Experimental investigation of size broadening of a Kα x-ray source produced by high intensity laser pulses

The size of a hard Kα x-ray source ([Formula: see text] = 17.48 keV) produced by a high intensity femtosecond laser interacting with a solid molybdenum target is experimentally investigated for a wide range of laser intensity (I ~ 1017-2.8 × 1019 W/cm2) and for four values of the temporal contrast ratio (6.7 × 107 < CR < 3.3 × 1010). Results point out the size enlargement of the x-ray source with the increase of laser intensity and with the deterioration of temporal contrast. It amounts up to sixteen times the laser spot size at the highest laser intensity and for the lowest temporal contrast ratio. Using hydrodynamic simulations, we evaluate the density scale length of the pre-plasma L/λ just before the main pulse peak. This allows us to show that a direct correlation with the laser absorption mechanisms is not relevant to explain the large size broadening. By varying the thickness of the molybdenum target down to 4 µm, the impact of hot electron scattering inside the solid is also proved irrelevant to explain the evolution of both the x-ray source size and the Kα photon number. We deduce that the most probable mechanism yielding to the broadening of the source size is linked to the creation of surface electromagnetic fields which confine the hot electrons at the solid surface. This assumption is supported by dedicated experiments where the evolution of the size enlargement of the x-ray source is carefully studied as a function of the laser focal spot size for the highest contrast ratio.

Exploring phase contrast imaging with a laser-based Kα x-ray source up to relativistic laser intensity

This study explores the ability of a hard Kα x-ray source (17.48 keV) produced by a 10 TW class laser system operated at high temporal contrast ratio and high repetition rate for phase contrast imaging. For demonstration, a parametric study based on a known object (PET films) shows clear evidence of feasibility of phase contrast imaging over a large range of laser intensity on target (from ~1017 W/cm2 to 7.0 × 1018 W/cm2). To highlight this result, a comparison of raw phase contrast and retrieved phase images of a biological object (a wasp) is done at different laser intensities below the relativistic intensity regime and up to 1.3 × 1019 W/cm2. This brings out attractive imaging strategies by selecting suitable laser intensity for optimizing either high spatial resolution and high quality of image or short acquisition time.

Truncated Gaussian-Bessel beams for short-pulse processing of small-aspect-ratio micro-channels in dielectrics

In order to control the length of micro-channels ablated at the surface of dielectrics, we use annular filtering apertures for tailoring the depth of focus of micrometric Gaussian-Bessel beams. We identify experimentally and numerically the appropriate beam truncation that promotes a smooth axial distribution of intensity with a small elongation, suitable for processing micro-channels of small aspect ratio. Single-shot channel fabrication is demonstrated on the front surface of a fused silica sample, with sub-micron diameter, high-quality opening, and depth of few micrometers, using 1 ps low-energy (< 0.45 µJ) pulse. Finally, we realize 10 × 10 matrices of densely packed channels with aspect ratio ~5 and a spatial period down to 1.5 μm, as a prospective demonstration of direct laser fabrication of 2D photonic-crystal structures.

High photon flux Kα Mo x-ray source driven by a multi-terawatt femtosecond laser at 100 Hz

We develop a pulsed hard x-ray K_α source at 17.4 keV produced by the interaction of a multi-terawatt peak power infrared femtosecond laser pulse with a thick molybdenum (Mo) target at a 100 Hz repetition rate. We measure the highest Mo K_α photon production reported to date corresponding to a K_α photon flux of 1×10¹¹  ph/(sr·s) and an estimated peak brightness of ∼2.5×10¹⁷  ph/(s·mm²·mrad²(0.1% bandwidth)) at ∼5×10¹⁸  W/cm² driving laser intensity.

