Comment on Mott Scattering in strong Laser Field

The first differential cross section for Mott scattering of a Dirac-Volkov electron is reviewed. The expression (26) derived by Szymanowski et al. [Physical Review A {\bf 56}, 3846,(1997)] is corrected. In particular, we disagree with the expression of $(\frac{d\sigma}{d\Omega})$ they obtained and we give the exact coefficients multiplying the various Bessel functions appearing in the scattering differential cross section.Comment: 16 pages, LaTex, added reference for section 3, corrected some typosReport no: LPHEA 02-0

New Strong-Field QED Effects at ELI: Nonperturbative Vacuum Pair Production

Since the work of Sauter, and Heisenberg, Euler and K\"ockel, it has been understood that vacuum polarization effects in quantum electrodynamics (QED) predict remarkable new phenomena such as light-light scattering and pair production from vacuum. However, these fundamental effects are difficult to probe experimentally because they are very weak, and they are difficult to analyze theoretically because they are highly nonlinear and/or nonperturbative. The Extreme Light Infrastructure (ELI) project offers the possibility of a new window into this largely unexplored world. I review these ideas, along with some new results, explaining why quantum field theorists are so interested in this rapidly developing field of laser science. I concentrate on the theoretical tools that have been developed to analyze nonperturbative vacuum pair production.Comment: 20 pages, 9 figures; Key Lecture at the ELI Workshop and School on "Fundamental Physics with Ultra-High Fields", 29 Sept - 2 Oct. 2008, Frauenworth Monastery, Germany; v2: refs updated, English translations of reviews of Nikishov and Ritu

Modeling of humps formation during deep-penetration laser welding

A 3-D transient model based on the numerical resolution of fluid-flow and the heat transfer equations is developped for deep penetration laser welding at high welding speed regime, whic results in the humping phenomenon. The physical mechanisms included in our model concern matter melting, vaporization inducing a recoil pressure and solidification. The implementation of developed procedures called User Defined Functions working interactively with the CFD Fluent code and a dynamic mesh method allowed us to treat the problem with specific and complex boundary conditions. As a result regular humps could be observed after resolidification on the weld seam

EMITTING OF PHASE CONJUGATE ULTRASOUND WAVE INTO LIQUID BY PARAMETRICALLY EXCITED FERRITE

Phase conjugate sound waves at 6 MHz generated by polycrystalline ferrite sample at conditions of parametric magnetic field pumping over the threshold of absolute instability were studied in liquid. Conforming images of phase fronts for incident and conjugate waves were obtained. An angular anisotropy of effectivity connected with sample geometry was discovered and a method for it smoothing out is proposed. Maximum gain of acoustic wave in water was 43 dB ( 60 dB in ferrite )

Localisation of the reaction and increase in the steepness of temperature distribution in laser heating of metals

Translated from Russian (Fiz. Khim. Obrab. Mater. 1988 v. 22(3) p. 19-26)Available from British Library Document Supply Centre- DSC:9023.19(VR-Trans--4069)T / BLDSC - British Library Document Supply CentreSIGLEGBUnited Kingdo