arXiv subjects

Alain Miffre

Publications and source records attributed to Alain Miffre.

10 recordsLinked to original sources

arXiv2020

On the use of light polarization to investigate the size, shape and refractive index dependence of backscattering Angstroem exponents

In this letter, we exploit the polarization property of light to investigate the Angstroem exponent describing the wavelength dependence of optical backscatter between two wavelengths. Where previous interpretation of Angstroem exponent was that of a particles size indicator, the use of light polarization makes it possible to investigate the Angstroem exponent dependence on the particles shape by separately retrieving the backscattering Angstroem exponent of the spherical and nonspherical particles contained in an atmospheric particle mixture. As an output, analytical solutions of the Maxwell equations, Lorenz Mie theory, spheroidal model,can then be applied to investigate the Angstroem exponent dependence on the particles size and complex refractive index for each assigned shape. Interestingly, lidar retrieved vertical profiles of backscattering Angstroem exponents specific to s and ns particles can be used by the optical community to evaluate a range of involved particles sizes and complex refractive indices for both particles shapes, spherical and nonspherical, as we remotely demonstrate on a case study dedicated to a dust nucleation event.

physics.ao-ph↗

arXiv2008

Dispersion compensation in atom interferometry by a Sagnac phase

We reanalyzed our atom interferometer measurement of the electric polarizability of lithium now accounting for the Sagnac effect due to Earth rotation. The resulting correction to the polarizability is very small but the visibility as a function of the applied phase shift is now better explained. The fact that the Sagnac and polarizability phase shifts are both proportional to $v^{-1}$, where $v$ is the atom velocity, suggests that a phase shift of the Sagnac type could be used as a counterphase to compensate the electric polarizability phase shift. This exact compensation opens the way to higher accuracy measurements of atomic polarizabilities and we discuss how this can be practically done and the final limitations of the proposed technique.

quant-ph↗

arXiv2006

Test of the isotopic and velocity selectivity of a lithium atom interferometer by magnetic dephasing

A magnetic field gradient applied to an atom interferometer induces a $M$-dependent phase shift which results in a series of decays and revivals of the fringe visibility. Using our lithium atom interferometer based on Bragg laser diffraction, we have measured the fringe visibility as a function of the applied gradient. We have thus tested the isotopic selectivity of the interferometer, the velocity selective character of Bragg diffraction for different diffraction orders as well as the effect of optical pumping of the incoming atoms. All these observations are qualitatively understood but a quantitative analysis requires a complete model of the interferometer.

quant-ph↗

arXiv2006

Atom interferometry

In this paper, we present a brief overview of atom interferometry. This field of research has developed very rapidly since 1991. Atom and light wave interferometers present some similarities but there are very important differences in the tools used to manipulate these two types of waves. Moreover, the sensitivity of atomic waves and light waves to their environment is very different. Atom interferometry has already been used for a large variety of studies: measurements of atomic properties and of inertial effects (accelerations and rotations), new access to some fundamental constants, observation of quantum decoherence, etc. We review the techniques used for a coherent manipulation of atomic waves and the main applications of atom interferometers.

quant-ph↗

arXiv2006

Vibration induced phase noise in Mach-Zehnder atom interferometers

The high inertial sensitivity of atom interferometers has been used to build accelerometers and gyrometers but this sensitivity makes these interferometers very sensitive to the laboratory seismic noise. This seismic noise induces a phase noise which is large enough to reduce the fringe visibility in many cases. We develop here a model calculation of this phase noise in the case of Mach-Zehnder atom interferometers and we apply this model to our thermal lithium interferometer. We are thus able to explain the observed dependence of the fringe visibility with the diffraction order. The dynamical model developed in the present paper should be very useful to further reduce this phase noise in atom interferometers and this reduction should open the way to improved interferometers.

quant-ph↗

arXiv2005

Atom interferometry measurement of the electric polarizability of lithium

Using an atom interferometer, we have measured the static electric polarizability of $^7$Li $α=(24.33 \pm 0.16)\times10^{-30} $ m$^3$ $= 164.19\pm 1.08 $ atomic units with a 0.66% uncertainty. Our experiment, which is similar to an experiment done on sodium in 1995 by D. Pritchard and co-workers, consists in applying an electric field on one of the two interfering beams and measuring the resulting phase-shift. With respect to D. Pritchard's experiment, we have made several improvements which are described in detail in this paper: the capacitor design is such that the electric field can be calculated analytically; the phase sensitivity of our interferometer is substantially better, near 16 mrad/$\sqrt{Hz}$; finally our interferometer is species selective it so that impurities present in our atomic beam (other alkali atoms or lithium dimers) do not perturb our measurement. The extreme sensitivity of atom interferometry is well illustrated by our experiment: our measurement amounts to measuring a slight increase $Δv$ of the atom velocity $v$ when it enters the electric field region and our present sensitivity is sufficient to detect a variation $Δv/v \approx 6 \times 10^{-13}$.

quant-ph↗

arXiv2005

Measurement of the electric polarizability of lithium by atom interferometry

We have built an atom interferometer and, by applying an electric field on one of the two interfering beams, we have measured the static electric polarizability of lithium with a 0.66 % uncertainty. Our experiment is similar to an experiment done on sodium in 1995 by D. Pritchard and co-workers, with several improvements: the electric field can be calculated analytically and our phase measurements are very accurate. This experiment illustrates the extreme sensitivity of atom interferometry: when the atom enters the electric field, its velocity increases and the fractional change, equal to 4 x 10^(-9) for our largest field, is measured with a 10^(-3) accuracy.

quant-ph↗

arXiv2005

Lithium atom interferometer using laser diffraction : description and experiments

We have built and operated an atom interferometer of the Mach-Zehnder type. The atomic wave is a supersonic beam of lithium seeded in argon and the mirrors and beam-splitters for the atomic wave are based on elastic Bragg diffraction on laser standing waves at 671 nm. We give here a detailed description of our experimental setup and of the procedures used to align its components. We then present experimental signals, exhibiting atomic interference effects with a very high visibility, up to 84.5 %. We describe a series of experiments testing the sensitivity of the fringe visibility to the main alignment defects and to the magnetic field gradient.

quant-ph↗

arXiv2004

Parallel Temperatures in Supersonic Beams: Ultra Cooling of Light Atoms seeded in a Heavier Carrier Gas

We have found recently that, in a supersonic expansion of a mixture of two monoatomic gases, the parallel temperatures of the two gases can be very different. This effect is large if the seeded gas is highly diluted and if its atomic mass is considerably smaller than the one of the carrier gas. In the present paper, we present a complete derivation of our theoretical analysis of this effect. Our calculation is a natural extension of the existing theory of supersonic cooling to the case of a gas mixture, in the high dilution limit. Finally, we describe a set of temperature measurements made on a beam of lithium seeded in argon. Our experimental results are in very good agreement with the results of our calculation.

physics.atom-ph↗

arXiv2003

Diffraction phases in atom interferometers

Diffraction of atoms by laser is a very important tool for matter wave optics. Although this process is well understood, the phase shifts induced by this diffraction process are not well known. In this paper, we make analytic calculations of these phase shifts in some simple cases and we use these results to model the contrast interferometer recently built by the group of D. Pritchard at MIT. We thus show that the values of the diffraction phases are large and that they probably contribute to the phase noise observed in this experiment.

quant-ph↗