Impact of the pulse contrast ratio on molybdenum Kα generation by ultrahigh intensity femtosecond laser solid interaction

We present an extended experimental study of the absolute yield of Kα x-ray source (17.48 keV) produced by interaction of an ultrahigh intensity femtosecond laser with solid Mo target for temporal contrast ratios in the range of 1.7 × 107-3.3 × 109 and on three decades of intensity 1016-1019  W/cm². We demonstrate that for intensity I ≥ 2 × 1018  W/cm² Kα x-ray emission is independent of the value of contrast ratio. In addition, no saturation of the Kα photon number is measured and a value of ~2 × 1010 photons/sr/s is obtained at 10 Hz and I ~1019  W/cm². Furthermore, Kα energy conversion efficiency reaches the same high plateau equal to ~2 × 10-4 at I = 1019  W/cm² for all the studied contrast ratios. This original result suggests that relativistic J × B heating becomes dominant in these operating conditions which is supposed to be insensitive to the electron density gradient scale length L/λ. Finally, an additional experimental study performed by changing the angle of incidence of the laser beam onto the solid target highlights a clear signature of the interplay between collisionless absorption mechanisms depending on the contrast ratio and intensity.

Identification of dengue type 2 virus in febrile travellers returning from Burkina Faso to France, related to an ongoing outbreak, October to November 2016

Dengue fever is rarely reported in travellers returning from Africa. We report two cases of dengue fever in travellers returning from Burkina Faso to France. One of them presented a severe dengue fever with ALT > 1,000 IU/L and pericarditis. Serotype 2 was identified. The cases reflect a large ongoing outbreak with over 1,000 reported cases between August and November in the capital city. Clinicians should consider dengue fever in malaria-negative febrile travellers returning from Africa.

Laser-synthesized oxide-passivated bright Si quantum dots for bioimaging

Crystalline silicon (Si) nanoparticles present an extremely promising object for bioimaging based on photoluminescence (PL) in the visible and near-infrared spectral regions, but their efficient PL emission in aqueous suspension is typically observed after wet chemistry procedures leading to residual toxicity issues. Here, we introduce ultrapure laser-synthesized Si-based quantum dots (QDs), which are water-dispersible and exhibit bright exciton PL in the window of relative tissue transparency near 800 nm. Based on the laser ablation of crystalline Si targets in gaseous helium, followed by ultrasound-assisted dispersion of the deposited films in physiological saline, the proposed method avoids any toxic by-products during the synthesis. We demonstrate efficient contrast of the Si QDs in living cells by following the exciton PL. We also show that the prepared QDs do not provoke any cytoxicity effects while penetrating into the cells and efficiently accumulating near the cell membrane and in the cytoplasm. Combined with the possibility of enabling parallel therapeutic channels, ultrapure laser-synthesized Si nanostructures present unique object for cancer theranostic applications.

Bulk laser-induced damage threshold of titanium-doped sapphire crystals

The bulk laser-induced damage threshold (LIDT) fluence of Ti:sapphire is determined under single-pulse irradiation from the femtosecond to nanosecond temporal regimes in the visible and near-infrared spectral domains. In the range of explored laser conditions, the LIDT fluence increases with both pulse duration and wavelength. The results are also compared to laser interaction with sapphire samples and show an increased resistance to laser damage when the material is doped with Ti(3+) ions. These conclusions are of interest for robust operation of high-peak-power femtosecond Ti:sapphire laser chains.

Monitoring photonic nanojets from microsphere arrays by femtosecond laser ablation of thin films

By comparing finite-difference time-domain near field simulations and femtosecond laser ablation of thin films, we characterize in three dimensional-space photonic nanojets from microsphere arrays. We demonstrate periodic drilling of transparent films with thickness up to 100 nm (onto absorbing substrates) is feasible with 1-microm diameter silica spheres. Working with larger polystyrene spheres, the apparent increase of the propagation length of the photonic nanojets makes possible to drill films as thick as 500 nm. Interestingly, the lateral width of the produced craters can be maintained below 400 nm evidencing the low divergence of the nanojets. For backside illumination of the arrays, the ablation features are located at the top of the microspheres. We reveal field enhancements in and out the spheres as well as laser energy confinement at the particle substrate interface. The wide variety of features observed in the experiments open routes to fabricating nanomaterials.

