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

Govind Unnikrishnan, Michael Gröbner, Hanns-Christoph Nägerl

SciPost Phys. 6, 047 (2019) · published 18 April 2019

### Abstract

We demonstrate sub-Doppler laser cooling of $^{39}$K using degenerate Raman sideband cooling via the 4S$_{1/2} \rightarrow$5P$_{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 $5.6 \times 10^{7}$ atoms cooled down to a sub-Doppler temperature of 4 $\mu$K, reaching a peak density of $3.9 \times 10^{9}$ atoms/cm$^{3}$, a phase-space density greater than $10^{-5}$, and an average vibrational level of $\langle \nu \rangle=0.6$ 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.

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