High-contrast 10 fs OPCPA-based front end for multi-PW laser chains.

Applications using multi-PW lasers necessitate high temporal pulse quality with a tremendous contrast ratio (CR). The first crucial prerequisite to achieve multi-PW peak power is the generation of ultrashort pulses with good spectral phase quality. Second, to avoid any deleterious pre-ionization effect on targets, nanosecond contrast better than 1012 is also targeted. In the framework of the Apollon 10 PW French laser program, we present a high-contrast 10 fs front-end design study to inject highly energetic Ti:sapphire PW lasers. The CR has been measured and analyzed in different time ranges highlighting the different major contributions for each scale.

[Changes in the incidence and mortality rates of malignant melanoma in the Seine-Maritime region over a 20-year period]. / Évolution de l'incidence et de la mortalité du mélanome en Seine-Maritime sur une période de 20ans.

BACKGROUND: The aim of this study was to assess changes in the incidence and mortality rates of malignant melanoma (MM) over a 20-year period in a region without a cancer registry. METHODS: All cases of MM studied were collected retrospectively from the databases of six private and three hospital-based histopathology laboratories in the Seine-Maritime region covering three 24-month periods each 10years apart: 1988-1989, 1998-1999 and 2008-2009, The incidence and mortality rates were estimated based on data provided by French National Institute for Statistics and Economic Studies (Insee) and French National Institute of Health and Medical Research (Inserm). RESULTS: Over the 20-year period, the incidence of MM increased from 8.6 to 21.2/100,000inhabitants per year (+147%, P<0.0001) while the mortality rate rose from 1.3 to 2.8/100,000inhabitants per year (+115%, P=0.0003). The incidence of invasive MM increased by +110%, while the incidence of MM in situ increased by +456%. The incidence and overall mortality rate of invasive MM increased particularly during the first 10-year period: +62% (P<0.0001) and +77% (P=0.01) respectively, and to a much lesser extent during the last 10-year period: +30% (P=0.0007) and +22% (P=0.22) respectively. This slowdown in the incidence of invasive MM and in overall mortality rates was even more pronounced in women over the last 10years (+17 and +9%), whereas these rates continued to increase in men (+49% and +35%, respectively). In contrast, the incidence of MM in situ increased above all during this same period (+257%). CONCLUSION: This study shows that while the incidence and mortality rate of invasive MM has increased little over the last 10years in the Seine-Maritime region, the incidence of MM in situ continues to rise sharply.

Phased-array grating compression for high-energy chirped pulse amplification lasers.

The development of phased-array grating compressor is a crucial issue for high-energy, ultra-short pulse petawatt-class lasers. We present a theoretical and experimental analysis of two-grating phasing in a broadband pulse mosaic compressor. The phase defaults induced by misaligned gratings are studied. Monochromatic grating phasing is experimentally achieved with an interferometric technique and pulse compression is demonstrated with a two-phased-array grating system.

High-dynamic-range temporal measurements ofshort pulses amplified by OPCPA.

We report on the first experimental measurement of high-dynamic-range pulse contrast of compressed optical parametric chirped-pulse-amplification (OPCPA) pulses on the picosecond scale. The measured -80-dB OPCPA contrast at 1054 nm agrees well with theoretical predictions and exceeds the estimated and measured levels for comparable amplification in a Ti:sapphire regenerative amplifier by approximately 10 dB. A key to achieving better contrast with OPCPA is the simpler experimental setup that promotes more-efficient coupling of seed pulse energy into the amplification system.

Synthetic aperture compression scheme for a multipetawatt high-energy laser.

High-energy petawatt lasers using the chirped-pulse amplification technique require meter-sized gratings to limit the beam fluence on the surface of the grating. An alternative, studied by many groups, is a mosaic grating consisting of smaller, coherently added gratings. We propose what we believe to be a new compression scheme consisting of beam phasing instead of grating mosaic phasing. This synthetic aperture compression scheme allows us to control the beam thanks to a unique segmented mirror equipped with three degrees of freedom. With this configuration, the beam is divided into small subapertures adapted to the classical grating size. After compression, these subapertures are coherently added before the focusing stage. Therefore the alignment processes are simplified.

A novel model for equine recurrent airway obstruction.

Equine recurrent airway obstruction (RAO; a term combining both chronic obstructive pulmonary disease (COPD) and summer pasture associated obstructive pulmonary disease (SPAOPD)) is one of the most common equine respiratory diseases with up to 50% of horses affected worldwide. The etiopathogenesis of RAO is unknown although pulmonary hypersensitivity to inhaled mold antigens may be involved. Recent work in our laboratory demonstrating elevated levels of IL-4 and IL-13 mRNA in the airways and peripheral blood of horses with RAO is consistent with an atopic component to RAO. Little is known regarding the earliest phases of RAO in horses. Here we describe the development of a novel airway model for equine RAO that utilizes ovalbumin-coated polystyrene beads for airway sensitization and challenge. Aerosol challenge of sensitized ponies with OVA-coated microbeads resulted in decreased airway compliance, increased percentage of lymphocytes and neutrophils in the bronchoalveolar lavage fluid, and evidence of a Th2 cytokine response in the bronchoalveolar cells. These results suggest that this approach may be useful in describing the initial stages of RAO development in the horse.

Single-shot real-time characterization of chirped-pulse amplification systems by spectral phase interferometry for direct electric-field reconstruction.

We characterize chirped-pulse amplification systems by using spectral phase interferometry for direct electric-field reconstruction. For the first time to the authors' knowledge, single-shot real-time operation has been obtained for this technique, leading to a fast and accurate optimization of these systems.

Solitonlike pulse shortening in a femtosecond parametric amplifier.

We demonstrate numerically that simultaneous second-harmonic generation and moderate group-velocity mismatch can lead to spontaneous nonlinear shortening during parametric amplification. As an experimental proof we present the results of twofold self-compression of signal pulses in a beta-barium borate parametric amplifier pumped by either 40- or 80-fs pulses from a Ti:sapphire laser.

Use of mismatched grating pairs in chirped-pulse amplification systems.

We demonstrate for the first time to our knowledge the use of mismatched grating pairs between the stretching and compression systems in a chirped-pulse amplification laser. Pulses as short as 57 fs are generated with 2000-lines/mm gratings in the compressor and 1200-lines/mm gratings in the stretcher.

Generation of 18-fs, multiterawatt pulses by regenerative pulse shaping and chirped-pulse amplification.

Transform-limited, 18-fs pulses of 4.4-TW peak power are produced in a Ti:sapphire-based chirped-pulsed amplification system at a repetition rate of 50 Hz. Regenerative pulse shaping is used to control gain narrowing during amplification, and an optimized, quintic-phase-limited dispersion compensation scheme is used to control higher-order phase distortions over a bandwidth of ~100 nm. Seed pulses are temporally stretched >100,000 times before amplification.

Generation of 25-TW, 32-fs pulses at 10 Hz.

We have developed a femtosecond laser chain that generates 25-TW pulses of less than 35 fs at 10 Hz with focused intensities higher than 5 x 10(19) W/cm(2) and an average power of 8 W. This system is optimized for a broad transmission bandwidth and includes an aberration-free stretcher compressor.