Pulsed Laser Deposition of Si Nanocluster Films

Reactive laser ablation of Si targets by ArF* excimer laser (wavelength 193 nm, pulse width 15 ns (FWHM)) was performed in He, Ar or O2 0.05-1 Torr atmospheres and led to Si-SiOx nanocluster thin film formation within laser-induced plasma plume. Optical spectroscopy and optical Time-of-Flight (TOF) measurements were carried out during ablation-deposition experiments. A number of large weak emission bands in blue and green-yellow spectral branches were observed both in inert gases and in oxygen ambient atmospheres and attributed to the emission from excited nanoparticles in the plasma plume. TOF measurements proved a different spatio-temporal evolution of this emission compare to the emission of monoatomic particles. The films exhibit photoluminescence bands in the UV region (around 290 nm and between 310-370 nm), in the blue (between 420 and 500 nm), and in the green-yellow (at 520-560 nm). The relative intensities of the luminescence bands depend on the average cluster size, which is determined by preparation conditions (nature and pressure of the ambient gas, laser fluence).

Surface ablation of corneal stroma with few-cycle laser pulses at 800 nm

We report measurements of crater diameter and surface ablation threshold as a function of laser fluence in porcine corneal stroma and fused silica with pulse durations of 7 fs (2.7 optical cycles), 30 fs and 100 fs at 800 nm. For laser pulses with Gaussian radial intensity profile, we show experimentally that the square of the crater diameter is a linear function of the logarithm of the fluence in fused silica, while it is closer to a linear function of the fluence in corneal stroma. Extrapolating these relations to zero diameter indicates that for both media the minimum fluence required for surface ablation is reduced with shorter pulse duration. A simple theoretical model suggests that this effect is due to a more significant contribution of photoionization as the laser pulse duration shortens.

[New approach for determining the damage level of biological tissues using femtosecond laser: advantages and application to corneal surgery]

INTRODUCTION

Optimization of femtosecond laser characteristics in corneal surgery is still needed to improve clinical results. In this study, we describe an original characterization technique able to measure laser damage of corneal tissues precisely and to provide complementary physical results on the laser-matter interaction.

METHOD

A femtosecond laser was used to damage corneas not suitable for graft. The epithelium and the Bowman layer are exposed to a set of different single-shot fixed laser fluences. Optical microscopy can determine the probability of laser damage on the corneal surface. The high damage threshold (minimum fluence systematically damaging the cornea) roughly fixes the operating laser fluence conditions, while the low damage threshold sets the maximum laser fluence level preserving tissue integrity (safety level).

RESULTS

We precisely evaluate the damage fluence threshold of a tissue, using a statistical approach coupled with optical microscopy analysis. This technique gives essential information on laser-tissue interaction with a high rate of confidence. For corneal epithelium and the Bowman layer, we determine the maximum laser fluence level preserving tissue integrity (safety level) and the minimum fluence level systematically damaging the tissue. High and low threshold fluences of epithelium and the Bowman layers are (5.6 ± 0.4 J/cm(2); 2.7 ± 0.1 J/cm(2)), and (7.1 ± 1.1 J/cm(2); 3.4 ± 0.1 J/cm(2)), respectively.

CONCLUSION

These data constitute determinant parameters for clinical applications, since they determine a working window providing the minimal effective irradiation dose that is mandatory for the development of high-quality laser-cutting surgery processes with minimized side effects.

Nanofabrication with pulsed lasers

An overview of pulsed laser-assisted methods for nanofabrication, which are currently developed in our Institute (LP3), is presented. The methods compass a variety of possibilities for material nanostructuring offered by laser-matter interactions and imply either the nanostructuring of the laser-illuminated surface itself, as in cases of direct laser ablation or laser plasma-assisted treatment of semiconductors to form light-absorbing and light-emitting nano-architectures, as well as periodic nanoarrays, or laser-assisted production of nanoclusters and their controlled growth in gaseous or liquid medium to form nanostructured films or colloidal nanoparticles. Nanomaterials synthesized by laser-assisted methods have a variety of unique properties, not reproducible by any other route, and are of importance for photovoltaics, optoelectronics, biological sensing, imaging and therapeutics.

