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

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.Comment: v3 11/03/0

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

Remote Sensing Observation of New Particle Formation Events with a (UV, VIS) Polarization Lidar

Observations of new particle formation events in free troposphere are rather seldom and limited in time and space, mainly due to the complexity and the cost of the required on-board instrumentation for airplane field campaigns. In this paper, a calibrated (UV, VIS) polarization elastic lidar (2β + 2δ) is used to remotely sense new particle formation events in the free troposphere in the presence of mineral dust particles. Using very efficient (UV, VIS) light polarization discriminators (1:107) and after robust calibration, the contribution of mineral dust particles to the co-polarized (UV, VIS) lidar channels could be removed, to reveal the backscattering coefficient of the newly nucleated particles after these numerous particles have grown to a size detectable with our lidar. Since our polarization and wavelength cross-talks are fully negligible, the observed variation in the (UV, VIS) particle backscattering time–altitude maps could be related to variations in the particle microphysics. Hence, day and nighttime differences, at low and high dust loadings, were observed in agreement with the observed nucleation process promoted by mineral dust. While light backscattering is more sensitive to small-sized particles at the UV lidar wavelength of 355 nm, such new particle formation events are here for the first time also remotely sensed at the VIS lidar wavelength of 532 nm at which most polarization lidars operate. Moreover, by addressing the (UV, VIS) backscattering Angstrom exponent, we could discuss the particles’ sizes addressed with our (UV, VIS) polarization lidar. As nucleation concerns the lowest modes of the particles’ size distribution, such a methodology may then be applied to reveal the lowest particle sizes that a (UV, VIS) polarization lidar can address, thus improving our understanding of the vertical and temporal extent of nucleation in free troposphere, where measurements are rather seldom

Expériences d'interférométrie atomique avec le lithium. Mesure de précision de la polarisabilité électrique

Président du Jury : M. J.A. BESWICK, Professeur de l'Université Rapporteur : M. C. SALOMON, Directeur de Recherches, L.K.B., Paris Rapporteur : M. R. KAISER, Directeur de Recherches, I.N.L.N., Nice Examinateur : M. P. VERKERK, Directeur de Recherches, Ph.L.A.M., Lille Examinateur : M. M. BÜCHNER, Chargé de Recherches, L.C.A.R., Toulouse Directeur de thèse : M. J. VIGUE, Directeur de Recherches, L.C.A.R., Toulouse.This work presents an absolute measurement of the lithium atom electric polarizability using atom interferometry. Our result reduces by a factor of three the uncertainty on this physical quantity. After a detailed study of the lithium atom source, this work describes the construction of the Mach – Zehnder atom interferometer, based on elastic diffraction of the atomic wave by three laser standing waves almost resonant with the first resonance transition of lithium atom. The quality of our interference signals (up to 84.5 % fringe visibility) is then used to do very accurate phase measurements. On top of Zeeman effect, this work studies the influence of an electric field applied on one of the two interfering arms, separated by only 90 micrometers, to achieve a lithium atom polarizability measurement by Lo Surdo – Stark effect.Cette thèse propose une mesure absolue de la polarisabilité de l'atome de lithium par interférométrie atomique. Le résultat obtenu améliore la connaissance de cette grandeur d'un facteur trois par rapport aux mesures antérieures déjà existantes. Après une étude détaillée de la source d'atomes de lithium, ce travail s'intéresse au réglage de l'interféromètre atomique de Mach – Zehnder, qui fonctionne par diffraction élastique de l'onde atomique par trois ondes stationnaires laser, quasi résonantes avec la première transition de résonance du lithium. La qualité des signaux d'interférence observés (jusqu'à 84,5 % de visibilité) est mise à profit pour effectuer des mesures de phase d'une grande précision. Outre l'effet Zeeman, ce travail étudie l'effet d'un champ électrique appliqué sur un seul des deux chemins atomiques, distants de seulement 90 micromètres, pour mesurer la polarisabilité électrique du lithium par effet Lo Surdo – Stark

Interférométrie atomique avec l'atome de lithium (mesure de précision de la polarisabilité électrique)

