolution and spiral CT scan in pediatric thoracic imaging; 2) the emerging of new and promising therapies for asthma (long acting inhaled beta 2-agonists, leukotriene antagonists, anti-IgE monoclonal antibodies); 3) the multifactorial origin of asthma in childhood; 4) the development of thoracoscopic surgery, a minimal-invasive approach beneficial in numerous circumstances.     

Room temperature observation of mid-infrared inter-subband absorption activated by near-infrared illumination in multiple quantum wells

The authors report the near-infrared optical activation of inter-subband transitions in a 250 period GaAs/Ga/sub 0.75/Al/sub 0.25/As multiple quantum well structure free from intentional doping (undoped). A 0.5% resonant absorption peak around 10.2 mu m has been observed at room temperature under a 320 W/cm/sup 2/ near-infrared illumination at 0.835 mu m.<>     

Modeling and experimental observation of parametric fluorescence inperiodically poled lithium niobate waveguides

We present a theoretical and experimental study of parametric generation in a guided wave quasi-phase-matched configuration. A numerical model taking into account inverted domain shape, electrooptic and photorefractive effects, as well as waveguide profiles allows calculation of the observed phase matching curves. The observed parametric fluorescence efficiencies can be explained by assuming a slight reduction of nonlinear coefficient and/or a partial degradation of the nonlinear grating. Optimization of the grating depth profile would permit room temperature parametric oscillation using pump wavelengths and powers attainable with diode lasers     

Shockley–Read–Hall Lifetime Study and Implication in HgCdTe Photodiodes for IR Detection

The Shockley–Read–Hall (SRH) mechanism might be a limiting factor of an infrared (IR) photodiode's dark current. This limitation is twofold. SRH generation might occur in the depletion region of the photodiode. In that case, the corresponding current is usually limiting the low-temperature dark current. Moreover, SRH generation might also occur in the diffusion volume, close to the space charge region, resulting in an increase of the diffusion dark current, usually limiting the high-temperature behavior of the photodiode. Hence, the determination of the SRH lifetime of IR materials is of first importance and has to be measured (or at least estimated) to define upcoming trends in future high-performance IR detectors. During the last few years, a lot of papers have been published about SRH lifetime in III–V materials (InSb, superlattices, InAsSb) and a few other communications have been more focused on comparing different material systems including III–V and II–VI materials. Those latter communications proposed very long SRH lifetimes (longer than ms) for HgCdTe, instead of the classical 10–100 μs usually admitted until now. This paper aims at investigating this SRH lifetime in HgCdTe based on experimental measurements carried out at the Laboratoire d’électronique des technologies de l’information (LETI) on HgCdTe grown in-house. Direct lifetime measurement (photoconductive or photoluminescence decay) as well as indirect estimations from photodiode dark currents are discussed in order to clarify this question of SRH lifetime and its consequences in upcoming advanced IR detection structures. In the end, it appeared that except for p/n extrinsic heterojunctions (for which the narrow gap depleted volume is not well known), most of the devices tested seemed limited by SRH lifetimes in the 10–100-μs range.     

Evolution of the Sedrun landslide (Graubünden, Switzerland) with ortho-rectified air images

The slope movement at Sedrun (Switzerland) has been studied with ortho-rectified images. Displacement maps compiled for two periods (1973–1990 and 1990–2003), based on a correlation of the aerial images indicate maximum average slope movements of 60 cm/year, similar to those obtained by traditional photogrammetry over the period 1973–1990. The limits of the most active zones determined by image correlation correspond to those obtained by fieldwork. Comparison of the two displacement maps shows an acceleration of the instability of 150% since 1990. This paper demonstrates the value of using more than one technique to help understand the evolution of this long-term instability.