Jean-Marie Gagne

Study of the aerodynamic trap for containerless laser materials processing in microgravity

In the context of containerless laser processing of glasses in microgravity, a systematic study of the aerodynamic trap (ADT) has been done on the ground at both ambient and very high temperatures (≳2000 K). This work yielded a better understanding of the ADT and helped in improving its design. Experiments indicate that restoring force and sample stability depend upon the diffuser’s interior angle, flow rate, and ratio of sample to diffuser’s throat diameters. It was found that the trap’s potential energy curve versus position had a barrier height that increased with flow rate but decreased with increasing angle of the diffuser. Small angle diffusers show a greater spatial extent of the potential well, higher sphere‐to‐wall distances, and greater sample stability than larger angle diffusers. Low flow rates give quieter environments (smaller oscillations and perturbations due to the gas flow) than higher flow rates even though they are sufficient to trap the sample and damp external perturbations. Heat los...

Mechanistic study of the optogalvanic effect in a hollow-cathode discharge

Simultaneous detection of the optogalvanic effect and of the laser-induced intensity variations in emission lines in a uranium hollow-cathode discharge show that a part of the absorbed laser energy is transferred to all the species in the lamp by means of electron collisions. This transfer results in a global heating of the plasma and in an increase of ion and atom densities. From the measured nonisotopic selectivity of ion production associated with the optogalvanic effect, we conclude that impedance changes in the discharge are essentially due to the heating of the plasma. It follows that the optogalvanic effect is not a suitable scheme for isotopic enrichment by cataphoresis.

Méthode d'echantillonage des fonctions déterministes en spectroscopie: application à un spectromètre multicanal par comptage photonique. Erratum.

The sampling theorem for deterministic functions is used to locate the center of gravity of a spectral line obtained by photon counting with a multichannel spectrometer. The sampling step and the width of the channels have been evaluated to locate the line with maximum accuracy. Our analysis and experimental results give the requirements needed of a photon counting multichannel Fabry-Perot spectrometer to improve the accuracy of measurement of the spectral interval between two lines.

Thermal contact probing by photoacoustic effect

The influence on the photoacoustic signal of the thermal contact resistance at the interface sample substrate is investigated using a thin metallic foil (thickness ∼12.5 μm) as sample. The foil is either applied by pressure against the substrate or epoxyed on it. The resistance is determined by interpreting magnitude and phase data obtained by varying the laser source modulation frequency. In the light of the results obtained with the thin foil, we discuss the limitations introduced by thermal contact in the photoacoustic detection of aerosols collected on a surface.

Méthode d’echantillonnage des fonctionsdéterministes en spectroscopie: application à unspectromètre multicanal par comptage photonique

The sampling theorem for deterministic functions is used to locate the center of gravity of a spectral line obtained by photon counting with a multichannel spectrometer. The sampling step and the width of the channels have been evaluated to locate the line with maximum accuracy. Our analysis and experimental results give the requirements needed of a photon counting multichannel Fabry-Perot spectrometer to improve the accuracy of measurement of the spectral interval between two lines.

Générateur de vapeur d'uranium: la lampe à cathode creuse pulsée.

The production of uranium vapors has been studied in the (5)L(0)(6)ground state using a pulsed hollow cathode lamp. The evolution of the (238)U ((5)L(0)(6)) concentration with time has been studied with Xe and Ar as buffer gases. A density of 2.7 x 10(13) atoms cm(-3) was obtained with Xe as a buffer gas. In addition, those measurements, obtained from the absorption of a laser beam tuned to the 5758.143 A ((5)L(0)(6)-17,361(7)L(6)) transition, allowed the determination of the transition probability A = 2.1 x 10(5) sec(-1) and of the branching ratio BR = 0.08 for this transition.

Isotope shifts in 91Zr from optogalvanic saturation spectroscopy

Abstract We present experimental values of the 90Zr-91Zr isotope shift for seven lines in the spectral range of the Rhodamine 6G obtained with POLINEX and Intermodulated Saturation Optogalvanic spectroscopic techniques. The accuracy of our results, better than 20%, is indeed very good considering the small isotope shifts involved (of the order of 100 MHz). These results indicate that the addition of one neutron outside the closed, N=50, core of 90Zr results in line shifts which are consistent with the presence of an odd-even staggering effect.

Refractometer Associated with the Fabry-Perot Spectrometer

This paper describes the principles, realization, and characteristics of a refractometer used as a reference for measuring the scanning of a high resolution, photoelectric Fabry-Perot spectrometer. The precision of the measurements on this refractometer is approximately one order of magnitude greater than that obtainable with other instruments.

Mesures des deplacements isotopiques du ZrI des transitions dans le domaine de la rhodamine 6G

Abstract We present isotope shift measurements of twenty-five zirconium lines in the frequency range of the Rhodamine 6G. These measurements were obtained using Doppler-free intermodulated spectroscopy and optogalvanic detection for a zirconium vapour produced in a hollow cathode generator. A linewidth of about 20 MHz is observed. The results are tabulated as values of the isotopic shift between pairs of isotopes. The accuracy of the measurements is better than 10 MHz for most lines. Finally we compare our results with those obtained by Dontsov. We notice that Dontsovs results appear, in general, to be higher than ours. The same discrepancy is observed when comparing Dontsovs results with those from Heilig, Schmitz and Steudel for some lines of the Rh 6G frequency range.

Determination of self-absorption in emission lines from some optically thick plasmas

We present a relatively simple method by which the amount of self-absorption in laboratory-produced plasmas can be evaluated. As an illustration we apply it here to the evaluation of self-absorption in a U i resonance transition from a hollow-cathode-generated plasma. The method can be generalized to include more-complex situations.