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Fast electron generation and propagation were studied in the interaction of a green laser with solids. The experiment, carried out with the LULI TW laser (350 fs, 15 J), used K(alpha) emission from buried fluorescent layers to measure electron transport. Results for conductors (Al) and insulators (plastic) are compared with simulations: in plastic, inhibition in the propagation of fast electrons is observed, due to electric fields which become the dominant factor in electron transport.
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We report measurements of x-ray scattering cross sections for dense plasmas created by subjecting aluminum foils to strong laser-driven shocks. A narrow cone of quasimonochromatic x-rays at approximately 4.75 keV was used to probe the shocked part of the foil and scattered photons were detected with a CCD camera. The scattering cross section shows a clear peak, indicating diffraction from the plasma. Analysis and simulation of the data suggest that radiative heating and electron-ion energy exchange are important factors in the plasma production.
RESUMO
We analyze recent experimental results on the increase of fast electron penetration in shock compressed plastic [Phys. Rev. Lett. 81, 1003 (1998)]. It is explained by a combination of stopping power and electric field effects, which appear to be important even at laser intensities as low as 10(16) W cm-2. An important conclusion is that fast electron induced heating must be taken into account, changing the properties of the material in which the fast electrons propagate. In insulators this leads to a rapid insulator to conductor phase transition.
RESUMO
The authors emphasize the importance of the relations between strabismus and amblyopia. Strabismus is often the symptom which leads to the discovery of amblyopia. Amblyopia may cause strabismus, as in organic amblyopias induced by congenital lesions of the retina or visual pathways, and visual deprivation amblyopias due to corneal opacities and/or congenital cataracts. Unilateral clouding of normally transparent media (cornea, lens, vitreum) prevents normal stimulation of the retina which is necessary to the development of binocular vision. Anisometropic amblyopias also belong to this category. More often, amblyopia is the consequence of strabismus: it is then termed "functional strabismic amblyopia". Loss of the parallelism of the two visual axes disrupts the functional balance between the images received from the two eyes. The two images are different; one is suppressed. This suppression may eventually lead to amblyopia. Amblyopia was discovered in 593 of 1 757 studied cases of strabismus. Amblyopia was the cause of strabismus in 87 patients and was functional in the remaining 506. Among these latter, visual acuity was inferior or equal to 1/10 in 241 cases and between 2/10 and 7/10 in 265. 147 children in the first group and 136 in the second could be treated. Among these patients, who were treated before the age of seven, complete recovery was obtained in approximately 1/2 of cases and improvement in more than 1/4 of first group patients and 1/3 of second group patients. Results were all the better that treatment was initiated earlier and that patients were younger.(ABSTRACT TRUNCATED AT 250 WORDS)