Clinical experience with the new manual and automated large core biopsy systems based on a rotational cutting on a helix

1550

Background: Survival from breast cancer has increased significantly in recent years mainly as a result from better imaging techniques, earlier detection and improved tissue sampling. Newer technologies should improve existing biopsies because major drawbacks, including tumor cell displacement, preclude women and physicians to biopsy suspect lesions. A new large core biopsy device with a direct frontal approach, lesser side effects, less sampling needs, lower costs and improved yields has been evaluated in clinical practice. Methods: The results of 70 subsequent transdermal biopsies with rotational cutting on a helix are evaluated with regard to quality of the sample, patient satisfaction and completeness of diagnosis. The patients with a suspect lesion in the breast are selected in an oncological practice. Malignancy was verified by subsequent excision of the lesion. Attention was given to tumor cell displacement. Benign disease was verified by the subsequent clinical course. Results: In 69 patients at least one high quality sample with an average length of 1.8 cm and 0.3 cm diameter could be obtained. One patient refused the procedure. The average number of biopsy cores needed to obtain a reliable diagnosis was 1.5 (mininum 1 - maximum 5). No complication was noted with regard to pain, hemorrhagy, infection or other wound problems. 64 patients quoted the procedure as relative pain free. In 69 patients the diagnosis was complete with regard to the diagnosis of malignancy or benign disease. No destruction, biopsy artefacts or cell displacement was noted on histopathology. In all diagnoses with malignancy the grade of the tumor could be reliably given as well as steroid receptor content and HER2 immunohistochemistry. FISH-HER2 tests were possible in all HER2 positive tumors. Automated biopsies with vacuumassistance had slightly larger samples compared to the manual technique. Conclusions: The new large core biopsy technique with a rotational cutting on a helix performs well in clinical practice. All developmental goals with regard to quality of sample, patient satisfaction and cost price per biopsy have been met. Large core biopsies are now available for a larger population of women at risk for breast cancer with less risk of complication.

No significant financial relationships to disclose.

Surface fluorescence resonance energy transfer studies on interfacial adsorption of Thermomyces (humicola) lanuginosa lipase, using monomolecular films of cis-parinaric acid

The fluorescence resonance energy transfer (FRET) technique was adapted to study the process whereby lipase is adsorbed to monomolecular lipid films spread at the air-water interface. When cis-parinaric acid (cis-PnA) was spread over an aqueous subphase before the injection of sodium taurodeoxycholate (NaTDC) and Thermomyces lanuginosa lipase (TLL), no FRET was observed. Under these conditions, no adsorption of TLL was detected using an ELISA. In contrast, FRET occurred when cis-PnA was spread over an aqueous subphase containing NaTDC and TLL. The FRET signals observed were attributed to the interactions between the adsorbed TLL and the cis-PnA monomolecular films. Comparisons between the fluorescence emission spectra corresponding to the bulk phase and the aspirated film, in the presence and absence of TLL, showed that cis-PnA was undetectable in the bulk phase. We concluded that the FRET originated from the interface and not from the bulk phase. Using surface FRET, we estimated that the surface excess of the catalytically inactive mutant, TLL(S146A), was 1.6 higher than that present in the wild-type TLL. This finding is in agreement with independent measurements of the surface excess of TLL and TLL(S146A) on monomolecular films of cis-PnA.

Simple Method to Generate Nanosecond UV Pulse Trains

By use of a self-seeding technique, energetic nanosecond UV pulse trains of adjustable characteristics (number of pulses, pulse energy, interpulse delay) can be easily produced from an oscillator-amplifier XeCl laser system.

Modeling of gas dynamics for a laser-generated plasma: propagation into low-pressure gases

The physical phenomena involved during three-dimensional axisymmetric laser-induced plasma expansion into background gas are numerically studied. For this purpose, a multispecies hydrodynamic model is developed which considers the effects of mass and ambipolar diffusions, thermal conduction, viscosity, and nonequilibrium conditions for ionization. This model is applied to describe quantitatively the Si plasma plume expansion into Ar or He gases. It is shown that the mechanism of plasma expansion depends critically on both the pressure and mass of the background gas. The shock front expansion is found to be strongly correlated with ion dynamics. A pronounced difference between heavy-particle and electron temperatures indicates a persistent lack of equilibrium between the heavy particle and the electron in the plasma plume expansion. The Si atoms of the rarefied plume are essentially driven by the backward-moving background gas as a result of a mass diffusion process. It is also noted that the diffusion processes are only important in the last expansion stage, and are less significant in the first stage. Therefore, it is shown that a computation which does not include diffusion effects (Euler equations) can adequately describe only the earliest stage of plasma expansion into background gas. The ability of the Navier-Stokes hydrodynamic multispecies model to predict the key role of the background gas type (Ar, He) and pressure is demonstrated.

