Chirped magneto-optical trap of molybdenum

Abstract

We have directly loaded a cryogenic beam of molybdenum atoms into a magneto-optical trap. By chirping the detuning of the trapping lasers, we were able to enhance the number of atoms loaded into the trap by more than a factor of two. We optimize the trapped samples for atom number, temperature, and lifetime by varying the laser-cooling parameters. The laser-cooled molybdenum atoms are subsequently transferred to a magnetic trap where we achieve vacuum-limited lifetimes of 100\,ms. Comparison of magneto-optical trap and magnetic trap lifetimes allow us to extract partial decay rates of the $\text{z}\,^7\text{P}^\text{o}_4\rightarrow\text{a}\,^5\text{D}_4$ and $\text{z}\,^7\text{P}^\text{o}_4\rightarrow\text{a}\,^5\text{D}_3$ transitions. We also provide measurements of the isotope shifts for the $\text{a}\,^7\text{S}_3\rightarrow \text{z}\,^7\text{P}^\text{o}_4$ transition with up to four times better precision than previously reported. Finally, we discuss the prospect of applying the chriped magneto-optical trap to produce laser-cooled samples of MgF.

Figures (8)

• Figure 1: Schematic of the experimental apparatus. The cubic chamber on the left houses the CBGB source, and the octagonal chamber on the right houses the MOT. Six circular polarized laser beams (two vertical beams are not shown) together with two electromagnets in an anti-Helmholtz configuration (not shown) generate the MOT. We detect fluorescence from the atomic beam or the MOT via a photomultiplier tube (PMT) or an electron multiplying charge-coupled device (EMCCD) camera.
• Figure 2: Level diagram with electronic states that are relevant for laser cooling molybdenum. The main cycling transition occurs between the $\text{a}\,^7\text{S}_3$ and the $\text{z}\,^7\text{P}^\text{o}_4$ states. From the $\text{z}\,^7\text{P}^\text{o}_4$ state, there are leaks to lower-lying $\text{a}\,^5\text{D}_4$ and $\text{a}\,^5\text{D}_3$ states. We do not show twelve intermediate states in addition to $\text{a}\,^5\text{D}_{2}$, $\text{a}\,^5\text{D}_1$, and $\text{a}\,^5\text{D}_0$ states; decays to these states from $\text{z}\,^7\text{P}_4^\text{o}$ are either E1 forbidden, too weak to be observed given our statistical precision and vacuum-limited lifetime, or forbidden by angular momentum and parity selection rules.
• Figure 3: Atomic beam absorption as a function of probe frequency $\nu$ referenced to the ^98 Mo $\text{a}\,^7\text{S}_3\rightarrow \text{z}\,^7\text{P}^\text{o}_4$ transition frequency $\nu_{98}$. The red curve is a fit to the sum of five Voigt profiles. The inset depicts a time trace when the probe beam is nearly resonant with the ^98 Mo $\text{a}\,^7\text{S}_3\rightarrow \text{z}\,^7\text{P}^\text{o}_4$ transition. Error bars representing the standard error in the mean of multiple repetitions are typically the size of the points.
• Figure 4: (a) Laser-induced fluorescence (LIF) of the ^98 Mo beam in the MOT region as a function of time after the ablation pulse and laser frequency, the latter determining the velocity probed through the Doppler shift. The white curve indicates the arrival time of an atom that was created at $t = 0$ with velocity $v$. The inset in the upper right shows the cumulative distribution function (CDF) of velocities in the atomic beam. The faint streak on the lower left is likely due to fast atoms of another isotope. (b) Exemplary frequency chirp of the MOT beam detuning.
• Figure 5: (a--e) MOT images for all stable bosonic isotopes of molybdenum. Here, the final MOT detuning was $\Delta_f = -2\Gamma$, the six beam saturation parameter was $s = 10$, and the axial gradient was $B'_z=3mT/cm$, and no repump laser is present. The numbers of atoms in each image from left to right are approximately $3\times 10^3$, $4\times 10^3$, $5\times 10^3$, $3\times 10^3$, and $5\times 10^3$. (f--j) LIF signal from molybdenum beams detected in the MOT region as a function of detuning from the ^98 Mo $\text{a}\,^7\text{S}_3\rightarrow \text{z}\,^7\text{P}^\text{o}_4$ transition.