High-Flux Beam Source for Cold, Slow Atoms or Molecules

We demonstrate and characterize a high-flux beam source for cold, slow atoms or molecules. The desired species is vaporized using laser ablation, then cooled by thermalization in a cryogenic cell of buffer gas. The beam is formed by particles exiting a hole in the buffer gas cell. We characterize the properties of the beam (flux, forward velocity, temperature) for both an atom (Na) and a molecule (PbO) under varying buffer gas density, and discuss conditions for optimizing these beam parameters. Our source compares favorably to existing techniques of beam formation, for a variety of applications.

Figure 1

A schematic of the beam apparatus. When detecting fluorescence, a lens (not shown) collimates a fraction of the fluorescence light and directs it out a window to a PMT.

Figure 2

The number of cold $A$ particles, $N_h$, that emerge in the beam as a function of $n_{\mathrm{He}}$. Curves with specific functional forms have been inserted to show the different scaling regimes. The intersection of the curves corresponds to the condition $R=R_h$, where a typical $A$ particle is thermalized just as it reaches the hole.

Figure 3

PbO and Na beam mean forward velocities, $v_f$, as a function of $n_{\mathrm{He}}$. Extrapolation of the data to zero buffer gas density is illustrated by best-fit lines (dashed lines).

Figure 4

PbO and Na temperatures as a function of $n_{\mathrm{He}}$ as determined by fits to spectral profiles. “Transverse,” “longitudinal,” and “in cell” refer to the location of the probe laser (see Fig. 1). Typical errors for the transverse and in cell Na temperatures are comparable to the marker size.