Search results for "laser"
showing 10 items of 3161 documents
Lasergrammetry and high precision topography measurements to study a complex fortified building: Tour de la Pelote (Besançon, France)
2018
International audience
On the Schwarzschild Effect in 3D Two‐Photon Laser Lithography
2019
International audience; The two‐photon Schwarzschild effect in photoresists suitable for 3D laser lithography is revisited. The study ranges over seven orders of magnitude in exposure time (from 1 µs to 10 s) and investigates a wide variety of different photoresist compositions. For short exposure times (“regime I”), the laser power at the polymerization threshold can scale with the inverse square root of the exposure time, as naively to be expected for two‐photon absorption. Substantial deviations occur, however, for low photoinitiator concentrations. For intermediate exposure times (“regime II”), a Schwarzschild‐type of behavior is found, as discussed previously. For very long exposure ti…
Surface plasmon interference excited by tightly focused laser beams
2007
International audience; We show that interfering surface plasmon polaritons can be excited with a focused laser beam at normal incidence to a plane metal film. No protrusions or holes are needed in this excitation scheme. Depending on the axial position of the focus, the intensity distribution on the metal surface is either dominated by interferences between counterpropagating plasmons or by a two-lobe pattern characteristic of localized surface plasmon excitation. Our experiments can be accurately explained by use of the angular spectrum representation and provide a simple means for locally exciting standing surface plasmon polaritons.
Expansion dynamics of the plasma plume formed by the impact of a nanosecond Nd : YAG laser beam on metallic surface under atmospheric conditions : ex…
2010
Laser ablation in the air at atmospheric pressure is nowadays frequently applied in industry, chemical analysis, surgery… For a further development of laser ablation based technologies, it is necessary to better understand the laser – matter interaction. During the impact of a laser pulse on the surface of the treated material, a plasma plume forms above the target surface. This plume contains particles (electrons, ions, atoms) of ablated matter, as well as of ambient gas, if present. During the laser pulse, this plume absorbs a large amount of the laser beam energy, thus reducing the quantity of the laser radiation arriving to the target surface. Dimensions, as well as parameters of this p…
Şeffaf cisimlerim 3B taranması
2010
Many practical tasks in industry, such as automatic inspection or robot vision, often require scanning of three-dimensional shapes with non-contact techniques. However, transparent objects, such as those made of glass, still pose difficulties for classical scanning techniques. The reconstruction of surface geometry for transparent objects is complicated by the fact that light is transmitted through, refracted and in some cases reflected by the surface. Current approaches can only deal relatively well with sub-classes of objects. The algorithms are still very specific and not generally applicable. Furthermore, many techniques require considerable acquisition effort and careful calibration. T…
Residual Phase Noise Measurement of Optical Second Harmonic Generation in PPLN Waveguides
2017
We report on the characterization, including residual phase noise and fractional frequency instability, of fiber-coupled PPLN non-linear crystals. These components are devoted to frequency doubling 871 nm light from an extended-cavity diode laser to produce a 435.5 nm beam, corresponding to the ytterbium ion electric quadrupole clock transition. We measure doubling efficiencies of up to 117.5 %/W. Using a Mach-Zehnder interferometer and an original noise rejection technique, the residual phase noise of the doublers is estimated to be lower than ${\rm -35\, dBrad^2/Hz}$ at 1 Hz, making these modules compatible with up-to-date optical clocks and ultra-stable cavities. The influence of externa…
Fonctionnalisation de surfaces métalliques par des couches minces d'oxynitrures de titane obtenues par irradiation laser sous atmosphère contrôlée et…
2013
The technological advances in areas such as automotive and aerospace industries require materials capable of withstanding demanding conditions. Surface treatments are effective tools to improve the surface properties of materials while preserving their bulk properties. Besides many conventional processes, laser treatments are efficient methods for hardening and increasing the durability of materials. This work is focused on the growth of titanium oxynitride surface layers by laser irradiation of pure titanium plates with nanosecond pulsed sources. The influence of the laser treatment conditions on the composition and the structure of these surface layers was studied. In particular, for lase…
Comportement en fatigue thermomécanique à haute température d’un système barrière thermique texturé par laser
2020
In service life of Thermal Barrier Coating (TBC) systems for blade applications can be limited by the top-coat (TC) spallation under thermo-mechanical fatigue (TMF) loadings. To improve its TMF life, laser texturing at the bond-coat/top coat interface in the CMSX-4 Plus / γ-γ’ BC/ EB-PVD TC system has been investigated.Thanks to the study of the laser-matter interaction, it seems that the different Ni-based single crystal superalloys have similar laser ablation behaviors and they present almost no sub-surface damage after ablation. Nevertheless, the formation of melted matter near created cavities, possibly recrystallized, is often observed.Different patterns (holes, lines, grids) have been…
Towards automated and operational forest inventories with T-Lidar
2011
International audience; Forest inventory automation has become a major issue in forestry. The complexity of the segmentation of 3D point cloud is due to mutual occlusion between trees, other vegetation, or branches. That is why, the applications done until now are limited to the estimation of the DBH (Diameter at Breast Height), the tree height and density estimation. Furthermore other parameters could also be detected, such as volume or species of trees (Reulke and Haala) . . . This paper presents an effective approach for automatic detection, isolation of trees and DBH estimation. Tree isolation is achieved using an innovative approach based on a clustering methodology followed by a skele…
On the performance of wavelength meters : Part 1 : consequences for medium-to-high-resolution laser spectroscopy
2020
Present-day laser-spectroscopy experiments increasingly rely on modern commercial devices to monitor, stabilize, and scan the wavelength of their probe laser. Recently, new techniques are capable of achieving unprecedented levels of precision on atomic and nuclear observables, pushing these devices to their performance limits. Considering the fact that these observables themselves are deduced from the frequency difference between specific atomic resonances, in the order of MHz–GHz, the uncertainty on the output of the device measuring the wavelength is often directly related to the final systematic uncertainty on the experimental results. Owing to its importance, the performance of several …