Electron-lattice kinetics of metals heated by ultrashort laser pulses

We propose a kinetic model of transient nonequilibrium phenomena in metals exposed to ultrashort laser pulses when heated electrons affect the lattice through direct electron-phonon interaction. This model describes the destruction of a metal under intense laser pumping. We derive the system of equations for the metal, which consists of hot electrons and a cold lattice. Hot electrons are described with the help of the Boltzmann equation and equation of thermoconductivity. We use the equations of motion for lattice displacements with the electron force included. The lattice deformation is estimated immediately after the laser pulse up to the time of electron temperature relaxation. An estimate shows that the ablation regime can be achieved.Comment: 7 pages; Revtex. to appear in JETP 88, #1 (1999

A review of the use of terrestrial laser scanning application for change detection and deformation monitoring of structures

Change detection and deformation monitoring is an active area of research within the field of engineering surveying as well as overlapping areas such as structural and civil engineering. The application of Terrestrial Laser Scanning (TLS) techniques for change detection and deformation monitoring of concrete structures has increased over the years as illustrated in the past studies. This paper presents a review of literature on TLS application in the monitoring of structures and discusses registration and georeferencing of TLS point cloud data as a critical issue in the process chain of accurate deformation analysis. Past TLS research work has shown some trends in addressing issues such as accurate registration and georeferencing of the scans and the need of a stable reference frame, TLS error modelling and reduction, point cloud processing techniques for deformation analysis, scanner calibration issues and assessing the potential of TLS in detecting sub-centimetre and millimetre deformations. However, several issues are still open to investigation as far as TLS is concerned in change detection and deformation monitoring studies such as rigorous and efficient workflow methodology of point cloud processing for change detection and deformation analysis, incorporation of measurement geometry in deformation measurements of high-rise structures, design of data acquisition and quality assessment for precise measurements and modelling the environmental effects on the performance of laser scanning. Even though some studies have attempted to address these issues, some gaps exist as information is still limited. Some methods reviewed in the case studies have been applied in landslide monitoring and they seem promising to be applied in engineering surveying to monitor structures. Hence the proposal of a three-stage process model for deformation analysis is presented. Furthermore, with technological advancements new TLS instruments with better accuracy are being developed necessitating more research for precise measurements in the monitoring of structures

EXCIMER LASERS

A review of excimer laser systems is presented, including basic physical data, technology, performances and applications. The last few years have seen a rapid development of this new type of gas lasers and of many commercial systems producing efficient high power pulses of ultra-violet radiation. After a short recall of physical principles, we give a description of the internal structure of nanosecond and picosecond excimer lasers, followed by the analysis of principal beam characteristics : output power, efficiency, pulse stability, beam profile and lifetime. Some cost considerations are also examined. The presentation of principal applications in various domains as photochemistry, material processing, non linear processes and medecine, shows how these lasers are definitely an useful tool

Les lasers moléculaires ultraviolets à excitation électronique transverse

The more recent developments of ultraviolet molecular laser, with transverse electronic pumping, are presented here. It is show that two models of electronic transitions : bound-bound and bound-unbound transitions, are in the beginning of the most part of intense ultraviolet laser lines. The second model offer some possibilities of stimulated emission which are not all worked. We point out, in the last part of this paper, some molecules from which laser lines should be possible. So, we analyze the state of the laser technology development. This has lead to realize several systems from which it is possible to have numerous laser lines with just changing the gases. As a practical consequence, may applications exist.Les plus récents développements des lasers moléculaires ultraviolets, à excitation électronique transverse sont présentés et analysés. Ces lasers peuvent être regroupés en deux familles caractérisées par le type de transition à partir de laquelle a lieu l'émission stimulée : transitions entre deux états liés et transitions entre un état supérieur lié et un état inférieur répulsif. Le second type offre des possibilités et laisse prévoir des performances supérieures à celles du premier, mais celles-ci ne sont pas encore toutes exploitées. Est également présenté l'état actuel de la technologie de ces lasers. Son développement permet de disposer de montages bien adaptés à un certain nombre d'applications. Un autre avantage est constitué par la possibilité de disposer de plusieurs raies lasers par simple changement du milieu gazeux excité. Enfin, les rendements d'émission élevés obtenus dans plusieurs cas expliquent l'intérêt porté sur les deux plans : théorique et expérimental

FACETS : A CLOUDCOMPARE PLUGIN TO EXTRACT GEOLOGICAL PLANES FROM UNSTRUCTURED 3D POINT CLOUDS

Geological planar facets (stratification, fault, joint…) are key features to unravel the tectonic history of rock outcrop or appreciate the stability of a hazardous rock cliff. Measuring their spatial attitude (dip and strike) is generally performed by hand with a compass/clinometer, which is time consuming, requires some degree of censoring (i.e. refusing to measure some features judged unimportant at the time), is not always possible for fractures higher up on the outcrop and is somewhat hazardous. 3D virtual geological outcrop hold the potential to alleviate these issues. Efficiently segmenting massive 3D point clouds into individual planar facets, inside a convenient software environment was lacking. FACETS is a dedicated plugin within CloudCompare v2.6.2 (http://cloudcompare.org/ ) implemented to perform planar facet extraction, calculate their dip and dip direction (i.e. azimuth of steepest decent) and report the extracted data in interactive stereograms. Two algorithms perform the segmentation: Kd-Tree and Fast Marching. Both divide the point cloud into sub-cells, then compute elementary planar objects and aggregate them progressively according to a planeity threshold into polygons. The boundaries of the polygons are adjusted around segmented points with a tension parameter, and the facet polygons can be exported as 3D polygon shapefiles towards third party GIS software or simply as ASCII comma separated files. One of the great features of FACETS is the capability to explore planar objects but also 3D points with normals with the stereogram tool. Poles can be readily displayed, queried and manually segmented interactively. The plugin blends seamlessly into CloudCompare to leverage all its other 3D point cloud manipulation features. A demonstration of the tool is presented to illustrate these different features. While designed for geological applications, FACETS could be more widely applied to any planar objects