TOULOUSE3-BU Sciences (315552104) / SudocSudocFranceF

Laboratory Evaluation of the (355, 532) nm Particle Depolarization Ratio of Pure Pollen at 180.0° Lidar Backscattering Angle

While pollen is expected to impact public human health and the Earth’s climate more and more in the coming decades, lidar remote sensing of pollen has become an important developing research field. To differentiate among the pollen taxa, a polarization lidar is an interesting tool since pollen exhibit non-spherical complex shapes. A key attribute is thus the lidar particle depolarization ratio (PDR) of pollen, which is however difficult to quantify as pollen are large and complex-shaped particles, far beyond the reach of light scattering numerical simulations. In this paper, a laboratory π-polarimeter is used to accurately evaluate the PDR of pure pollen, for the first time at the lidar exact backscattering angle of 180.0°. We hence reveal the lidar PDR of pure ragweed, ash, birch, pine, cypress and spruce pollens at 355 and 532 nm lidar wavelengths, as presented at the ELC 2021 conference. A striking result is the spectral dependence of the lidar PDR, highlighting the importance of dual-wavelength (or more) polarization lidars to identify pollen taxa. These spectral and polarimetric fingerprints of pure pollen, as they are accurate, can be used by the lidar community to invert multi-wavelength lidar polarization measurements involving pollen

Laboratory Evaluation of the (355, 532) nm Particle Depolarization Ratio of Pure Pollen at 180.0° Lidar Backscattering Angle

While pollen is expected to impact public human health and the Earth’s climate more and more in the coming decades, lidar remote sensing of pollen has become an important developing research field. To differentiate among the pollen taxa, a polarization lidar is an interesting tool since pollen exhibit non-spherical complex shapes. A key attribute is thus the lidar particle depolarization ratio (PDR) of pollen, which is however difficult to quantify as pollen are large and complex-shaped particles, far beyond the reach of light scattering numerical simulations. In this paper, a laboratory π-polarimeter is used to accurately evaluate the PDR of pure pollen, for the first time at the lidar exact backscattering angle of 180.0°. We hence reveal the lidar PDR of pure ragweed, ash, birch, pine, cypress and spruce pollens at 355 and 532 nm lidar wavelengths, as presented at the ELC 2021 conference. A striking result is the spectral dependence of the lidar PDR, highlighting the importance of dual-wavelength (or more) polarization lidars to identify pollen taxa. These spectral and polarimetric fingerprints of pure pollen, as they are accurate, can be used by the lidar community to invert multi-wavelength lidar polarization measurements involving pollen

Laboratory evaluation of the scattering matrix elements of mineral dust particles from 176.0 degrees up to 180.0 degrees-exact backscattering angle

International audienceIn this paper, the scattering matrix elements of an ensemble of mineral dust particles are for the first time evaluated in laboratory for scattering angles ranging from 176.0° to the π-backscattering angle of 180.0° with a high angular resolution of 0.4° and compared with the outputs of T-matrix numerical code. Elastic light scattering is addressed at near and exact backscattering angles with a newly-built laboratory polarimeter, validated on spherical particles following the Lorenz–Mie theory. The ratios fij(θ) = Fij(θ)/F11(θ) of the scattering matrix elements of mineral dust particles are then precisely evaluated in laboratory from 176.0° up to 180.0° with a 0.4° angular resolution (even 0.2° between 179.2° and 180.0°), which is new. When approaching the π-backscattering angle, the slopes of the scattering matrix elements are almost zero, as theoretically predicted by Hovenier and Guirado [17]. Moreover, our laboratory findings are found in good agreement with the outputs of the T-matrix numerical code, showing the ability of the spheroidal model to describe light-scattering by mineral dust also from near to exact backscattering. Atmospheric implications for polarization lidar retrievals are then discussed in terms of linear and circular depolarization ratios for mineral dust. These results, which complement other existing light scattering experiments, may be used to extrapolate light scattering by mineral dust particles up the π-backscattering angle, which is useful in radiative transfer and climatology, in which backscattering is involved