Spatial Properties of Entangled Two-Photon Absorption.

We experimentally study entangled two-photon absorption in rhodamine 6G as a function of the spatial properties of a high flux of broadband entangled photon pairs. We first demonstrate a key signature dependence of the entangled two-photon absorption rate on the type of entangled pair flux attenuation: linear, when the laser pump power is attenuated, and quadratic, when the pair flux itself experiences linear loss. We then perform a fluorescence-based Z-scan measurement to study the influence of beam waist size on the entangled two-photon absorption process and compare this to classical single- and two-photon absorption processes. We demonstrate that the entangled two-photon absorption shares a beam waist dependence similar to that of classical two-photon absorption. This result presents an additional argument for the wide range of contrasting values of quoted entangled two-photon absorption cross sections of dyes in literature.

Dynamics of the femtosecond laser-triggered spark gap.

We present space and time resolved measurements of the air hydrodynamics induced by femtosecond laser pulse excitation of the air gap between two electrodes at high potential difference. We explore both plasma-based and plasma-free gap excitation. The former uses the plasma left in the wake of femtosecond filamentation, while the latter exploits air heating by multiple-pulse resonant excitation of quantum molecular wavepackets. We find that the cumulative electrode-driven air density depression channel plays the dominant role in the gap evolution leading to breakdown. Femtosecond laser heating serves mainly to initiate the depression channel; the presence of filament plasma only augments the early heating.

Growth arrest specific 1 (Gas1) and glial cell line-derived neurotrophic factor receptor α1 (Gfrα1), two mouse oocyte glycosylphosphatidylinositol-anchored proteins, are involved in fertilisation.

Recently, Juno, the oocyte receptor for Izumo1, a male immunoglobulin, was discovered. Juno is an essential glycosylphosphatidylinositol (GIP)-anchored protein. This result did not exclude the participation of other GIP-anchored proteins in this process. After bibliographic and database searches we selected five GIP-anchored proteins (Cpm, Ephrin-A4, Gas1, Gfra1 and Rgmb) as potential oocyte candidates participating in fertilisation. Western blot and immunofluorescence analyses showed that only three were present on the mouse ovulated oocyte membrane and, of these, only two were clearly involved in the fertilisation process, namely growth arrest specific 1 (Gas1) and glial cell line-derived neurotrophic factor receptor α1 (Gfrα1). This was demonstrated by evaluating oocyte fertilisability after treatment of oocytes with antibodies against the selected proteins, with their respective short interference RNA or both. Gfrα1 and Gas1 seem to be neither redundant nor synergistic. In conclusion, oocyte Gas1 and Gfrα1 are both clearly involved in fertilisation.

Gas-Solid Phase Transition in Laser Multiple Filamentation.

While propagating in transparent media, near-infrared multiterawatt (TW) laser beams break up in a multitude of filaments of typically 100-200 um diameter with peak intensities as high as 10 to 100 TW/cm^{2}. We observe a phase transition at incident beam intensities of 0.4 TW/cm^{2}, where the interaction between filaments induce solidlike two-dimensional crystals with a 2.7 mm lattice constant, independent of the initial beam diameter. Below 0.4 TW/cm^{2}, we evidence a mixed phase state in which some filaments are closely packed in localized clusters, nucleated on inhomogeneities (seeds) in the transverse intensity profile of the beam, and other are sparse with almost no interaction with their neighbors, similar to a gas. This analogy with a thermodynamic gas-solid phase transition is confirmed by calculating the interaction Hamiltonian between neighboring filaments, which takes into account the effect of diffraction, Kerr self-focusing, and plasma generation. The shape of the effective potential is close to a Morse potential with an equilibrium bond length close to the observed value.

Spin-Glass Model Governs Laser Multiple Filamentation.

We show that multiple filamentation patterns in high-power laser beams can be described by means of two statistical physics concepts, namely, self-similarity of the patterns over two nested scales and nearest-neighbor interactions of classical rotators. The resulting lattice spin model perfectly reproduces the evolution of intense laser pulses as simulated by the nonlinear Schrödinger equation, shedding new light on multiple filamentation. As a side benefit, this approach drastically reduces the computing time by 2 orders of magnitude as compared to the standard simulation methods of laser filamentation.

Laser filamentation as a new phase transition universality class.

We show that the onset of laser multiple filamentation can be described as a critical phenomenon that we characterize both experimentally and numerically by measuring a set of seven critical exponents. This phase transition deviates from any existing universality class and offers a unique perspective of conducting two-dimensional experiments of statistical physics at a human scale.

Reversibility of laser filamentation.

We investigate the reversibility of laser filamentation, a self-sustained, non-linear propagation regime including dissipation and time-retarded effects. We show that even losses related to ionization marginally affect the possibility of reverse propagating ultrashort pulses back to the initial conditions, although they make it prone to finite-distance blow-up susceptible to prevent backward propagation.

Mid-infrared laser filamentation in molecular gases.

