The kinetic modeling of low-pressure ($p\sim 1{-}10$ torr) stationary nitrogen discharges and the corresponding afterglows is reviewed. It is shown that a good description of the overall behavior of nitrogen plasmas requires a deep understanding of the coupling between different kinetics. The central role is played by ground-state vibrationally excited molecules, N2$(X\ ^1\Sigma_g^+,v)$, which have a strong influence on the shape of the electron energy distribution function, on the creation and destruction of electronically excited states, on the gas heating, dissociation and on afterglow emissions. N2$(X\ ^1\Sigma_g^+,v)$ molecules are actually the hinge ensuring a strong link between the various kinetics. The noticeable task done by electronically excited metastable molecules, in particular N2$(A\ ^3\Sigma_u^+)$ and N2$(a^\prime\ ^1\Sigma_u^-)$, is also pointed out. Besides contributing to the same phenomena as vibrationally excited molecules, these electronic metastable states play also a categorical role in ionization. Furthermore, vibrationally excited molecules in high v levels are in the origin of the peaks observed in the flowing afterglow for the concentrations of several species, such as N2$(A\ ^3\Sigma_g^+)$, N2$(B\ ^3\Pi_g)$, N2+$(B\ ^2\Sigma_u^+)$ and electrons, which occur downstream from the discharge after a dark zone as a consequence of the V-V pumping-up mechanism.

We present the modelling of twisted electromagnetic waveguides using helicoid coordinates. This amounts to introducing equivalent inhomogeneous anisotropic materials which are however taken into account easily by the finite element method. An interesting property of such helicoid coordinates is to preserve the intrinsically two-dimensional nature of the problem.

We report on the deposition of thin titanium carbide films on 60 mm and 100 mm Si wafers by KrF laser ablation of titanium targets in low-pressure (0.1 Pa) CH4 and C2H2 atmospheres, and on their characterization. The targets were titanium foils (purity 99.6%). Si (111) wafers, 60 and 100 mm in diameter, were used as substrates. Film characteristics (thickness, composition and crystalline structure) were studied as a function of the carbon-containing gas (C2H2 or CH4), laser fluence (4 or 6 J/cm2), substrate temperature (20 or 250 °C) and target-to-substrate distance (70–120 mm). Continuous, well adhesive polycrystalline TiC films were deposited even without any heating of the substrate. Films deposited in C2H2 ambient atmosphere are better crystallized and less prone to surface oxidation with respect to films deposited in CH4 atmosphere, in otherwise identical conditions.

This paper deals with the study of very low incident energy (0–12 eV) electron beam interactions with porous silicon (PS) substrates. It mainly concerns electron stimulated desorption (ESD) of negative H− ions ejected during a resonant bond breaking process. The experiments performed with a specific experimental set-up show that initially the PS surface was repulsive with regards to the low energy electron beam so that a reference voltage v0 = 2.44 V sets the origin of incident electron energy. Thus the resonant desorption process was centred at 7.5 eV with a threshold at 4.6 eV, close to characterisations on the hydrogenated surfaces of silicon crystals. However, the desorption yield was here very low in comparison. It was assumed that a large fraction of the incident electron beam entered the substrate depth enough without triggering significant ion desorption. Progressive shifts in the reference potentials up v0 = 5 V and significant reductions in desorption yield were caused by repeated electron bombardments with energies never exceeding 12 eV. These variations were attributed to changes in the surface composition of the porous silicon. It is assumed that residual fluorine atoms left after PS preparation might migrate towards the porous silicon surface as F− ions to enhance the electron beam repulsion. Following a general discussion, several experiments are suggested in order better to control modification of surface composition responsible for the ageing of the PS substrates.

Non-uniformity of temperatures appears as a general rule in hot nanofiber synthesis reactors, where local variations of the balance between long-range radiative heat exchanges and short-range conductive heat exchanges are driven by size and composition of structures. Metal particles larger than a few tens of nanometer are radiation captors, when fiber bodies thinner than 10 nm are transparent. We note that typical gradient lengths correspond remarkably well to usual length of nanotubes (micron range), and increase with fiber radius. For anisotropically radiating reactors as well as for furnace-type reactors, difference between radiative and conductive environments allows temperature intervals as high as several hundred degrees. Practically, axial thermal gradients arise by fiber attachment to a metallic particle, eventually at each tip (ideally with different sizes or compositions), or by attachment to a hot wall (electrode, supporting substrate, or target). The resulting thermal gradients are unusually stiff, typically 10 K µm−1. We show that local temperature evolution in early stage of nucleation is triggered by dimension of attached particle(s). We show that a diffusion flux of adatoms induced by the axial thermal gradient is quantitatively consistent with a feeding flux, as measured for different reactors. In addition, we notice that the spontaneous minimization of free energy at fiber tip is such that a temperature drop favors axial extension.

The spatial shaping of light beams is the process of redistributing the irradiance of a light beam. A correct beam shaping is essential to optimize a large number of laser-material processing applications and laser-material interaction studies. In this paper, after introducing the basic equations of the classical beam integration method to reshape and homogenize laser beams, we detail the design elements, the experimental performance and the main parameters of a novel transfocal homogenizer that is able to homogenize and reshape any light beam. Then we discuss the reliability of existing international standard parameters to evaluate the “goodness” of nearly flat-top shaped laser beams. Finally, we present examples of successful applications of this new homogenizer technology to ultraviolet irradiation experiments.

