Sisyphus Cooling of Lithium

TL;DR

This paper demonstrates effective laser cooling of lithium atoms to sub-Doppler temperatures using Sisyphus cooling on both D1 and D2 lines, overcoming previous limitations related to hyperfine structure.

Contribution

It introduces a robust cooling method applicable to all alkali atoms, achieving lower temperatures with modest laser power and minimal sensitivity to experimental parameters.

Findings

Achieved temperatures as low as 40 μK, near the recoil limit.

Demonstrated cooling on both D1 and D2 lines for lithium.

Method is insensitive to laser power, polarization, detuning, and magnetic fields.

Abstract

Laser cooling to sub-Doppler temperatures by optical molasses is thought to be inhibited in atoms with unresolved, near-degenerate hyperfine structure in the excited state. We demonstrate that such cooling is possible in one to three dimensions, not only near the standard D2 line for laser cooling, but over a range extending to the D1 line. Via a combination of Sisyphus cooling followed by adiabatic expansion, we reach temperatures as low as 40 \mu K, which corresponds to atomic velocities a factor of 2.6 above the limit imposed by a single photon recoil. Our method requires modest laser power at a frequency within reach of standard frequency locking methods. It is largely insensitive to laser power, polarization and detuning, magnetic fields, and initial hyperfine populations. Our results suggest that optical molasses should be possible with all alkali species.