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Light beams may carry both a spin and an orbital angular momentum (OAM). While the former is associated to their polarization state, the latter stems from the geometrical properties of their wavefront. In their prototypical form, beams with OAM have "donuts-like" intensity profile and helicoidal wavefront, carrying integral multiples of h as angular momenta. Since their "rediscovery" in the late 90's, beams with OAM of visible wavelengths have found innumerable applications in quantum optics, microscopy or information transfer. A major recent development was the generation of such beams with much smaller wavelengths — in the extreme ultraviolet (XUV) — using synchrotron sources, free electron lasers as well as high harmonic sources (HHG). In this latter case, it creates ultrashort XUV sources of beams with OAM, suited for time-resolved applications at femtosecond and attosecond time scales. Remarkably, we showed that even though HHG is a non-perturbative process, the OAM transfer from the driving beam to the harmonics was purely parametric; i.e., the q-th harmonic — which can be thought as the upconversion of q infrared photons — carries q times the OAM of the driver [3, 4]. However, this rule limits severely the flexibility in choosing the OAM of the XUV emission.

International audience; We study theoretically and experimentally high-order harmonic generation (HHG) using two noncollinear driving fields focused in gases. We show that these two fields form a nonstationary blazed active grating in the generation medium. The intensity and phase structure of this grating rule the far-field properties of the emission, such as the relative amplitude of the diffraction orders. Full macroscopic calculations and experiments support this wave-based picture of the process, complementing and extending its standard “photon” picture. This insight into the HHG process allows us to envision structuration schemes to convert femtosecond lasers to attosecond pulses with increased efficiency.

Optical vortices are currently one of the most intensively studied topics in optics. These light beams, which carry orbital angular momentum (OAM), have been successfully utilized in the visible and infrared in a wide variety of applications. Moving to shorter wavelengths may open up completely new research directions in the areas of optical physics and material characterization. Here, we report on the generation of extreme-ultraviolet optical vortices with femtosecond duration carrying a controllable amount of OAM. From a basic physics viewpoint, our results help to resolve key questions such as the conservation of angular momentum in highly nonlinear light–matter interactions, and the disentanglement and independent control of the intrinsic and extrinsic components of the photon's angular momentum at short-wavelengths. The methods developed here will allow testing some of the recently proposed concepts such as OAM-induced dichroism, magnetic switching in organic molecules and violation of dipolar selection rules in atoms., The controlled generation of extreme-ultraviolet beams with controllable topological charge has not been demonstrated. Here, Gauthier et al. report on the generation of extreme-ultraviolet optical vortices with femtosecond duration carrying a controllable amount of orbital angular momentum.

The Petawatt Aquitaine Laser (PETAL) facility was designed and constructed by the French Commissariat à l'énergie atomique et aux énergies alternatives (CEA) as an additional PW beamline to the Laser MegaJoule (LMJ) facility. PETAL energy is limited to 1 kJ at the beginning due to the damage threshold of the final optics. In this paper, we present the commissioning of the PW PETAL beamline. The first kJ shots in the amplifier section with a large spectrum front end, the alignment of the synthetic aperture compression stage and the initial demonstration of the 1.15 PW @ 850 J operations in the compression stage are detailed. Issues encountered relating to damage to optics are also addressed.

UNLABELLED: We conducted a pilot study to assess the prevalence of hypovitaminosis D among Iranian women and their newborns. Blood samples were taken from 50 mothers (age 16-40 yr) and their neonates at term delivery in the largest Tehran hospital. The results showed that 80% of the women had 25-hydroxyvitamin D (25-OHD) concentrations of less than 25 nmol/l. Mean maternal plasma calcium and phosphatase alkaline concentrations were in the normal range. The mean maternal serum immunoreactive parathyroid hormone concentration of women with hypovitaminosis D (i.e., 25-OHD levels

International audience; We present the experimental demonstration of a subaperture compression scheme achieved in the PETAL (PETawatt Aquitaine Laser) facility. We evidence that by dividing the beam into small subapertures fitting the available grating size, the sub-beam can be individually compressed below 1 ps, synchronized below 50 fs and then coherently added thanks to a segmented mirror. " Split-aperture laser pulse compressor design tolerant to alignment and line-density differences

A multi-Petawatt high-energy laser PETAL coupled to the Ligne d'Int?gration Laser (LIL) is under construction in the Aquitaine Region in France. This Petawatt laser will be dedicated to academic experiments in the fields of high energy density physics and ultra high intensity. Nd?:?glass laser chain coupled with the chirped pulse amplification (CPA technique allows delivery of high energy. Optical parametric CPA for pre-amplification and a new compression scheme will be implemented. PETAL is designed to deliver 3.6?kJ of energy in 500?fs on a target corresponding to 7.2?PW. The PETAL beam linked to the up to 60?kJ?ns UV beams from the LIL will present new scientific research opportunities.

The many advantages of broad-band systems are not fully exploitable without the availability of intense sources with high radiance and emitting on a broad spectral band. An electro-optic tuning of a commercial cw dye laser is proposed for simulating such sources. A conventional intra-cavity Pockels cell is used for simulating such sources. The main characteristics of laser emission are discussed (linewidth, polarization, tuning speed, etc.); the applications given as examples deal with metrology (surface testing) and optical transmission by spectral modulation of light.

Air Force communications has expanded from the most elementary requirements in World War I to an enormous military world-wide industry. It exceeds the requirements and capabilities of commercial systems without standardization, engineering, installation and maintenance capabilities required for the Job. A new system concept is proposed to reduce types of equipments, increase efficiency and reduce engineering, installation, operation, maintenance and supply problems.

A conventional intra-cavity Pockels cell was used to achieve tunable operation of a Rh 6G dye laser. Wavelength tuning over a broad spectral band (500 PO with driving voltages of some hundreds volts was achieved. This system is suitable for simulating broadband illumination in optical processors working with spatially coherent but temporally incoherent sources. Applications dealing with the measurement of optical path-differences through the channelled spectrum technique, surface testing by chromatic speckle phenomenon and optical transmission by spectral modulation of light are reported.© (1983) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.