We observed the filamentation of mid-infrared ultrashort laser pulses (3.9 µm, 80 fs) in molecular gases. It efficiently generates a broadband supercontinuum over two octaves in the 2.5-6 µm spectral range, with a red-shift up to 500 nm due to the Raman effect, which dominates over the blue shift induced by self-steepening and the gas ionization. As a result, the conversion efficiency into the Stokes region (4.3-6 µm) 65% is demonstrated.

High-field quantum calculation reveals time-dependent negative Kerr contribution.

The exact quantum time-dependent optical response of hydrogen under strong-field near-infrared excitation is investigated and compared to the perturbative model widely used for describing the effective atomic polarization induced by intense laser fields. By solving the full 3D time-dependent Schrödinger equation, we exhibit a supplementary, quasi-instantaneous defocusing contribution missing in the weak-field model of polarization. We show that this effect is far from being negligible, in particular when closures of ionization channels occur and stems from the interaction of electrons with their parent ions. It provides an interpretation of the higher-order Kerr effect recently observed in various gases.

[COPD in dairy farmers: screening, characterization and constitution of a cohort. The BALISTIC study]. / BPCO des producteurs laitiers : dépistage, caractérisation et constitution d'une cohorte. Étude BALISTIC.

BACKGROUND: A pilot study from our group suggests that the prevalence of chronic obstructive pulmonary disease (COPD) among dairy farmers is higher than in the general population although dairy workers are less frequently smokers. OBJECTIVES AND METHODS: The study presented here aims at (i) determining the prevalence of COPD in a large and representative population of dairy farmers; (ii) characterizing these patients in terms of smoking habits, dyspnoea, quality of life, lung function, bronchial exhaled nitric oxide, systemic inflammation, arterial stiffness and exercise capacity; (iii) comparing characteristics of dairy farmers' COPD with the characteristics of COPD in patients without any occupational exposure; (iv) identifying the etiological factors of COPD in dairy farmers; and (v) constituting a cohort of COPD patients and control subjects for further longitudinal studies. Two groups of COPD patients (dairy farmers or not) and two groups of controls subjects will be selected among a representative panel of 2000 dairy workers and 2000 subjects without any occupational exposure, all aged 40 to 75 years. EXPECTED RESULTS: A better knowledge of the epidemiology and pathophysiology of COPD in dairy farmers should guide a specific strategy of prevention. The knowledge of the characteristics of COPD occurring in dairy farmers will help to define the therapeutic modalities that might be different compared with the therapeutic recommendations for COPD secondary to tobacco smoking.

[Imaging of male infertility: techniques and results]. / Imagerie de l'hypofertilité masculine : technique et résultats.

Assessment of male infertility includes clinical examination, laboratory tests (semen analysis, hormones dosage) and sonographic examination of the urogenital tract. Male infertility is due to testicular abnormalities (secretory type) or obstructive disorder (excretory type). Imaging should provide accurate definition of anatomical causes of infertility in order to deliver appropriate treatment. Testicular Doppler ultrasound with transrectal ultrasound is the gold standard imaging technique to explore male infertility. MRI, because of its high resolution, provides a multiplanar study especially in congenital and inflammatory abnormalities of the urogenital tract. This pictorial review illustrates the most frequent causes of male infertility.

[Prostatitis and fertility: the biologist's point of view]. / Prostatite, fertilité : le point de vue du biologiste.

There are two leukocytospermia: the leukocytospermia below 10(6) cells/ml comes from the epididymis. It is physiological, improves sperm quality and ART outcomes and therefore must be respected. Leukocytospermia above 10(6) cells/ml are of prostatic origin and reflect a chronic prostatitis. The results of IVF and ICSI with these sperm are always surprisingly improved when compared to those obtained using semen without leukocytes at all. But this improvement is offset by a dramatic increase in the miscarriage rate. Should we treat this leukocytospermia or its cause? A clinical trial is conducted in Cochin hospital with the PHRC Sigma (Male Genital Track Inflammatory Syndrome) that will help us answer this question. It seems, a priori, that it is better to treat the cause and to respect the leukospermia.

[Pre-washing catheter dramatically improves the post intrauterine insemination pregnancy rate]. / Le rinçage des cathéters avant insémination intra-utérine augmente considérablement les taux de grossesses.

OBJECTIVE: To analyze the effectiveness of pre-washing the intrauterine insemination catheters on IUI outcome. PATIENTS AND METHODS: Infertile couples (n=322) involved in a IUI program were included in the study. IUI indications were cervical factors, ovulation dysfunction, cryopreserved semen and unexplained infertility. Every other week for two years, IUI catheters were washed with culture medium prior to intrauterine sperm insemination. RESULT(S): Only the first IUI for each couple were analyzed. Washing the catheter, prior to use, resulted in a 49.7% increase in clinical pregnancy rate (22.0% vs 14.7% P<0.05). This result is observed with fresh sperm (15.7% vs 11.1%) and frozen-thawed sperm as well (31.1% vs 19.8%). The early pregnancy termination rate was similar in all groups. DISCUSSION AND CONCLUSION: Pre-washing the catheter before IUI should be recommended in Good Laboratory Practice Guidelines as it is already the case for embryo transfer catheters. This raises the problem of washing all single-use devices, in contact with gametes or embryos during IVF.

