Demonstration of a Circularly Polarized Plasma-Based Soft-X-Ray Laser.

We report the first experimental demonstration of a laser-driven circularly polarized soft-x-ray laser chain. It has been achieved by seeding a 32.8 nm Kr ix plasma amplifier with a high-order harmonic beam, which has been circularly polarized using a four-reflector polarizer. Our measurements testify that the amplified radiation maintains the initial polarization of the seed pulse in good agreement with our Maxwell-Bloch modeling. The resulting fully circular soft-x-ray laser beam exhibits a Gaussian profile and yields about 10^{10} photons per shot, fulfilling the requirements for laboratory-scale photon-demanding application experiments.

Towards enabling femtosecond helicity-dependent spectroscopy with high-harmonic sources.

Recent advances in high-harmonic generation gave rise to soft X-ray pulses with higher intensity, shorter duration and higher photon energy. One of the remaining shortages of this source is its restriction to linear polarization, since the yield of generation of elliptically polarized high harmonics has been low so far. We here show how this limitation is overcome by using a cross-polarized two-colour laser field. With this simple technique, we reach high degrees of ellipticity (up to 75%) with efficiencies similar to classically generated linearly polarized harmonics. To demonstrate these features and to prove the capacity of our source for applications, we measure the X-ray magnetic circular dichroism (XMCD) effect of nickel at the M2,3 absorption edge around 67 eV. There results open up the way towards femtosecond time-resolved experiments using high harmonics exploiting the powerful element-sensitive XMCD effect and resolving the ultrafast magnetization dynamics of individual components in complex materials.

Impact of wave front and coherence optimization in coherent diffractive imaging.

We present single shot nanoscale imaging using a table-top femtosecond soft X-ray laser harmonic source at a wavelength of 32 nm. We show that the phase retrieval process in coherent diffractive imaging critically depends on beam quality. Coherence and image fidelity are measured from single-shot coherent diffraction patterns of isolated nano-patterned slits. Impact of flux, wave front and coherence of the soft X-ray beam on the phase retrieval process and the image quality are discussed. After beam improvements, a final image reconstruction is presented with a spatial resolution of 78 nm (half period) in a single 20 fs laser harmonic shot.

Gain lifetime measurement of a Ni-like Ag soft X-ray laser.

Experimental results of a two-stage Ni-like Ag soft X-ray laser operated in a seed-amplifier configuration are presented. Both targets were pumped applying the double-pulse grazing incidence technique with intrinsic travelling wave excitation. The injection of the seed X-ray laser into the amplifier target was realized by a spherical mirror. The results show amplification of the seed X-ray laser and allow for a direct measurement of the gain lifetime. The experimental configuration is suitable for providing valuable input for computational simulations.

Fourier-limited seeded soft x-ray laser pulse.

We present what we believe to be the first measurement of the spectral properties of a soft x-ray laser seeded by a high-order harmonic beam. Using an interferometric method, the spectral profile of a seeded Ni-like krypton soft x-ray laser (32.8 nm) generated by optical field ionization has been experimentally determined, and the shortest possible pulse duration has been deduced. The source exhibits a Voigt spectral profile with an FWHM of 3.1+/-0.3 mA, leading to a Fourier-transform pulse duration of 4.7 ps. This value is comparable with the upper limit of the soft x-ray pulse duration determined by experimentally investigating the gain dynamics, from which we conclude that the source has reached the Fourier limit. The measured bandwidth is in good agreement with the predictions of a radiative transfer code, including gain line narrowing and saturation rebroadening.

Single-shot diffractive imaging with a table-top femtosecond soft x-ray laser-harmonics source.

Coherent x-ray diffractive imaging is a powerful method for studies on nonperiodic structures on the nanoscale. Access to femtosecond dynamics in major physical, chemical, and biological processes requires single-shot diffraction data. Up to now, this has been limited to intense coherent pulses from a free electron laser. Here we show that laser-driven ultrashort x-ray sources offer a comparatively inexpensive alternative. We present measurements of single-shot diffraction patterns from isolated nano-objects with a single 20 fs pulse from a table-top high-harmonic x-ray laser. Images were reconstructed with a resolution of 119 nm from the single shot and 62 nm from multiple shots.

Non-thermal desorption/ablation of molecular solids induced by ultra-short soft x-ray pulses.

We report the first observation of single-shot soft x-ray laser induced desorption occurring below the ablation threshold in a thin layer of poly (methyl methacrylate)--PMMA. Irradiated by the focused beam from the Free-electron LASer in Hamburg (FLASH) at 21.7 nm, the samples have been investigated by atomic-force microscope (AFM) enabling the visualization of mild surface modifications caused by the desorption. A model describing non-thermal desorption and ablation has been developed and used to analyze single-shot imprints in PMMA. An intermediate regime of materials removal has been found, confirming model predictions. We also report below-threshold multiple-shot desorption of PMMA induced by high-order harmonics (HOH) at 32 nm. Short-time exposure imprints provide sufficient information about transverse beam profile in HOH's tight focus whereas long-time exposed PMMA exhibits radiation-initiated surface ardening making the beam profile measurement infeasible.