[Lupus anticoagulant: complete automation (ACL-Futura) and diagnostic algorithm]

PURPOSE

The technical and clinical evaluation of a new laboratory profile with six tests, for the realization of the assay called "lupic anticoagulant" with the help of ACL-Futura analyzer (Intrumentation Laboratory).

RESULTS

The within-between day imprecision of the tests that compose the profile: APTT-Diluted, APTT-D Mix, LacScreen, LacScreen Mix, LacConfirm and LacConfirm Mix, are between 2.87%-11.61% with controls, this imprecision is lowest with patients. A study of bilirrubin and lipemia interferences is presented. The practicability study present the technical, time consuming difficulty, and shows that the cost of the screening test is about 1136 ptas (6.83 euros) and with the confirmative test is 2766 ptas (16.62 euros). The clinical study describes our preliminary results with the application of this new profile for almost 2 years and six clinical cases are presented.

CONCLUSIONS

The good technical and clinical results of the evaluation of the new profile proposed to detect the positive lupic anticoagulant, in addition to the fully automated assay with the ACL-Futura analyzer, validate the whole method to resolve the increased demand of these parameters.

Sexual dimorphism in the maturation of the pituitary-gonadal axis, assessed by GnRH agonist challenge

OBJECTIVE

To assess whether the maturational changes of the pituitary--gonadal axis in a healthy population show gender-specific changes and to establish normative data for the different Tanner stages.

DESIGN

Prospective, cross-sectional study.

METHODS

The GnRH agonist leuprolide acetate (500 microgram) was administered s.c. to 60 boys and 81 girls (age range, 5--17 years). Serum steroids and gonadotropins were determined at 0 and 24 h and at 0, 3 and 24 h after GnRH agonist challenge respectively, whereas IGF-I, IGF-binding protein-1 (IGFBP-1), IGFBP-3 and sex hormone-binding globulin were measured at baseline.

RESULTS

Baseline and peak LH responses to the agonist in late puberty, and basal and peak FSH levels at all Tanner stages, were higher in girls than in boys. Girls showed higher IGF-I levels than boys throughout puberty, sharper decreases in IGFBP-1 and earlier and greater increases in 17-hydroxypregnenolone, dehydroepiandrosterone (DHEA) and DHEA-sulfate. Testosterone responses to the agonist increased during puberty in males, and showed no changes in females. Conversely, estradiol responses rose throughout puberty in females and remained unchanged until late puberty in males.

CONCLUSION

Leuprolide acetate stimulates gonadotropin and gonadal steroid secretion during puberty in both sexes and increases FSH levels in prepubertal girls. Pubertal maturation of gonadotrope function is gender specific, as it appears to involve increases in both the releasable and reserve pools of LH in males, and of LH and FSH in females. The earlier increase in Delta(5)-steroids in girls may suggest a sharper rise in ovarian cytochrome P450c17 activity along the Delta(5)-steroid pathway, while the failure of estradiol to increase in response to leuprolide acetate in early pubertal males suggests a late maturation of aromatase activity.

Primary lymphoma of the breast: MR imaging features. A case report

Primary non-Hodgkin's lymphoma (NHL) of the breast are rare and represent less than 0.6% of all mammary malignancies. Secondary involvement of the breast in patients with diffuse disease occurs more frequently. The radiologic features of breast lymphoma are nonspecific, and the diagnosis is based on histologic criteria. We present the MR-imaging features of a case of primary NHL of the breast.

[Initial evaluation of the ACL-Futura coagulation analyzer]

PURPOSE

The first analytical performance of analyzer ACL-Futura (Instruments Laboratory) is presented.

RESULTS

The analyzer shows an within-between day imprecision with controls, for PT (prothrombin time) of 0.7-8%, APTT (activated partial thromboplastin time) of 0.7-4%, fibrinogen (derived) 2-6%, ATIII (antithrombin III) of 3-9%, with specimens the imprecision is lowest. The linearity and carry-over for all the techniques were studied. An study of medicine interferences (Aspirin and Sintrom) and bilirubin, lipemia was performed. The reference values are presented. We study the practicability of the analyzer: technical difficulty, time consuming, determination cost and the usefulness in the urgency laboratory.

