$\Lambda$-enhanced gray molasses in a tetrahedral laser beam geometry

TL;DR

This paper demonstrates sub-Doppler cooling of lithium atoms using a novel tetrahedral laser beam setup generated by a nanofabricated diffraction grating, achieving significant cooling and trapping efficiency for quantum applications.

Contribution

It introduces a new tetrahedral laser beam geometry for gray molasses cooling, expanding the methods for efficient cold atom production with grating magneto-optical traps.

Findings

Captured 11% of lithium atoms into the molasses

Achieved atom temperatures of 60 μK radially and 23 μK axially

Cooling is effective only near Raman resonance, as confirmed by simulations

Abstract

We report observation of sub-Doppler cooling of lithium using an irregular-tetrahedral laser beam arrangement, which is produced by a nanofabricated diffraction grating. We are able to capture 11(2) % of the lithium atoms from a grating magneto-optical trap into $\Lambda$-enhanced $D_1$ gray molasses. The molasses cools the captured atoms to a radial temperature of 60(9) $\mu$K and an axial temperature of 23(3) $\mu$K. In contrast to results from conventional counterpropagating beam configurations, we do not observe cooling when our optical fields are detuned from Raman resonance. An optical Bloch equation simulation of the cooling dynamics agrees with our data. Our results show that grating magneto-optical traps can serve as a robust source of cold atoms for tweezer-array and atom-chip experiments, even when the atomic species is not amenable to sub-Doppler cooling in bright optical molasses.