Desktop cutting of paper using a single emitter laser diode and inkjet printing

International audienceLaser cutting of paper is widely used in the paper conversion industry. CO 2 lasers are well suited for this type of applications. Desktop printing is a large market both for digital photography, document management and graphics applications, but it still lacks advanced cutting and scoring ability, and CO 2 lasers seem costly to be integrated in mass-market printers. For that reason, mass-scalable and low-cost semiconductor laser diodes would be very advantageous to add paper cutting and scoring features in desktop printers. However, common paper can not be cut properly using visible or Near Infrared (NIR) laser diode since it has a very poor absorption at these wavelengths. We report here an innovative solution to achieve paper cutting or scoring using a 1 W single emitter NIR laser diode, within an inkjet printer. A special ink that absorbs the NIR light, and that penetrates all through the paper, is first disposed on the lines to be cut. Then, the laser diode goes along the lines to be cut. We show that a cutting speed of 2m/min can be achieved on 80g/m 2 conventional paper. The influence of the optical properties of the ink on the cutting speed are discussed, as well as focussing issues. In particular, we show that invisible inks are suitable, and very clear-cut edges can be obtained. The perspective of this technique are discussed

Enhancement of scattering and reflectance properties of plasma-sprayed alumina coatings by controlling the porosity

nombre de pages = 5International audienceThe plasma-spraying process generates materials with typical, porous and complex, microstructures. Inspired by Dielectric Multilayer Mirrors (DMMs), thermal sprayed media may be used in the field of optics, particularly for making scattering and reflecting coatings suitable for a large range of wavelengths. In fact, pores inside plasma sprayed matrix create numerous optical index discontinuities, similarly to the gaps created in DMMs, in order to obtain high reflectivity. The porosity of coatings microstructure can be customized by selection of plasma sprayed process parameters. This study aimed to optimize scattering and reflectance properties in porous alumina by the control of spray parameters resulting in the optimized porosity. A self-supporting bi-layer with a diffuse reflectance over 90% over a large band of wavelengths was obtained. The first layer (micro-structured), which is thick enough to support the free standing, was prepared by atmospheric plasma spraying (APS). The second layer (nanostructured) was manufactured by suspension plasma spraying (SPS) over the first layer in order to enhance the reflectance at short wavelengths

Multi-scale modeling of radiation heat transfer through nanoporous superinsulating materials

International audienceIn this contribution, we focus on the extraordinarily high level of thermal insulation produced by nanoporous materials, which can achieve thermal conductivities down to a few when they are evacuated down to a primary vacuum. Our objective here is to quantify the level of radiation heat transfer traveling through a nanoporous material in relation with its composition. Our model is based on the " non-gray anisotropically scattering Rosseland approximation " , which allows the definition of a " radiation thermal conductivity " expressed as a function of the optical properties (complex optical index spectra), mean sizes and volume fractions of the different populations of particles constituting the material. With the help of this simple model, one can draw interesting conclusions concerning the impacts of different parameters related to the microstructure of the nanoporous material on the amplitude of the radiation heat transfer. In the future, this model should help to orient the formulation of new nanoporous materials with optimized radiative properties. 1 mW.m .K − −

La théorie de MIE et l'approximation dipolaire discrète pour le calcul des propriétés radiatives des milieux particulaires Application aux matériaux nanostructurés

DoctoralDans ce document, nous nous intéressons aux milieux semi-transparents non pas homogènes mais particulaires, i. e. constitués d’une phase solide ou liquide dispersée sous forme de particules dans un milieu hôte n’absorbant pas le rayonnement ; les nuages (ensembles de gouttelettes d’eau ou de cristaux de glace en suspension dans l’air), les fumées (où cette fois ce sont de fines particules solides qui sont en suspension dans l’air), l’atmosphère (population de molécules gazeuses se comportant comme autant de particules de très faible taille) ou encore les matériaux nanostructurés constitués de nanoparticules solides agglomérées sont quelques exemples particuliers de cette famille de milieux semi-transparents hétérogènes. Nous allons voir qu’il existe des outils théoriques permettant de calculer les spectres des propriétés radiatives βλ , ωλ et Φλ (n′,n) de ces milieux ; dans ce qui suit, nous proposons le survol de deux de ces techniques basées sur la théorie de Mie d’une part et sur l’approximation dipolaire discrète d’autre part

Multi-scale Modeling of Radiation Heat Transfer through Nanoporous Superinsulating Materials