Cure of Helicobacter pylori infection in patients with reflux oesophagitis treated with long term omeprazole reverses gastritis without exacerbation of reflux disease: results of a randomised controlled trial.

BACKGROUND: Helicobacter pylori gastritis may progress to glandular atrophy and intestinal metaplasia, conditions that predispose to gastric cancer. Profound suppression of gastric acid is associated with increased severity of H pylori gastritis. This prospective randomised study aimed to investigate whether H pylori eradication can influence gastritis and its sequelae during long term omeprazole therapy for gastro-oesophageal reflux disease (GORD). METHODS: A total of 231 H pylori positive GORD patients who had been treated for > or =12 months with omeprazole maintenance therapy (OM) were randomised to either continuation of OM (OM only; n = 120) or OM plus a one week course of omeprazole, amoxycillin, and clarithromycin (OM triple; n = 111). Endoscopy with standardised biopsy sampling as well as symptom evaluation were performed at baseline and after one and two years. Gastritis was assessed according to the Sydney classification system for activity, inflammation, atrophy, intestinal metaplasia, and H pylori density. RESULTS: Corpus gastritis activity at entry was moderate or severe in 50% and 55% of the OM only and OM triple groups, respectively. In the OM triple group, H pylori was eradicated in 90 (88%) patients, and activity and inflammation decreased substantially in both the antrum and corpus (p<0.001, baseline v two years). Atrophic gastritis also improved in the corpus (p<0.001) but not in the antrum. In the 83 OM only patients with continuing infection, there was no change in antral and corpus gastritis activity or atrophy, but inflammation increased (p<0.01). H pylori eradication did not alter the dose of omeprazole required, or reflux symptoms. CONCLUSIONS: Most H pylori positive GORD patients have a corpus predominant pangastritis during omeprazole maintenance therapy. Eradication of H pylori eliminates gastric mucosal inflammation and induces regression of corpus glandular atrophy. H pylori eradication did not worsen reflux disease or lead to a need for increased omeprazole maintenance dose. We therefore recommend eradication of H pylori in GORD patients receiving long term acid suppression.

[Protective effect of appendectomy on the development of ulcerative colitis. A case-control study]. / Effet protecteur de l'appendicectomie contre la rectocolite hémorragique.

AIMS: To examine by a case-control study the relationship between appendectomy and subsequent ulcerative colitis development in a French population. METHODS: A total of 150 patients with ulcerative colitis were matched for age (+/- 5 years) and sex, with 150 controls recruited in a preventive medicine center. The following data were collected from medical records and by standardised questionnaire in consultation or by phone: appendectomy and tonsillectomy before the onset of ulcerative colitis, smoking habits and area of residence. RESULTS: The rate of previous appendectomy in patients with ulcerative colitis was 8% (12/150) compared with 30.6% (46/150) in the control group (P=0.001). There was no significant association between ulcerative colitis and tonsillectomy (25.3 and 27.3% in the control and the ulcerative colitis groups, respectively). Smoking was more frequent in the control group (36%) than in the ulcerative colitis group (25.3%) but the difference was not significant (P=0.07). In multivariate analysis, the risk of developing ulcerative colitis was significantly lower after previous appendectomy (odds ratio=0.26; 95% confidence interval: 0.13-0.55; P=7 x 10(-4)). CONCLUSION: Our study confirms the inverse association between appendectomy and subsequent ulcerative colitis, in a French population, after adjusting on smoking.

Neonlike iron x-ray laser: population kinetics and radiative transfer.

In this work, we present collisional-radiative calculations for neonlike iron x-ray lasers. These calculations show the importance of the interaction between the x-ray laser beam and the amplifying medium, which is taken into account in the paraxial Maxwell-Bloch approach. Our calculations are in better agreement with a recent experiment (a prepulse plus two main pulses) on the 3p-3s 0-1 line, than the code EHYBRID which ignores the above interaction. Saturation is attained for plasma lengths near 1 cm, and the calculated effective gain agrees with the experimental value, at least for the first main pulse.

Bleeding reflux esophagitis: a prospective 1-year study in a university hospital.

