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arXiv:1002.2616 · Physical Review A

Fast nondestructive temperature measurement of two-electron atoms in a magneto-optical trap

Matteo Cristiani, T. Valenzuela, Hannes Gothe, Jürgen Eschner

Published Jun 17, 2010• 12 citations

Abstract

We extend the technique originally proposed by [Honda et al., Phys. Rev. A 59, R934 (1999)] to measure the temperature of ytterbium and alkaline-earth-metal atoms confined in a magneto-optical trap (MOT). The method is based on the analysis of excitation spectra obtained by probing the ${}^{1}{\text{S}}_{0}\ensuremath{\rightarrow}{}^{3}{\text{P}}_{1}$ intercombination line. Thanks to a careful analysis and modeling of the effects caused by the MOT light on the probe transition we overcome the resolution and precision limits encountered in previous works. Ground-state light shift and Rabi broadening are measured and successfully compared with calculated values. This knowledge allows us to properly extract the Doppler contribution to the linewidth, thus obtaining a reliable measurement of the cloud temperature. We finally show how spectroscopy on free-falling atoms provides an alternative method to determine the sample temperature which resembles the standard time-of-flight technique.

DOI: 10.1103/physreva.81.063416

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We extend the technique originally proposed by [Honda et al., Phys. Rev. A 59, R934 (1999)] to measure the temperature of ytterbium and alkaline-earth-metal atoms confined in a magneto-optical trap (MOT). The method is based on the analysis of excitation spectra obtained by probing the

{}^{1}{\text{S}}_{0}\ensuremath{\rightarrow}{}^{3}{\text{P}}_{1}

intercombination line. Thanks to a careful analysis and modeling of the effects caused by the MOT light on the probe transition we overcome the resolution and precision limits encountered in previous works. Ground-state light shift and Rabi broadening are measured and successfully compared with calculated values. This knowledge allows us to properly extract the Doppler contribution to the linewidth, thus obtaining a reliable measurement of the cloud temperature. We finally show how spectroscopy on free-falling atoms provides an alternative method to determine the sample temperature which resembles the standard time-of-flight technique.

We report the basic idea and experimental demonstration of measuring the temperature of cold cesium atomic cloud confined in a magneto-optical trap (MOT) by analyzing absorption spectrum observed in the short-distance time-of-flight (TOF) method. Compared with the conventional TOF scheme, we measure the temperature of cold atomic cloud in MOT by short-distance TOF method for our small vapor cell. If the cold atomic cloud is released, it will fall and expand due to gravity and its initial velocity distribution. Utilizing a cylindrical resonant probe beam positioned several millimeters beneath the MOT (in this paper, we analyzed the cases for 3mm, 5mm, and 8mm of center-to-center distance between the MOT region and the probe beam, respectively), we can record the short-distance TOF absorption spectrum with a photodiode when cold atoms go through the probe region. Analysis of the short-distance TOF absorption spectrum yields the effective temperature of the cold cloud in MOT.

Based on the real sense of the time-of-flight , we demonstrate an alternative method of measuring the temperature of cold atoms in magneto-optical traps (MOTs) using a high-finesse optical microcavity, which acts as a pointlike single-atom counter. A cloud of atoms trapped in magneto-optical traps is positioned about 5 mm above the cavity, and the atoms fall freely down through the cavity. The temperature of the cold atoms in the MOT is determined by counting the exact arrival times of the single atoms. A theoretical model based on a ballistic expansion of a cloud of trapped atoms falling in the earth’s gravitational field is used to fit the probability distribution of atom arrivals, and the fittings agree very well with the experimental results. This method could be used for systems with little room, where an extra probe beam is hard to involve, or with fewer atoms initially.

We present measurements of polarization-gradient cooling in a Cs magneto-optic trap (MOT). The temperature in the MOT is found to vary linearly with the light shift. The slope gives a value of ${C}_{\ensuremath{\sigma}}=0.25\ifmmode\pm\else\textpm\fi{}0.05$ while the minimum temperature ${T}_{0}=3.8\ifmmode\pm\else\textpm\fi{}3.3\phantom{\rule{0.3em}{0ex}}\ensuremath{\mu}\mathrm{K}$, in agreement with measurements done in the absence of a magnetic field. The temperature is determined by using a nondestructive method which uses Rydberg time-of-flight velocity distributions of trapped atoms.

A differential two-photon spectroscopic technique for measurement of atomic temperatures in a working magneto-optical trap was demonstrated. We performed experimental and theoretical studies of two-photon resonances on Rydberg transitions 2S1/2−2P3/2−58S in cold Li7 atoms by using counter- and co-propagating laser beams. By analyzing the spectral shapes, a dependence of Rabi broadening and Doppler broadening on total intensity of cooling laser beams was obtained. We measured the temperature of Li7 atoms in the range from 0.25 to 0.75 mK. Our theoretical and experimental results are in reasonably good agreement. The developed approach for temperature measurements can be applied to cold atoms in different traps, including confined hydrogen and antihydrogen atoms.

We demonstrate a technique for spatially resolved temperature measurement utilizing Rydberg Doppler broadening thermometry. This method employs two focused laser beams arranged perpendicularly to excite laser-cooled atoms from the ground state to a Rydberg state via a two-photon absorption process. Temperature is obtained through Doppler broadening of the spectral line. The perpendicular configuration allows for selective probing of a specific position within the atomic cloud, enabling localized temperature measurement. This technique, in principle, offers a temperature resolution on the order of nK, attributed to the exceptionally narrow natural linewidth of the involved rubidium Rydberg transition line. Furthermore, the setup enables the measurement of position-velocity correlations within the cold atom ensemble. The velocity information is extracted through the Doppler shift, whereas the spatial information is inferred from the arrival time of ions detected by a channel electron multiplier detector. We use our method to measure the local temperature in a magneto-optical trap.