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Laser Physics

Differential two-photon spectroscopic measurements of cold atoms temperature with variable angle between probe beams

Boris B. Zelener, E V Vilshanskaya, Sergey A. Saakyan, I. D. Arshinova, Andrey A. Bobrov, Vladimir A. Sautenkov, B. V. Zelener

Published Jan 9, 2020• 1 citation
Publisher

Abstract

Abstract In this work, the differential two-photon spectroscopy with an adjustable angle between the beams is used for measurement of atomic temperatures in a working 40 Ca magneto-optical trap. It is demonstrated that it is possible to improve the accuracy of temperature measurements by selecting different angles. Experimental and theoretical studies of two-photon Rydberg transitions 4s 2 1 S 0 —50 1 S 0 in cold 40 Ca atoms by means of counter-propagating laser beams and laser beams with different angles are performed. By analyzing the spectral shapes, a dependence of Doppler broadening on frequency detuning of cooling laser beams is obtained. We have measured the temperature of 40 Ca atoms in the range from 4 to 8 mK for different values of the cooling laser detuning.

DOI
10.1088/1555-6611/ab632f

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Abstract In this work, the differential two-photon spectroscopy with an adjustable angle between the beams is used for measurement of atomic temperatures in a working 40 Ca magneto-optical trap. It is demonstrated that it is possible to improve the accuracy of temperature measurements by selecting different angles. Experimental and theoretical studies of two-photon Rydberg transitions 4s 2 1 S 0 —50 1 S 0 in cold 40 Ca atoms by means of counter-propagating laser beams and laser beams with different angles are performed. By analyzing the spectral shapes, a dependence of Doppler broadening on frequency detuning of cooling laser beams is obtained. We have measured the temperature of 40 Ca atoms in the range from 4 to 8 mK for different values of the cooling laser detuning.
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.
Our work is devoted to theoretical study of the two-photon coherent spectroscopy of 7 Li atoms continuously cooled in a magneto-optical trap (MOT) on the 2S–2P transition. The ultracold atoms are transferred to highly excited Rydberg states in a two-step coherent excitation process by red and UV lasers. The red laser is detuned by -600 MHz from 2S–2P transition frequency and UV laser frequency detuning is scanned in the vicinity of +600 MHz from 2P-nS(D) transition where n∼40-100 is principal quantum number. The fluorescence signal on the 2P–2S cooling transition makes it possible to obtain a two-photon absorption spectrum. Atom-field interaction is considered in the simple three-level approximation involving a density matrix formalism. It is shown that the effect of the MOT beams on the shape of the two-photon absorption line can be taken into account by an appropriate change in the 2S–nS(D) coherence decay rate.
The spectra of highly excited 40 Ca atoms prepared using a magneto-optical trap and an ultraviolet laser are experimentally studied. The dependence of the atomic density in the magneto-optical trap on the detuning frequency of cooling radiation and on the magnetic field gradient is determined. By using the technique based on the reduction of resonance fluorescence, the energy of the 76 1 S 0 Rydberg state for 40 Ca atoms is determined. A new scheme for stabilization of the laser frequency to create highly excited Rydberg atoms is demonstrated. This scheme employs the saturated absorption spectrum in a cell with rubidium atomic gas.