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arXiv:2607.09604

Characterisation of a strontium cold atom source using fluorescence spectroscopy and time-of-flight

Kamran Hussain, Hamza Labiad, A. L. Marchant, Jonathan N. Tinsley, T. Valenzuela, J. P. Coleman, David Newbold, Mark G. Bason

Published Jul 10, 2026• 0 citations
arXivHTMLPDF

Abstract

We demonstrate a characterisation methodology for a strontium atomic beam, produced by a two-dimensional magneto-optical trap and delivered via a resonant push beam, using fluorescence spectroscopy and time-of-flight (ToF). This provides insight into the beam characteristics of a cold atom source, allowing for direct measurement of the transverse velocity spread, longitudinal velocity distributions, divergence, and the capturable flux for further cooling. From the ToF measurements, we derive a series of flux-per-longitudinal-velocity distributions at varying push saturation parameters ($s_{\mathrm{push}}$) using both a unidirectional and counter-propagating resonant probe beam. A simulation-derived factor is applied to the unidirectional probe longitudinal velocity distribution to account for differences in the scattering rate scaling. The distributions are integrated up to an estimated 3D-MOT capture velocity of \SI{30}{\meter\per\second}. For our system, we find that at $s_{\mathrm{push}} = 0.45$, we obtain a flux of $(1.7 \pm 0.4)\times10^{8}$ atoms/s and $(1.5 \pm 0.4)\times10^{8}$ atoms/s, using a unidirectional probe beam and counter-propagating probe, respectively. These measurements provide a framework for characterising cold atomic sources for applications such as 3D MOT loading and atom interferometers.

DOI
10.48550/arxiv.2607.09604

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We demonstrate a characterisation methodology for a strontium atomic beam, produced by a two-dimensional magneto-optical trap and delivered via a resonant push beam, using fluorescence spectroscopy and time-of-flight (ToF). This provides insight into the beam characteristics of a cold atom source, allowing for direct measurement of the transverse velocity spread, longitudinal velocity distributions, divergence, and the capturable flux for further cooling. From the ToF measurements, we derive a series of flux-per-longitudinal-velocity distributions at varying push saturation parameters (spushs_{\mathrm{push}}spush​) using both a unidirectional and counter-propagating resonant probe beam. A simulation-derived factor is applied to the unidirectional probe longitudinal velocity distribution to account for differences in the scattering rate scaling. The distributions are integrated up to an estimated 3D-MOT capture velocity of \SI{30}{\meter\per\second}. For our system, we find that at spush=0.45s_{\mathrm{push}} = 0.45spush​=0.45, we obtain a flux of (1.7±0.4)×108(1.7 \pm 0.4)\times10^{8}(1.7±0.4)×108 atoms/s and (1.5±0.4)×108(1.5 \pm 0.4)\times10^{8}(1.5±0.4)×108 atoms/s, using a unidirectional probe beam and counter-propagating probe, respectively. These measurements provide a framework for characterising cold atomic sources for applications such as 3D MOT loading and atom interferometers.
We report on the realization of a transversely loaded two-dimensional magneto-optical trap serving as a source for cold strontium atoms. We analyze the dependence of the source's properties on various parameters, in particular the intensity of a pushing beam accelerating the atoms out of the source. An atomic flux exceeding 109atoms/s{10}^{9}\phantom{\rule{0.28em}{0ex}}\mathrm{atoms}/\mathrm{s}109atoms/s at a rather moderate oven temperature of $500{\phantom{\rule{0.16em}{0ex}}}^{\ensuremath{\circ}}\mathrm{C}$ is achieved. The longitudinal velocity of the atomic beam can be tuned over several tens of m/s by adjusting the power of the pushing laser beam. The beam divergence is around 60 mrad, determined by the transverse velocity distribution of the cold atoms. The slow atom source is used to load a three-dimensional magneto-optical trap realizing loading rates up to 109atoms/s{10}^{9}\phantom{\rule{0.16em}{0ex}}\mathrm{atoms}/\mathrm{s}109atoms/s without indication of saturation of the loading rate for increasing oven temperature. The compact setup avoids undesired effects found in alternative sources like, e.g., Zeeman slowers, such as vacuum contamination and black-body radiation due to the hot strontium oven.
We present an experimental set-up for the production of a beam source of cold 87Rb atoms, which is formed from a trapped cold atomic cloud in a three-dimensional (3D) magneto-optical trap (MOT). Via a radiation pressure difference generated by a specially designed leak tunnel along one trapping laser beam, the atoms are pushed out continuously with low velocity and high flux. The beam was measured to have a mean velocity of 12m/s and a longitudinal velocity spread of about 3m/s under nominal experimental conditions, based on the fluorescence and the time of flight (TOF) technologies. And its flux can be tuned by adjusting the MOT parameters from 108 to 109 atoms/s. Especially the beam performance dependence on trapping laser detuning and power is experimentally studied.
A beam source is proposed for the production of an intense cold cesium atomic beam that can be used in cesium beam atomic clocks. The source is based on a two-dimensional magneto-optical trap (2D-MOT), but introduces hollow cooling and pushing lights in the axial direction to create a 2D+-MOT, which separates the cooling and pushing functions while the low-power pushing light pushes atoms out to form a cold atomic beam. This cold cesium atomic beam source reduces the light shift due to leakage light and retains longitudinal cooling to increase the flux of the cold atomic beam compared with that of the conventional 2D+-MOT scheme. The specifics of the design are investigated, the atomic velocity and beam flux are calculated, and the results are experimentally verified. The results demonstrate that when the power of the pushing light is 180 µW and when its frequency resonates with the 4 → 5′ transition of the Cs D2 line, the most probable longitudinal velocity of the outgoing cold atomic beam, the width of velocity distribution, and the atomic beam flux are 19.38 m/s, 8.1 m/s, and 1.7 × 1010 atoms/s, respectively.
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.
In this paper we report on the first purely ``pump-probe'' nonlinear laser spectroscopy results in a slow atomic beam. We have observed Raman, Rayleigh, and recoil-induced resonances (RIR) in a continuous beam of slow and cold cesium atoms extracted from a two-dimensional (2D) magneto-optical-trap (MOT) with the moving molasses technique. The RIR enabled us to measure the velocity distribution, therefore the average speed (0.6--4 m/s) and temperature (50--500 \ensuremath{\mu}K) of the atomic beam. Compared to time of flight, this technique has the advantage of being local, more sensitive in the low-velocity regime (v<1m/s),(v<1 \mathrm{m}/\mathrm{s}),(v<1m/s), and it gives access to transverse velocities and temperatures. Moreover, it may be extended to measure atomic velocities in the 2D MOT source of the atomic beam.
We present a high-flux source of cold strontium atoms based on a two-dimensional magneto-optical trap (2D MOT) and a Zeeman slower. We use the source to load a 3D MOT in a separate science chamber, observing a loading rate of 4×1010 atoms/s—to our knowledge, the highest reported loading flux for strontium. To characterize the vacuum pressure in the science chamber, we load the atoms into a magnetic trap and measure a lifetime of between 8 and 24 s, depending on the oven temperature. Finally, we characterize the atom flux and velocity distributions from the oven and from the 2D MOT source, finding reasonable agreement with models in the free molecular flow regime. Our results show that it is possible to readily produce a cold strontium flux at comparable levels to those of alkali species, at oven temperatures compatible with long-term operation, and at vacuum pressures suitable for state-of-the-art quantum experiments. We make our design available at no cost to benefit researchers in the quantum community.