CONCLUSION

These results validate the method to resolve the increased demand of these parameters.

Comparison of in-phase and opposed-phase GRE and conventional SE MR pulse sequences in T1-weighted imaging of liver lesions

PURPOSE

Our goal was to compare in-phase (IP) and opposed-phase (OP) GRE and conventional SE sequences in T1-weighted (T1-W) imaging of the liver and to evaluate chemical shift GRE imaging in characterizing liver/lesions for fat content.

METHOD

IP and OP T1-W GRE with fast low angle shot (FLASH) technique and T1-W SE sequences were compared in 162 patients at 1.0 T. Chemical shift GRE imaging was used to characterize lesions with fat content. Two hundred sixteen lesions were analyzed in three groups of liver: (a) "normal" liver (n = 74 with 110 lesions); (b) cirrhotic liver (n = 76 with 85 lesions); and (c) fatty liver (n = 12 with 21 lesions). Liver/lesion contrast and liver/lesion contrast-to-noise ratio were assessed for lesion detectability. The percentage of signal intensity variation (SIV) between IP and OP images was used to characterize lesions for fat content.

RESULTS

The OP GRE sequence had significantly higher contrast for normal and cirrhotic livers (p < 0.001), and the IP GRE sequence had significantly higher contrast and contrast-to-noise ratio for fatty liver (p < 0.001). There were no significant differences between OP, IP, and T1-W SE imaging in cirrhotic cases for contrast-to-noise ratio (p < 0.28). Chemical shift imaging detected fat in 21 lesions (9.7%, mean SIV, 191.1%) (sensitivity and specificity 100% when compared with fine needle aspiration cytology).

CONCLUSION

OP GRE sequences could replace conventional SE sequences in T1-W imaging in nonfatty livers, whereas in fatty livers, T1-W SE sequences could be obviated, but both OP and IP sequences are necessary. Chemical shift imaging (OP and IP) can be used to accurately characterize lesions for fat content.

[First evaluation of the Variant haemoglobin analyzer (Bio-Rad)]

PURPOSE

The analytical performance of the first automated HPLC analyzer of haemoglobins A2 and Foetal is presented.

RESULTS

The analyzer shows an imprecision within-run between 0.66-2.7% and between-run 1.8-6.44. Correlation index with manual methods were r = 0.965 (p < 0.005) for Hb A2 and r = 0.999 (p < 0.0001) for Foetal Hb and the reference values of an adult population were established; Hb A2 (1.98-2.94%) and Hb F (0-0.95%). Several chromatograms of haemoglobinopathies are presented.

CONCLUSIONS

These results validate the method to resolve the increased demand of these parameters.

Fine needle aspiration of myofibroblastoma of the breast in a man. A report of two cases

The cytopathologic features of fine needle aspiration biopsy of two myofibroblastomas of the breast in men are described. The cytologic findings consisted of monomorphic spindle cells with ovoid, grooved nuclei, isolated or in clusters, with an ill-defined, short fascicular pattern and abundant acellular, myxoid-appearing material. Atypical features were absent. No epithelial elements were present. We emphasize the value of aspiration cytology in association with clinical and mammographic data to establish a definitive diagnosis of this uncommon entity. This benign tumor should be considered in pure spindle cell, nontypical fine needle aspiration biopsy specimens of breast masses with sharp demarcation from the surrounding tissue, especially in men.

Effects of altered thyroid function on histamine levels and mast cell number in neonatal rat brain

The effects of altered thyroid function on the levels of histamine, histidine decarboxylase activity and the number of mast cells were studied in the brain of 5-day-old rats. At this age both brain histamine levels and mast cells number are at a maximum. In addition the major portion of the amine is stored in mast cells and upon subcellular fractionation it sediments in the crude nuclear fraction (P1). Treatments with thyroid hormones or thyrotropic hormone up to 5 days of age leads to a decrease in the histamine levels and mast cells number in the brain, whereas administration of the antithyroid agent 6-n-propyl-2-thiouracil increases both parameters. All treatments affected only the histamine in the P1 fraction and failed to alter the levels of neuronal histamine which is located in the supernatant of P1 (S1). These facts suggest that in neonatal rat thyroid hormones could be involved in the regulation of the levels of brain histamine by regulating the number of brain mast cells.