Continuous loading of magneto-optical trap of Rb at narrow transition

TL;DR

This paper demonstrates a method for continuously loading a narrow-linewidth magneto-optical trap of rubidium-87 atoms using a combined blue and infrared laser setup, enabling efficient accumulation of cold atoms.

Contribution

The authors introduce a novel continuous loading technique for a narrow-linewidth blue MOT of Rb atoms using superimposed laser beams, supported by a theoretical framework.

Findings

Loaded approximately 10^8 atoms in 2.5 seconds.

Blue laser cooling lowers atom temperature even with broad IR laser present.

Optimal loading occurs when the blue laser overfills the IR beam spot.

Abstract

We report continuous loading of $^{\textrm{87}}$Rb atoms in a magneto-optical trap (MOT) at narrow linewidth, 420 nm 5S$_{1/2}$, F$=2\rightarrow$ 6P$_{3/2}$, F$=3$ blue transition (blue MOT). Continuous loading of the blue MOT is achieved by superimposing the blue laser beam, inside a hollow core of infrared laser beam driving the broad 5S$_{1/2}$, F$=2\rightarrow$ 5P$_{3/2}$, F$=3$ transition at 780 nm. We typically load $\sim10^{8}$ atoms in the blue MOT in 2.5 seconds. We characterize the continuous loading of blue MOT with various parameters such as magnetic field gradient, detuning, power and diameter of blue MOT beam and diameter of the hollow core (spot) inside the IR MOT beam. We observe that the blue laser beam should overfill the spot of the IR laser beam. This is because the blue laser cools the atoms to a lower temperature even in the presence of the broad IR laser i.e. in the overlapped region and hence helps in loading. We also present the theoretical framework for cooling atoms in the presence of simultaneously two transitions to support the experimental result. This method of continuous loading of the blue MOT can be useful to produce a continuous atomic beam of cold Rb atoms.