OBJECTIVES: The prevalence of bleeding from reflux esophagitis has not been studied. The aim of the study was to evaluate the 1-yr prevalence of bleeding from reflux esophagitis, as well as the independent factors associated with bleeding. METHODS: All patients with reflux esophagitis diagnosed with upper digestive tract endoscopy in Reims Hospital in 1996 were included. Studied parameters were prospectively recorded and compared between patients with bleeding and nonbleeding reflux esophagitis. RESULTS: Endoscopy was performed in 1983 patients of whom 219 (11.0%) had overt upper digestive tract hemorrhage. Reflux esophagitis was the cause of bleeding in 32 patients (14.6%). Reflux esophagitis was diagnosed in 391 patients during the same period of time. Bleeding reflux esophagitis accounted for 8.2% of them. Independent factors associated with bleeding were grade 3 or 4 (Savary-Miller) esophagitis (odds ratio [OR]: 25.5, 95% confidence interval [CI]: 9.6-67.9), cirrhosis (OR: 5.7, 95% CI: 1.7-18.9), Eastern Cooperative Oncology Group performance status > or = 3 (OR: 4.6, 95% CI: 1.5-14.2), and anticoagulant therapy (OR: 3.9, 95% CI: 1.2-12.5). A history of reflux esophagitis or heartburn was noted in only 28.1% or 37.5% of the patients with bleeding reflux esophagitis, respectively. CONCLUSIONS: In this population of patients with reflux esophagitis, the prevalence of bleeding esophagitis was high (8.2%). Bleeding esophagitis occurred primarily in patients with severe esophagitis and was the revealing clinical form of gastroesophageal reflux disease in the majority of cases, suggesting that bleeding prevention would hardly be effective.

[Time required for training in colonoscopy. Prospective study of 362 consecutive tests]. / Temps consacré à l'enseignement de la coloscopie. Etude prospective de 362 examens consécutifs.

OBJECTIVES: To assess the time required for training in colonoscopy during one year. MATERIAL AND METHODS: All complete colonoscopies performed under general anesthesia in patients having an intact colon were included. RESULTS: The mean duration of 362 colonoscopies was 23 +/- 12 min. The time required by a senior alone was 19 +/- 9 min (n = 129). There was a significant increase in procedural time (P = 0.001) if a trainee was involved in the case (n = 68) (28 +/- 12 min) and if an assistant carried out the procedure (n = 165) alone (25 +/- 14 min) or with a trainee (27 +/- 9 min). We estimated the time which would have been required for the seniors to perform all the colonoscopies. This time was increased by 24.4% by education of trainees and self-training of assistants. CONCLUSION: The duration of colonoscopy is increased by education, the cost of which should be assessed.

Outcome of erosive/ulcerative reflux oesophagitis in 181 consecutive patients 5 years after diagnosis.

BACKGROUND: Controversy exists as to whether oesophagitis worsens over the long-run and long-term follow-up studies of homogeneous series are scarce. AIMS: This study assessed the level of symptoms and the proportions of patients who underwent anti reflux surgery or were on antisecretory therapy. PATIENTS AND METHODS: Files from 286 patients with a first time diagnosis were retrieved. Outcome data was obtained over the phone from the general practitioners and from the patients. RESULTS: Seventy-five patients had died (26.2%), 2 of whom from anti reflux surgery, and 30 (14.2%) could not be contacted. Of the 181 patients contacted, 18 (9.9%) had undergone anti reflux surgery. Of the 163 remaining patients, 57.7% were no longer on medication (group 1), 31.9% were using antacids, alginate or cisapride (group 2) and 10.4% were on antisecretory therapy (group 3). High initial grades of oesophagitis and older age were linked to antisecretory drug consumption. There were no new cases of haemorrhage or stricture. CONCLUSIONS: Patients in this study showed a low rate of symptomatic relapse and of antisecretory drug requirements and no complications despite having had oesophageal breaks.

Factors influencing corpus argyrophil cell density and hyperplasia in reflux esophagitis patients treated with antisecretory drugs and controls.

A cross sectional study was designed to elucidate the factors influencing the argyrophil cell population in patients with gastroesophageal reflux disease treated with omeprazole (N = 201) or H2-receptor antagonists (N = 118) and in control patients (N = 215). Fasting gastrinemia and Helicobacter pylori serology were determined. Gastritis, Helicobacter pylori infection, and argyrophil cell density and hyperplasia were evaluated in gastric biopsies. The argyrophil cell density was higher in both treatment groups than in controls (P = 0.002 and P = 0.051), whereas argyrophil cell hyperplasia was similar in the three groups. According to multivariate analysis, positive Helicobacter pylori serology was an independent parameter that decreased both density and grade of hyperplasia of argyrophil cells. Female gender and hypergastrinemia were independent factors increasing argyrophil cell density and hyperplasia, whereas antisecretory therapy, age and active gastritis were not. In addition, atrophic gastritis independently increased argyrophil cell hyperplasia. The prevalence of atrophic gastritis was significantly higher in Helicobacter pylori-positive than in negative patients and lower in the patients treated long-term with omeprazole than in the other groups.