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 Kα 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 Kα photon production reported to date corresponding to a Kα 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.

Dynamic magnetic resonance imaging of the breast: Comparison of gadobutrol vs. Gd-DTPA. / Resonancia magnética dinámica de mama: estudio comparativo de gadobutrol y Gd-DTPA.

OBJECTIVE: To compare the pharmacokinetic profile of gadobutrol versus Gd-DTPA in dynamic contrast-enhanced MRI (DCE-MRI) in patients with breast cancer. Secondary objectives included comparing the safety profiles and diagnostic efficacy of the two contrast agents for detecting additional malignant lesions. MATERIAL AND METHODS: This retrospective observational study included 400 patients with histologically confirmed breast cancer; 200 underwent DCE-MRI with Gd-DTPA (Magnevist®) and 200 underwent DCE-MRI with gadobutrol (Gadovist®). Pharmacokinetic parameters and signal intensity were analyzed in a region of interest placed in the area within the lesion that had greatest signal intensity in postcontrast sequences. We compared the two groups on pharmacokinetic variables (Ktrans, Kep, and Ve), time-signal intensity curves, and the number of additional malignant lesions detected. RESULTS: The relative signal intensity (enhancement) was higher with gadobutrol than with Gd-DTPA. Washout was lower with gadobutrol than with Gd-DTPA (46% vs. 58,29%, respectively; p=0,0323). Values for Ktrans and Kep were higher for gadobutrol (p=0,001). There were no differences in the number of histologically confirmed additional malignant lesions detected (p=0,387). CONCLUSIONS: Relative enhancement is greater with gadobutrol, but washout is more pronounced with Gd-DTPA. The number of additional malignant lesions detected did not differ between the two contrast agents. Both contrasts are safe.

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.

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.

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.

[New approach for determining the damage level of biological tissues using femtosecond laser: advantages and application to corneal surgery]. / Nouvelle approche de détermination du seuil d'endommagement de tissus biologiques par laser femtoseconde: intérêt et application à la chirurgie de la cornée.

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.

Dynamic photolytical actinometry of the vacuum-ultraviolet radiation produced by multichannel surface discharges of submicrosecond duration.

Absolute measurements of the vacuum-ultraviolet (VUV) radiation power produced by a planar broadband optical source of submicrosecond light pulse duration are carried out in the transient regime of formation of a photodissociation (bleaching) wave in a photodecomposing absorptive medium. The source is based on a multichannel surface discharge initiated in ArN(2) gas mixtures on the area of approximately 0.1 m(2). The energetic characteristics of the produced VUV radiation are determined on the basis of spatially and temporally resolved observations of the pulsed photolysis of XeF(2) vapors. It is shown that the photon flux intensity produced by the source within the spectral range of 120-200 nm reaches 1.1 x 10(23) photonscm(2) s corresponding to the effective brightness temperature of discharge plasma of 20 kK and to the intrinsic efficiency of the discharge VUV emission of 3.2%. Numerical simulations of the photolysis process show a rather weak sensitivity of the results to the fraction of discharge radiation emitted into the line spectrum, as well as to the angular distribution of emitted radiation. The spectral band of measurements can be selected according to the choice of parent photodecomposing particles.

[Metaplastic carcinoma of the breast: magnetic resonance and radiophatologic correlation]. / Carcinoma metaplásico de mama: resonancia magnética y correlación radiopatológica.

