Hyperfine and Zeeman Optical Pumping and Transverse Laser Cooling of a Thermal Atomic Beam of Dysprosium Using a Single 421 nm Laser

Abstract

We demonstrate the effect of Zeeman and hyperfine optical pumping and transverse laser cooling of a dysprosium (Dy) atomic beam on the $4f^{10}6s^2(J = 8) \rightarrow 4f^{10}6s6p(J = 9)$ transition at 421.291 nm. For $^{163}$Dy, an electro-optic modulator is used to generate five frequency sidebands required to pump the atoms to the $F = 10.5$ ground state hyperfine level and the light polarization is chosen to pump the atoms to the $m_F = 10.5$ Zeeman sublevel. The atoms are simultaneously laser-cooled using a standing wave orthogonal to the atomic beam. The resulting polarized and cooled atomic beam will be used in fundamental physics experiments taking advantage of the accidental degeneracy of excited states in Dy including the ongoing measurement of parity violation in this system.

Figures (12)

• Figure 1: Simplified schematic of the experimental setup. In the figure EOM is the Electro-Optic Modulator, PBS is the Polarising Beamsplitter, $\lambda/2$ and $\lambda/4$ are the half and quarter waveplates, PMT is the photomultiplier tube, UHV chamber is the ultra-high vacuum chamber, and B is the magnetic field defining the quantization axis. Of the two separate Fabry-Perot interferometers in the figure, one is used to lock the fundamental laser frequency of the 421 nm laser and the second as a Fabry-Perot spectrum analyser for the second harmonic.
• Figure 2: Diagram of the energy level of dysprosium representing the nearly degenerate pair of opposite parity states A and B. The diagram shows the transitions used in this work to pump and probe the ground state, respectively 421 and 599 nm, as well as the transitions used for the B state preparation, 833 and 669 nm, and the 564 nm fluorescence detection of the parity signal. The A and B states are mixed with a RF field.
• Figure 3: Schematic for optical pumping of $^{163}$Dy on the 421 nm $J=8\rightarrow J=9$ transition. Once excited to an $F$ hyperfine state of the excited state, the atoms can generally decay to the $F-1, F$ and $F+1$ ground hyperfine states (if these are available), with the latter being the weakest due to the $\Delta F = \Delta J$ rule auzinsh2010opticallypolarisedatoms. We only show the $\Delta F=0$ decays in the figure.
• Figure 4: Fabry-Perot spectrum analyzer signal with no modulation, optimal-power modulation for optical pumping and maximum RF powers for modulation (see text).
• Figure 5: Fluorescence $\sigma_+$ probe spectra with pump powers of 0 mW and 230 mW. A vanishing $^{164}$Dy spectral line indicates optimized polarization of the pump laser. Residual oscillations of amplitude in the probe spectrum are observed after optical pumping.