International audienceIn this contribution, the extraordinarily high level of thermal insulation produced by nanoporous materials, which can achieve thermal conductivities down to a few mW·m −1 ·K −1 when they are evacuated to a primary vacuum, is highlighted. The objective here is to quantify the level of radiation heat transfer traveling through a nanoporous material in relation with its composition. The model used here is based on the " non-gray anisotropically scattering Rosseland approximation, " which allows the definition of a " radiation thermal conductivity " expressed as a function of the optical properties (complex optical index spectra), mean sizes and volume fractions of the different populations of particles constituting the material. With the help of this simple model, one can draw interesting conclusions concerning the impacts of different parameters related to the microstructure of the nanoporous material on the amplitude of the radiation heat transfer. In the future, this model should help to orient the formulation of new nanoporous materials with optimized radiative properties

Mie Theory and the Discrete Dipole Approximation. Calculating Radiative Properties of Particulate Media, with Application to Nanostructured Materials

International audienceRadiative transfer in a semi-transparent medium can be described by a spacetime dependent directional monochromatic specific intensity field L λ (r, n,t), where λ is the wavelength, r the field point, n the unit direction vector, and t the time. This field L λ (r, n,t) obeys an integro-differential equation called the radiative transfer equation (RTE) which has the general form [1]: 1 c λ ∂ L λ (r, n,t) ∂t + n · ∇ r L λ (r, n,t) = −(κ λ + σ λ)L λ (r, n,t) + κ λ n 2 λ L 0 λ T (r,t) + σ λ 4π 4π Φ λ (n , n)L λ (r, n ,t)dΩ. (7.1) In this formulation, c λ is the speed of energy propagation in the semi-transparent medium, while ∇ r is the gradient with respect to position r, n λ is the refractive index, i.e., the real part of the complex optical index m λ of the medium, T (r,t) is the temperature field in the medium, and L 0 λ (T) is the specific intensity of the equilibrium radiation at temperature T. Finally, κ λ , σ λ , and Φ λ (n , n) are the bulk radiative properties of the medium, viz., its absorption coefficient, scattering coefficient , and scattering phase function, respectively. Introducing the extinction coefficient β λ = κ λ + σ λ and scattering albedo ω λ = σ λ /β λ , the steady-state version of the RTE (7.1) (valid on time scales such that the propagation of radiation can be assumed instantaneous) can be written in the form 1 β λ n · ∇ r L λ (r, n,t) = −L λ (r, n,t) + (1 − ω λ)

Optical characterization by temporal deconvolution of one-dimensional laser-ultrasonics signals – Part 1 : theory

International audienceThe laser thermoelastic generation of ultrasound is a promising technique with many potential applications, but it is also a complicated process with many physical phenomena involved. Contrary to a conventional piezoelectric transducer generation, which is a surface phenomenon, a laser generation can activate acoustic sources within the material by optical penetration of the excitation wavelength, resulting in asynchronous wave arrivals at a given point. More generally, in the case of a non-dispersive isotropic material, the laser-ultrasonics displacement signals result from temporal convolutions between optical penetration, laser pulse duration and laser spot extension effects. In this paper, a deconvolution technique is presented that extracts the laser pulse duration contribution from the experimental displacement signals. This deconvolution scheme applied to 1D experiments, in which the laser excitation is spread over a sufficiently large area on the front side of the sample, allows the evaluation of both the optical absorption coefficient and the longitudinal acoustic velocity of the material

Optical characterization by temporal deconvolution of one-dimensional laser-ultrasonics signals – Part 2 : experiment

International audienceIn an other contribution (also presented at the 9th ICPPP Conference), we expose the theory of a data processing technique that extracts the laser pulse duration-related convolution from 1D laser-ultrasonics signals and then allows the quantitative evaluation of both the optical absorption coefficient and the longitudinal acoustic velocity from the convolution-free signals. This paper is the continuation of that contribution, and consists in the experimental validation of the data processing technique

Optical characterization by temporal deconvolution of 1-D laser-ultrasonics signals part 2: Experiment

International audienceIn an other contribution (also presented at the 9th ICPPP Conference), we expose the theory of a data processing technique that extracts the laser pulse duration-related convolution from 1D laser-ultrasonics signals and then allows the quantitative evaluation of both the optical absorption coefficient and the longitudinal acoustic velocity from the convolution-free signals. This paper is the continuation of that contribution, and consists in the experimental validation of the data processing technique