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Optics Express

Continuous cold rubidium atomic beam with enhanced flux and tunable velocity

Shengzhe Wang, Zhixin Meng, Peiqiang Yan, Yuanxing Liu, Yanying Feng

Published Jan 31, 2024• 5 citations
Publisher

Abstract

, a mean velocity of 10.96(2.20) m/s, and a transverse temperature of 16.90(1.56) µK. Investigating the influence of high cooling laser intensity, we observe a significant population loss of atoms to hyperfine-level dark states. To account for this, we employ a multiple hyperfine level model to calculate the cooling efficiency associated with the population in dark states, subsequently modifying the scattering force. Simulations of beam flux at different cooling and repumping laser intensities using the modified scattering force are in agreement with experimental results. Optimizing repumping and cooling intensities enhances the flux by 50%. The influence of phase modulation on both the pushing and cooling lasers is experimentally studied, revealing that the mean velocity of cold atoms can be tuned from 9.5 m/s to 14.6 m/s with a phase-modulated pushing laser. The versatility of this continuous beam source, featuring high flux, controlled velocity, and narrow transverse temperature, renders it valuable for applications in atom interferometers and clocks, ultimately enhancing bandwidth, sensitivity, and signal contrast in these devices.

DOI
10.1364/oe.516508

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, a mean velocity of 10.96(2.20) m/s, and a transverse temperature of 16.90(1.56) µK. Investigating the influence of high cooling laser intensity, we observe a significant population loss of atoms to hyperfine-level dark states. To account for this, we employ a multiple hyperfine level model to calculate the cooling efficiency associated with the population in dark states, subsequently modifying the scattering force. Simulations of beam flux at different cooling and repumping laser intensities using the modified scattering force are in agreement with experimental results. Optimizing repumping and cooling intensities enhances the flux by 50%. The influence of phase modulation on both the pushing and cooling lasers is experimentally studied, revealing that the mean velocity of cold atoms can be tuned from 9.5 m/s to 14.6 m/s with a phase-modulated pushing laser. The versatility of this continuous beam source, featuring high flux, controlled velocity, and narrow transverse temperature, renders it valuable for applications in atom interferometers and clocks, ultimately enhancing bandwidth, sensitivity, and signal contrast in these devices.
We present a cold atomic beam source based on a two-dimensional (2D)+ magneto-optical trap (MOT), capable of generating a continuous cold beam of 87Rb atoms with a flux up to 4.3*10^9 atoms/s, a mean velocity of 10.96(2.20) m/s, and a transverse temperature of 16.90(1.56) uK. Investigating the influence of high cooling laser intensity, we observe a significant population loss of atoms to hyperfine-level dark states. To account for this, we employ a multiple hyperfine level model to calculate the cooling efficiency associated with the population in dark states, subsequently modifying the scattering force. Simulations of beam flux at different cooling and repumping laser intensities using the modified scattering force are in agreement with experimental results. Optimizing repumping and cooling intensities enhances the flux by 50%. The influence of phase modulation on both the pushing and cooling lasers is experimentally studied, revealing that the mean velocity of cold atoms can be tuned from 9.5 m/s to 14.6 m/s with a phase-modulated pushing laser. The versatility of this continuous beam source, featuring high flux, controlled velocity, and narrow transverse temperature, renders it valuable for applications in atom interferometers and clocks, ultimately enhancing bandwidth, sensitivity, and signal contrast in these devices.
We investigate experimentally and numerically the quantitative dependence of characteristics of a low-velocity intensity source (LVIS) of atomic beam on light parameters, especially the polarization of cooling laser along the atomic beam axis (pushing beam). By changing the polarization of the pushing beam, the longitudinal mean velocity of a rubidium atomic beam can be tuned continuously from 10 to 20 m/s and the flux can range from 3 × 10 8 to 1 × 10 9 atoms/s, corresponding to the maximum sensitivity of the velocity with respect to the polarization angle of 20 (m/s)/rad and the mean sensitivity of flux of 1.2 × 10 9 (atoms/s)/rad. The mechanism is explained with a Monte-Carlo based numerical simulation method, which shows a qualitative agreement with the experimental result. This is also a demonstration of a method enabling the fast and continuous modulation of a low-velocity intense source of cold atomic beam on the velocity or flux, which can be used in many fields, like the development of a cold atomic beam interferometer and atom lithography.