Coherent manipulation of free amino acids fluorescence.

Coherent manipulation of molecular wavepackets in biomolecules might contribute to the quest towards label-free cellular imaging and protein identification. We report the use of optimally tailored UV laser pulses in pump-probe depletion experiments that selectively enhance or decrease fluorescence between two aromatic amino acids: tryptophan (Trp) and tyrosine (Tyr). Selective fluorescence modulation is achieved with a contrast of ~35%. A neat modification of the time-dependent fluorescence depletion signal of Trp is observed, while the Tyr transient trace remains unchanged. The mechanism invoked for explaining the change of the depletion of Trp is a less efficient coupling between the fluorescing state and the higher non-radiative excited states by the optimally shaped pulse, than by the reference pulse.

Ultrafast laser spectroscopy and control of atmospheric aerosols.

We review applications of ultrafast laser pulses for aerosol analysis via linear and non-linear spectroscopy, including the most advanced techniques like coherent control of molecular excited states. We also discuss the capability of such pulses to influence the nucleation of atmospheric aerosols by assisting condensation of water in air.

Modelling of HNO3-mediated laser-induced condensation: a parametric study.

Based on both static (extended Köhler) and dynamic modelling, we investigate the influence of temperature, humidity, HNO(3) initial concentration, as well as of the particle concentration, on the efficiency of HNO(3)-mediated laser-induced condensation. This mechanism is most efficient for low temperatures, high HNO(3) concentration, and relative humidities. It is, however, still active up to 30 °C, down to 70% relative humidity, and below the ppm level of HNO(3). Furthermore, lower particle concentration minimizing the depletion of both HNO(3) and water vapor is more favourable to particle growth.

Field measurements suggest the mechanism of laser-assisted water condensation.

Because of the potential impact on agriculture and other key human activities, efforts have been dedicated to the local control of precipitation. The most common approach consists of dispersing small particles of dry ice, silver iodide, or other salts in the atmosphere. Here we show, using field experiments conducted under various atmospheric conditions, that laser filaments can induce water condensation and fast droplet growth up to several µm in diameter in the atmosphere as soon as the relative humidity exceeds 70%. We propose that this effect relies mainly on photochemical formation of p.p.m.-range concentrations of hygroscopic HNO(3), allowing efficient binary HNO(3)-H(2)O condensation in the laser filaments. Thermodynamic, as well as kinetic, numerical modelling based on this scenario semiquantitatively reproduces the experimental results, suggesting that particle stabilization by HNO(3) has a substantial role in the laser-induced condensation.

Transition from plasma-driven to Kerr-driven laser filamentation.

While filaments are generally interpreted as a dynamic balance between Kerr focusing and plasma defocusing, the role of the higher-order Kerr effect (HOKE) is actively debated as a potentially dominant defocusing contribution to filament stabilization. In a pump-probe experiment supported by numerical simulations, we demonstrate the transition between two distinct filamentation regimes at 800 nm. For long pulses (1.2 ps), the plasma substantially contributes to filamentation, while this contribution vanishes for short pulses (70 fs). These results confirm the occurrence, in adequate conditions, of filamentation driven by the HOKE rather than by plasma.

[ART with sperm donor after intraconjugal ICSI failure]. / Prise en charge en don de sperme après échec(s) d'ICSI intraconjugale.

OBJECTIVES: To evaluate the ART results with sperm donation for couples who do not succeed after IC ICSI treatment for male infertility. PATIENTS AND METHODS: Retrospective study of 71 couples (November 1994-February 2009). Two control populations were determined to analyse this two-steps treatment (IC and sperm donation) based on different criteria such as the date of ICSI, the female age at the time of the first attempt and the male indication. RESULTS: In IC-ICSI, the proportion of azoospermic subjects and/or carrying chromosomal abnormalities was significantly higher in the studied population as compared to control. The fertilization rate (FR) and the embryo quality were significantly lower in the studied population. After donation, 30 couples (42.2%) succeeded in being parents. The donor IA pregnancy rates were similar to those of the control population except for the azoospermic patients with poor results. When IVF/ICSI-D was performed, the pregnancy rates were lower than in the control population. DISCUSSION AND CONCLUSION: Sperm donation constitutes an option for half of the couples initially treated with IC-ICSI for male infertility. For couples who failed in sperm donation, a female implication cannot be excluded, even though not detected.

From higher-order Kerr nonlinearities to quantitative modeling of third and fifth harmonic generation in argon.

The recent measurement of negative higher-order Kerr effect (HOKE) terms in gases has given rise to a controversial debate, fed by its impact on short laser pulse propagation. By comparing the experimentally measured yield of the third and fifth harmonics, with both an analytical and a full comprehensive numerical propagation model, we confirm the absolute and relative values of the reported HOKE indices.