OBJECTIVES: To review our radiological experience in metaplastic carcinoma together with the clinical and histopathologic findings. METHODS AND MATERIALS: Eight cases of histologically confirmed metaplastic carcinoma of breast were reviewed. Imaging findings from US, mammography and MRI, and immunohistochemistry results from preoperative biopsy were assessed. Conventional prognostic factors, chondral differentiation markers, striated and straight muscle markers, neural markers, cytokeratin, vimentin and intermediate filaments were determined. RESULTS: Eight patients aged ranged from 41-72 years. Metaplastic carcinoma presented as a palpable nodule in five cases, as a nipple retraction in ones case, and was discovered as an incidental mammographic finding in two. Mammographic appearance was a round, high-density nodule, measuring 10-50 mm, with variable margins in seven patients. One had architectural distortion. In three there were calcifications. Skin and nipple retraction appeared in one. On sonographic examination nodules were ill defined and showed low heterogeneous echogenicity. On MRI, T2-weighted images showed a relatively well-defined mass with high signal intensity. In the dynamic study, all showed contrast uptake, with signal-time intensity curves similar to those of infiltrating carcinoma of the breast. Histopathologic study found one squamous-cell, one sarcomatous, three chondroid, one giant-cell, one spindle-cell, and one acantholytic carcinoma, all of which were of high histologic grade. CONCLUSIONS: Metaplastic carcinoma should be included in the differential diagnosis of a nodule presenting with high density and variable margins on mammography, low heterogeneous echogenicity and ill defined margins on sonography, and hyperintense at T2 with malignant enhancement at MR. Immunohistochemical assessment is mandatory for the final diagnosis. The radiologist can suggest this particular subtype of tumour.

[Mediastinal enteric cyst: unusual clinical presentation and histopathology]. / Quiste entérico mediastínico: presentación clínica e histopatología inusuales.

A mediastinal enteric cyst is an uncommon entity which is rare in adults and usually found incidentally. In most cases the lesion is lined by gastrointestinal mucosa, and theories as to the origin of such lesions are diverse. We report an adult case of thoracic enteric cyst that presented with cardiac tamponade and for which histopathological examination revealed the presence of pancreatic tissue. Review of the literature yielded only 1 case of mediastinal enteric cyst with pancreatic tissue.

[Noninvasive diagnosis of posttraumatic thoracic splenosis]. / Diagnóstico no invasivo de la esplenosis torácica postraumática.

Thoracic splenosis is a rare occurrence that has usually been diagnosed by invasive procedures to allow a pathologic diagnosis to be reached. A firm diagnosis can now be made with the help of new, noninvasive imaging techniques. We report the case of a 34-year-old man with a history of severe thoracic-abdominal injury, including rupture of the spleen and left diaphragm. During computed tomography of the thorax related to a different diagnosis, nonspecific nodules were observed, although the patient was asymptomatic. A suspected diagnosis of thoracic splenosis was confirmed by technetium-99 sulfur colloid scintigraphy.

[Surgical treatment for compensatory hyperhidrosis in Adie syndrome]. / Tratamiento quirúrgico de la hiperhidrosis compensadora en el síndrome de Adie.

Ross syndrome is characterized by a triad of tonic pupil, areflexia and segmental hypohidrosis. Hypohidrosis may be accompanied by contralateral hyperhidrosis, probably due to a compensatory mechanism. We report a case of Ross syndrome with socially disabling left-sided hyperhidrosis. Sympathectomy of the second and third thoracic ganglia was performed with satisfactory results. With excellent results in primary hyperhidrosis and very low morbidity, thoracic sympathectomy is the definitive treatment for hyperhidrosis.

Factors related to non-participation in a population-based breast cancer screening programme.

The main objectives were to describe the measures taken by women to detect breast disease prior to invitation to participate in a screening programme for breast cancer, and to identify factors related to non-participation in this programme. A cross-sectional study was designed at the Breast Cancer Early Detection Program of Sabadell-Cerdanyola (BCEDP), using data collected in interviews conducted face to face or over the telephone with 13 760 women participating in the programme and 280 non-participants. A total of 74.2% of the participants versus 70.4% of the non-participants reported having taken measures to detect breast disease, and 71.7% of the participants had undergone mammography versus 69.6% of the non-participants. Of the 10 057 women who had had mammograms, 58% had done so less than 2 years previously. Factors found to be associated to non-participation in the multivariate analysis were: higher level of education, higher occupational skills or working at home, self- or gynaecological examination of breasts, and having received hormone replacement therapy. Higher age group was the only factor that increased the probability of not having undergone mammography previously. Despite the high prevalence of prior measures to detect breast cancer and the similar prevalence between participating and non-participating women, this behaviour is much less prevalent in the group of women 60 years of age or older.

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.