arXiv:1811.02185 · SciPost Physics

Sub-Doppler laser cooling of $^{39}$K via the 4S$\to$5P transition

Govind Unnikrishnan, Michael Gröbner, Hanns‐Christoph Nägerl

Published Apr 18, 2019• 6 citations

Abstract

We demonstrate sub-Doppler laser cooling of ^{39} 39 K using degenerate Raman sideband cooling via the 4S _{1/2} \rightarrow 1 / 2 → 5P _{1/2} 1 / 2 transition at 404.8 nm. By using an optical lattice in combination with a magnetic field and optical pumping beams, we obtain a spin-polarized sample of up to 5.6 \times 10^{7} 5.6 × 10 7 atoms cooled down to a sub-Doppler temperature of 4 \upmu μ K, reaching a peak density of 3.9 \times 10^{9} 3.9 × 10 9 atoms/cm ^{3} 3 , a phase-space density greater than 10^{-5} 10 − 5 , and an average vibrational level of \langle \nu \rangle=0.6 ⟨ ν ⟩ = 0.6 in the lattice. This work opens up the possibility of implementing a single-site imaging scheme in a far-detuned optical lattice utilizing shorter wavelength transitions in alkali atoms, thus allowing improved spatial resolution.

DOI: 10.21468/scipostphys.6.4.047

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arXiv:1811.02185 · SciPost Physics

Sub-Doppler laser cooling of $^{39}$ K via the 4S$\to$5P transitionSub-Doppler laser cooling of $^{39}$K via the 4S$\to$5P transition

Govind Unnikrishnan, Michael Gröbner, Hanns‐Christoph Nägerl

Published Apr 18, 2019• 6 citations

arXiv HTML PDF

Abstract

DOI: 10.21468/scipostphys.6.4.047

Related papers

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Sub-Doppler laser cooling of

^{39}

K via the 4S$\to$5P transition

We report on a realization of sub-Doppler laser cooling of

^{39}\mathrm{K}

atoms using degenerate three-dimensional Raman sideband cooling. We take advantage of the well-resolved excited hyperfine states on the

{D}_{1}

optical transition to produce spin-polarized samples with $1.4\ifmmode\times\else\texttimes\fi{}{10}^{8}$ atoms at temperatures of 1.8 $\ensuremath{\mu}\mathrm{K}$. The phase-space densities are $\ensuremath{\ge}{10}^{\ensuremath{-}4}$, which significantly improves the initial conditions for a subsequent evaporative cooling step. The presented cooling technique using the

{D}_{1}

line can be adapted to other atomic species and is applicable to high-resolution imaging schemes in far off-resonant optical lattices.

We report on the implementation of degenerate Raman sideband cooling of

^{40}\mathrm{K}

atoms. The scheme incorporates a three-dimensional (3D) optical lattice, which confines the atoms and drives the Raman transitions. The optical cooling cycle is closed by two optical pumping beams. The wavelength of the laser beams forming the lattice is close to the

{\mathrm{D}}_{2}

atomic transition, while the optical pumping is operated near the

{\mathrm{D}}_{1}

transition. With this cooling method, we achieve a temperature of $\ensuremath{\sim}1\phantom{\rule{0.16em}{0ex}}\ensuremath{\mu}\mathrm{K}$ of a cloud with $\ensuremath{\sim}{10}^{7}$ atoms. This corresponds to a phase space density of $\ensuremath{\ge}{10}^{\ensuremath{-}3}$. Moreover, the fermionic ensemble is spin polarized to conditions which are favorable for subsequent evaporative cooling. We study the dependence of the cooling scheme on several parameters, including the applied magnetic field and the detuning, duration, and intensity profile of the optical pumping beams. Adding this optical cooling stage to current Fermi gas experiments can improve the final conditions and increase the data rate.

23%

of the sites are occupied,

95%

of the atoms are in the lowest energy magnetic sublevel, and

37%

are in the lowest 3D vibrational state.

{}^{39}

K and

{}^{41}

K, respectively. Our findings should find application to other atomic systems.