We present the implementation and characterization of a slow, intense, and collimated rubidium atomic source for atom interferometry. The continuous87Rb cold atomic beam is produced by a new compact two-dimensional magneto-optical trap. And it is based on the 2D+MOT design but a much smaller size and a higher flux compared to our original LVIS system. The on-line detecting system developed over a combination of time-of-flight and fluorescence methods is used to optimize the beam parameters. The dependence of the beam flux on detuning and power are investigated in detail respectively, for cooling and pushing laser. The re-pumping laser power influence is also considered. With aError! Reference source not found.10 G/cm magnetic gradient, 3ΓError! Reference source not found. red detuning from resonance for cooling laser and 5ΓError! Reference source not found. red detuning for pushing laser, the obtained cold atomic beam has a high flux of 4.7×109atoms/s Error! Reference source not found. Error! Reference source not found. It has a narrow longitudinal velocity distribution with mean velocity 10 m/s and full width at half maximum (FWHM)Error! Reference source not found.2 m/sError! Reference source not found. The two-photo stimulated Raman transitions both in Doppler-free and Doppler-sensitive modes are first proceeded, and stable Raman-Ramsey fringes are achieved with twon/2 Error! Reference source not found. Raman pulses.
We present a compact, two-stage atomic beam source that produces a continuous, narrow, collimated, and high-flux beam of rubidium atoms with sub-Doppler temperatures in three dimensions, which features very low emission of near-resonance fluorescence along the atomic trajectory. The atom-beam source originates in a pushed two-dimensional magneto-optical trap (2D+2{\mathrm{D}}^{+}2D+ MOT) feeding a slightly off-axis three-dimensional moving optical-molasses stage that continuously cools and redirects the atom beam. The capture velocity of the moving optical molasses is deliberately chosen to be low, approximately 3m/s3\phantom{\rule{0.2em}{0ex}}\mathrm{m}/\mathrm{s}3m/s, to reduce fluorescence, and the cooling light is detuned by several atomic linewidths from resonance to reduce the absorption cross section of cooling-induced fluorescence. Near-resonance light from the 2D+2{\mathrm{D}}^{+}2D+ MOT and the push beam does not propagate to the output atomic trajectory due to a ${10}^{\ensuremath{\circ}}$ bend in the atomic trajectory. The atomic beam emitted from the two-stage source has a flux up to $1.6(3)\ifmmode\times\else\texttimes\fi{}{10}^{9}\phantom{\rule{0.2em}{0ex}}\mathrm{atoms}/\mathrm{s}$, with an optimized temperature of $15.0(2)\phantom{\rule{0.2em}{0ex}}\ensuremath{\mu}\mathrm{K}$. We employ continuous Raman-Ramsey interference measurements at the atom-beam output to study the sources of decoherence in the presence of continuous cooling, and demonstrate that the atom-beam source effectively preserves high fringe contrast even during cooling. This cold-atom-beam source is appropriate for use in atom interferometers and clocks, where continuous operation eliminates dead time, the slow atom-beam velocity (6--16 m/s) improves sensitivity, the narrow 3D velocity distribution improves fringe contrast, and the low reabsorption of scattered light mitigates decoherence caused by the continuous cooling process.
We discuss the implementation and characterization of the source of a slow, intense, and collimated beam of rubidium atoms. The cold atomic beam is produced by two-dimensional magneto-optical trapping in directions transverse to the atomic beam axis and unbalanced Doppler cooling in the axial direction. The vacuum design allows use of relatively low laser power and a considerably simplified assembly. The atomic beam has a high flux of about $2\ifmmode\times\else\texttimes\fi{}{10}^{10}\phantom{\rule{0.3em}{0ex}}\mathrm{atoms}∕\mathrm{s}$ at a total cooling laser power of 55mW55\phantom{\rule{0.3em}{0ex}}\mathrm{mW}55mW. It has a narrow longitudinal velocity distribution with mean velocity 15m∕s15\phantom{\rule{0.3em}{0ex}}\mathrm{m}∕\mathrm{s}15m∕s with full width at half maximum 3.5m∕s3.5\phantom{\rule{0.3em}{0ex}}\mathrm{m}∕\mathrm{s}3.5m∕s and has a low divergence of 26mrad26\phantom{\rule{0.3em}{0ex}}\mathrm{mrad}26mrad. The high flux enables ultrafast loading of about 1010{10}^{10}1010 atoms into a three-dimensional (3D) magneto-optical trap within 500 ms. The variation of the atomic beam flux was studied as a function of the rubidium vapor pressure, cooling laser power, transverse cooling laser beam length, detuning of the cooling laser, and relative intensities of the cooling beams along the atomic beam axis. We also discuss a detailed comparison of our measurements of the cold atomic beam with a 3D numerical simulation.
To achieve a primary frequency standard based on a continuous fountain of laser cooled cesium atoms, we report on the production of a bright, slow and cold continuous atomic beam. Atoms are cooled from a thermal vapor in a 45/spl deg/ laser geometry and launched directly from the optical molasses by the moving molasses technique. The effects of the source fluorescence on the continuous beam (average velocity, temperature and flux) have been observed, and ways to optimize simultaneously the atomic capture and the continuous beam are presented. Flux measurements rise to 2/spl times/10/sup 8/ at/s from a 2D magneto-optical trap at 7 m/s. The initial velocity is easily tunable from 1 to 10 m/s. If the longitudinal temperature is about 70 /spl mu/K, additional transverse cooling even reduces the transverse temperature in one dimension below 30 /spl mu/K. By extrapolating the obtained atomic flux to the continuous fountain under construction, we expect a short-term stability of 7/spl times/10/sup -14//spl tau//sup -1/2/. Other applications of continuous beams of cold atoms are suggested.