Guy Mayer

Kerr effects in two-phase systems with bubbles and drops

Abstract We study the deformations induced by an electric field on small fluid spheres dispersed in a fluid medium of different dielectric constant and the birefringence which results from these deformations. Static and dynamical features of these Kerr effects are discussed.

Bremsstrahlung and photoconduction in dense gases

Abstract We report bremsstrahlung experiments in dense gases. The first conduction electrons required for these observations are obtained by a two-steps ionization process acting on dopant molecules.

Photoionization experiments in dense argon gas

Abstract At densities above 50 Amagats, light of frequency 2.818 x 10 4 cm -1 ionizes efficiently argon gas containing less than 1 part per million of impurities. For a given density we find for the number of free charges produced a square law dependence on light intensity. At constant light intensity the number of free charges produced varies approximately like the sixth power of density in the range 200–500 Amagats.

Emissions Optiques Et Electroniques De Solides Intensement Eclaires

Abstract In order to analyze the processes involved in the optical and electronic emissions induced on various targets by laser pulses, we have developed pyrometric methods having a time resolution of 10 −8 s. The initial temperature of the target is an important parameter which we control over a wide range. Our measurements suggest that many non-linear emission effects shown by various metals come from a non-metallic superficial layer and that they may not be accounted for by a simple heating effect. On tungsten and platinum, this superficial layer is easily destroyed in vacuum around 1200°C, which brings to the two photons photoelectric yield a decrease of at least three orders of magnitude.

Gamma-rays generation by fast electrons travelling through antiferroelectric or antiferromagnetic crystalline structures

Abstract With the help of the Weizsacker-Williams model we analyze the generation of gamma-rays by fast electrons travelling through some kinds of antiferroelectric or antiferromagnetic crystalline structures. The scattering efficiency of this process is calculated as a function of angle and frequency and is then compared to the normal bremsstrahlung efficiency.

A laser system for optical waves mixing experiments

Abstract We built a neodymium glass laser delivering two simultaneous pulses having a frequency separation tunable by steps from 10 to 90 cm-1. We used it to measure non-linear polarizabilities in glases and carbon disulfide by conventional coherent second Stokes and anti-Stokes techniques with unusual spectral filtering requirements. With the device described one can study in the 10-13–10-14 s range the kinetics of effects induced by the square of an electric field.

Elements optiques utilisant des gaz en vibration

Abstract We have studied the optical properties of cylindrical resonant cavities filled with gases in which radial acoustical standing waves are excited. When the oscillation mode is of the Bessel J 0 kind, the system is somewhat equivalent to a lens alternately convergent and divergent. With these optical components, it is easy to modulate light and to trigger lasers of any colour.

Laser-induced amplification and visualization of β-ray ionized tracks in dense gases

Abstract We describe some experiments on Bremsstrahlung energy transfer from an intense laser light towards electrons sorrounded by a dense gas. The electrons gain eventually enough energy to radiate light and to excite and ionize the surrounding atoms. We have measured the spectra of the light emitted in these conditions and the electron number multiplication factor resulting from successive ionization. In krypton we observe that a static field enhances significantly the rate of energy transfer from light to electrons. At the pressure of 200 bar we obtained controllable electron multiplication factors up to 106. At this level of amplification the ionized track of a 90Yβ-ray becomes visible. This latent electronic image development takes place in 10−8s.

Light induced mechanical effects connected with Fresnel coefficients of drag

Abstract Fresnel and Fizeau have shown that the refraction index of matter depends on its velocity. We discuss the eventuality of a corresponding reverse effect: a travelling wave may induce momentum changes in transparent matter.

Interaction de particules polarisables avec un reseau d'ondes presque stationnaire

Abstract In an electromagnetic field consisting of two waves (ω + ) and (ω - ) propagating in opposite directions, and having frequencies ω+ 1 2 Δω and ω- 1 2 Δω, respectively, polarizable particles are dragged along the direction of the (ω + ) wave. The stimulated scattering of ω + photons into ω - photons supplies the medium with the energy to be dissipated against viscous forces. Conversely, if the particles are forced into motion in a strictly stationary field, the ratio of the respective intensities of ω + and ω - will change. We show that these “two-photons drag” effects which are closely tied to fluctuations in scattering concentration can be used to measure the number, size and mobility of charged or neutral particles dispersed in a host medium.