Nanosecond and femtosecond ablation of La0.6Ca0.4CoO3: a comparison between plume dynamics and composition of the films

Thin films of La0.6Ca0.4CoO3 were grown by pulsed laser ablation with nanosecond and femtosecond pulses. The films deposited with femtosecond pulses (248nm, 500fs pulse duration) exhibit a higher surface roughness and deficiency in the cobalt content compared to the films deposited with nanosecond pulses (248nm, 20ns pulse duration). The origin of these pronounced differences between the films grown by ns and fs ablation has been studied in detail by time-resolved optical emission spectroscopy and imaging. The plumes generated by nanosecond and femtosecond ablation were analyzed in vacuum and in a background pressure of 60 Pa of oxygen. The ns-induced plume in vacuum exhibits a spherical shape, while for femtosecond ablation the plume is more elongated along the expansion direction, but with similar velocities for ns and fs laser ablation. In the case of ablation in the background gas similar velocities of the plume species are observed for fs and ns laser ablation. The different film compositions are therefore not related to different kinetic energies and different distributions of various species in the plasma plume which has been identified as the origin of the deficiency of species for other material

Advances in multispectral and hyperspectral imaging for archaeology and art conservation

Multispectral imaging has been applied to the field of art conservation and art history since the early 1990s. It is attractive as a noninvasive imaging technique because it is fast and hence capable of imaging large areas of an object giving both spatial and spectral information. This paper gives an overview of the different instrumental designs, image processing techniques and various applications of multispectral and hyperspectral imaging to art conservation, art history and archaeology. Recent advances in the development of remote and versatile multispectral and hyperspectral imaging as well as techniques in pigment identification will be presented. Future prospects including combination of spectral imaging with other noninvasive imaging and analytical techniques will be discussed

Pathways control in modification of solid surfaces induced by temporarily separated femtosecond laser pulses

International audienceReaction control by laser light is a unique method of the reaction dynamics mastery in the molecular chemistry. We provide evidence of phase control processing with femtosecond lasers in macroscopic solids. Rutile TiO2 monocrystals with (001) and (100) surface orientations were irradiated with repetitive pulses of femtosecond KrF laser of variable fluences and a temporal delay between two superimposed linearly polarized beams. The appearance of three types of surface morphology was thoroughly analyzed: low-spatial frequency laser-induced periodic surface structures (LSFL), grooves and unusual featureless flat area (FFA). The interaction of light with the excited surface led to the onset or suppression of the subwavelength LSFL, depending on whether the temporal delay between laser beams is larger or smaller than the critical value of ~6 ps. By contrast, the suprawavelength grooves and FFA appeared at longer temporal delays. A strong decrease of the grooves onset energy was observed on the (001) oriented crystal after the delay of ~8 ps; the decrease of onset energy was also observed on the (100) oriented crystal, where FFA appeared instead of grooves. The critical delay is discussed in framework of a phenomenological model describing the energy evolution of excited transient states along the "reaction" coordinate

Surface modification of monocrystalline zinc oxide induced by high-density electronic excitation

International audienceThe domain formation in Fe/Ni/Fe nanoscale magnetic antidot arrays J. Appl. Phys. 111, 063902 (2012) Post-synthesis heat treatments of γ-Fe2O3 nanoparticles embedded in a refractory matrix: From annealing of structural defects to doping J. Appl. Phys. 111, 07B541 (2012) Fabrication of FePt networks by porous anodic aluminum oxide J. Appl. Phys. 111, 07B923 (2012) Invited Article: A materials investigation of a phase-change micro-valve for greenhouse gas collection and other potential applications Rev. Sci. Instrum. 83, 031301 (2012) One-step fabrication of L10 FePt nanocubes and rods by cluster beam deposition J. Appl. Phys. 111, 07B535 (2012) Additional information on J. Appl. Phys. Journal Homepage: http://jap.aip.org/ Journal Information: http://jap.aip.org/about/about_the_journal Top downloads: http://jap.aip.org/features/most_downloaded Information for Authors: http://jap.aip.org/authors Strong modifications of semiconductors can be provoked by high-density electronic excitation. We report on surface structuring of monocrystalline wurtzite O-face (0001) ZnO excited by UV femtosecond laser pulses (248 nm) below the ablation threshold. At fluences above 11 mJ/cm 2 , nanoholes of D¼10 nm diameter appear quasi-periodically separated by a distance $30 nm (¼3 D). Dual-pulse (pump-pump) experiments permit estimation of the electronic excitation lifetime responsible for this nanostructuring, which is in agreement with the electron-hole plasma lifetime 220 ps. The nanostructuring results in a smaller monocrystalline domain of$0.1 lm size and increases the crystalline interplane c-distance by 0.11%. The excitonic luminescence of the irradiated sample is found to increase by about 10 times. The nanostructuring remains stable in a limited range of laser fluences: above 40 mJ/cm 2 the surface melts, which accelerates the photoinduced bonds breaking leading to surface erosion. We tentatively ascribe the related mechanism to the nucleation-growth of cluster vacancies at crystal dislocations accelerated by the non-thermal (electronic) melting of the surface layer. At fluences lower than 11 mJ/cm 2 , larger volcano-like features of 60-nm diameter were observed. The characteristic crater shape and irregular surface repartition permit their assignment to thermal explosion of impurities due to multiple exciton condensation

Development of a methodology for the characterisation and assessment of biodeteriogens on archaeological surfaces by use of a portable LED-induced fluorescence instrument

Abstract The present study focuses on the development of a fast, non-invasive methodology, appropriate for the detection and characterization of biodeterioration present on the surface of archaeological/historical stone objects and monuments, by exploiting the characteristic fluorescence emission of biological deposits. Fluorescence spectra were collected by use of a portable LED (Light Emitting Diode)-Induced Fluorescence (LED-IF) instrument. Three limestone fragments and one mortar fragment, from different monuments in Greece, presenting various types of biodeterioration on their surface, have been investigated in the laboratory. First, fluorescence emission spectra were acquired with a benchtop laboratory spectrofluorometer in order to select the optimum excitation wavelengths for the fluorophores present in the biological crust. An evaluation of the portable LED-IF instrument was conducted by assessing the performance of its optical components and different LED excitation sources, while an investigation of several experimental parameters on the fluorescence signal was also performed. Furthermore, issues related to the efficiency of detection and identification of biological growth have been studied, such as the effect of sample surface wetting on the fluorescence signal. The results of the present study demonstrate that the LED-IF instrument can be used for a fast and reliable assessment of the presence of biodeterioration on monuments

A new compact laser source for portable applications

International audienc