The effects of CO2 molecules upon an argon thermal plasma at atmospheric pressure are studied by optical emission spectroscopy. The excitation temperature, heavy particles temperature and electron density are measured as a function of Ar-CO2 mixture composition and discharge current. The excitation temperature is ranging from 7000 K to 12000 K, electron density from 3 × 1021 m−3 to 5.6 × 1022 m−3 and heavy particles temperature of the peripherical region of the column from 6000 K to 7000 K. Excitation temperature and electron density gradients are evaluated. The influence of the arc confinement is studied and departure from local thermal equilibrium is also discussed.

This paper investigates the dielectric properties of various air/SF6 gas mixtures based upon a cylindrical spacer model with adhering particle on the surface under homogeneous field conditions. The investigation involves a comparison with pure SF6. The flashover field strength for clean and particle contaminated spacer surface under lightning impulse (LI) and alternating voltage (AC) stress is determined. The results of the investigations show the sensitivity of air/SF6 gas mixtures to conducting particles on spacer surfaces for gas pressure up to 1000 kPa. Moreover, the correspondence between pure SF6 and air/SF6 gas mixtures for AC and LI flashover field strength range from 50 to 178 kV/cm is determined. Conclusions are drawn about the ability of air/SF6 gas mixtures to serve as technically efficient media for long Gas Insulated Transmission Lines (GITL). The results shed light on the issue of the SF6 reduction and the particle detectability in GITL.

We modify the Sedov theory to describe plasma shock waves generated in a pulsed laser ablating process. Under reasonable asymptotic behavior and boundary conditions, the propagating rules in global free space (including near areas and mid-far areas) of pulsed-laser-induced shock waves are established for the first time. In particular, the temporal behavior of energy causing a difference in the propagation characteristics between the practical plasma shock wave and the ideal shock wave in a point explosion model is detailedly discussed. The theoretical results calculated with our model are in good agreement with the corresponding experimental data. In addition, some important free parameters which could not directly be obtained from other previous works are determined naturally on the basis of our model.

Two methodologies are presented allowing to find the current density on a revolution surface to obtain a given 3D magnetic field distribution. The combination of the Biot-Savart law and the superposition theory is used to establish an algebraic relationship between the predefined magnetic field and the searched current density. Basically, two approaches are used: the continuous approach, in which the current density is modeled by an analytical function and the discrete method where the searched current density is given by a list of values that match a mesh of the magnet support. Furthermore, the use of the spherical harmonic development of the predefined magnetic field leads to a compact formulation of the inverse problem. The proposed matrix methodology has been developed for any magnet having a revolution axis (revolution magnets). A computer code which uses both approaches has been developed and gives good simulation results, which show an interesting prospects for new magnet design.

High-velocity convective and radiative drying of an optical fibre coated with an aqueous polymeric suspension is considered. This study is divided into two parts: drying is first experimentally tested using a semi-industrial device, then a heat and mass transfer model between the fibre and its environment is proposed and discretised. The comparison of experimental and numerical results consolidates the assumptions of the present model and thus allows to consider it in future to dimension an industrial coating-drying process.

In-situ spectroscopic ellipsometry is known to be very sensitive, non-invasive technique for monitoring and control of thin film growth. In the production of optical interference coatings the refractive index of the material is usually assumed to remain constant within a single layer. Under such assumption only the optical thickness of the layer can be efficiently controlled. For modern complex structures, however, even insignificant deviation from the design, due to the shift in the refractive index, can be very detrimental to the resulting performance of the coating. Simultaneous real-time determination of refractive index and growth rate is necessary in order to comply with strict specifications. If the index departs from the target value, one has to adjust process parameters and, ultimately, perform re-calculation of the filter structure to compensate for an error. We will review the work performed in our laboratory during last few years. Development of several different control strategies will be discussed and their application to the control of PECVD of optical interference coatings demonstrated. Latest work is concerned with the advances in the closed-loop control of the fabrication of optical thin films by in-situ multi-wavelength phase-modulated kinetic ellipsometry using both, direct numerical inversion algorithm for the real-time reconstruction of refractive index and layer thickness and real-time least-squire fitting-based approach. These techniques have been tested on quarter-wave index optical filters as well as on inhomogeneous refractive index profiles and demonstrated efficiency and robustness.

A series impedance method [Mason and Fair, Proc. IRE, 464 (1942); IEEE Standard on Piezoelectricity ANSI/IEEE Std 176-1987 (New York: The Institute of Electrical and Electronics Engeneers, 1987)] is the most popular way for investigation of piezoelectric properties of crystals. The AC voltage generated by a vibrating crystal achieves its maximum if a frequency of an exciting signal applied to the sample is equal to a resonance frequency of the sample. In this article a very simple experimental setup for piezoelectric measurements was described. Usually measurements of resonance frequencies are made at a constant temperature, which makes an experiment long-lasting. The experimental setup described below allows performance of the experiment in slow-change temperature regime.

We have developed an analytic solution to heat equation in vicinity of steel sample surface, heated by pulsed Gaussian laser beam, taking into account both heat transfer conduction and radiation. Then we performed a new calculation method to build up isothermal generative lines in vicinity of targeted surface. We tried to explain line distortion through comparison with some of our further studies that considered basically conduction phenomenon and that paradoxically performed non-Gaussian temperature experimental profiles.

Pulsed photoacoustic spectroscopy provides information about optical, thermal and geometrical characteristics of opaque materials. The aim of this paper is the analysis of the applicability of the finite differences method to simulate the process by which pulsed photoacoustic signal is generated by a pulsed heat source, both in time and frequency domains. The present study is extended to a two-layers absorbing system. This method is free of the limitations imposed by special cases when the analytical methods are used to resolve heat diffusion equations. This approach is analyzed through the temperature and pressure variations in the photoacoustic cell.