Coherent forward stimulated-brillouin scattering of a spatially incoherent laser beam in a plasma and its effect on beam spray.

A statistical model for forward stimulated-Brillouin scattering is developed for a spatially incoherent, monochromatic, laser beam propagating in a plasma. The threshold above which the laser beam spatial incoherence cannot prevent the coherent growth of forward stimulated-Brillouin scattering is computed. It is found to be well below the threshold for self-focusing. Three-dimensional simulations confirm its existence and reveal the onset of beam spray above it. From these results, we propose a new figure of merit for the control of propagation through a plasma of a spatially incoherent laser beam.

Laser smoothing and imprint reduction with a foam layer in the multikilojoule regime.

This Letter presents first experimental results of the laser imprint reduction in fusion scale plasmas using a low-density foam layer. The experiments were conducted on the LIL facility at the energy level of 12 kJ with millimeter-size plasmas, reproducing the conditions of the initial interaction phase in the direct-drive scheme. The results include the generation of a supersonic ionization wave in the foam and the reduction of the initial laser fluctuations after propagation through 500 mum of foam with limited levels of stimulated Brillouin and Raman scattering. The smoothing mechanisms are analyzed and explained.

Strong reduction of the degree of spatial coherence of a laser beam propagating through a preformed plasma.

A strong reduction of the spatial coherence of a laser beam after its propagation through a plasma has been measured using a Fresnel biprism interferometer. The laser beam was diffraction limited; the coherence width was reduced from 40 mm in vacuum down to a few mm with the plasma. Numerical results based on a paraxial model exhibit a coherence degree close to the experimental one; they also prove the importance of taking into account the nonlocal transport effects in numerical simulations for such plasma conditions.

[Prenatal diagnosis of ovarian cysts. The ultrasonographic course and therapeutic importance]. / Diagnóstico prenatal del quiste de ovario. Evolución ecográfica y actitud terapéutica.

Before of the implantation of ultrasound there were few cases of ovarian cysts reported in literature because only the very large ones or those which result in mechanical complications produce symptoms. The authors report 17 cases of neonatal ovarian cysts diagnosed by prenatal ultrasound. All of the infants were asymptomatic after birth despite their size or being twisted. The diameter of the cysts varied from 2.5 to 10 cm. Five neonates were treated conservatively and the cysts resolved spontaneously. 12 infants underwent surgery following postnatal confirmation, 9 of these patients had complex ovarian cysts and at laparotomy all of them had torsion of the ovary, three of them were autoamputated, and 3 uncomplicated cysts because their large size or their association to a nephroblastoma. Simple cysts of the ovary tend to resolve spontaneously and therefore, must be treated conservatively. Complex cysts or simple ones larger than 4 cm that do not disappear should undergo surgical removal.