Diffusion of Rb atoms in paraffin-coated resonant vapor cells

Abstract

Abstract. We present the results of a study of the diffusion of Rb atoms in paraffin -coated resonant vapor cells. We have modeled the Rb diffusion both in the cell and in the coating, assuming that the main loss of Rb atoms is due to the physical absorption of the atoms by the glass substrate. It is demonstrated that the equilibrium atomic density in the cell is a monotonic function of the thickness of the paraffin coating: the density increases with an increase in the thickness of the coating. The diffusion coefficient for rubidium in paraffin thin films has been determined to be equal to 4.7  10 -7 cm 2 /s. The results of the experiment might be useful for a better understanding of the details involved in the processes of the interaction of alkali atoms with a paraffin coating and atomic diffusion in resonant vapor cells.

Paraffin coated rubidium cell with an internal atomic vapor source

“…The value of the diffusion coefficient measured is equal within an error bar to the paraffin diffusion coefficient 5 × 10 −7 cm 2 /s that was measured in Ref. [13] and to the paraffin (n-Octadecane) self-diffusion coefficient 4.6 × 10 −7 cm 2 /s that was measured in reference [19].…”

“…Then the atoms, after many bounces in the cell, start to diffuse deep inside the coating towards the glass substrate surface, where they are irreversibly absorbed. Not that, it takes rather long time to collect several equilibrium mono-layers of atoms on the glass substrate and obtain truly steady-state atomic density in common resonant cells [13,16].…”

“…In the case of a cell, constructed as a spherical bulb with cylindrical capillary, the time of preserving of the atomic coherences is linear function of diameter of the bulb, while the leaking time of the atoms scales as a cubic of diameter of the bulb [13]. Under these conditions the escape time is relatively insignificant in big cells, but it becomes much more important in small cells, when the diameter of the bulb is the same order of diameter of the capillary.…”

Calibration of Spin-Light Coupling by Coherently Induced Faraday Rotation

“…At the same time, the incoherent part will depend on motion and wall collisions. It has been shown that even in the paraffin-or alkene-coated cells [34][35][36][37] or cells with dilute buffer gas [38] the atomic motion can be effectively described by the diffusion equation with adequate wall boundary condition. The cells with coated walls will feature a slow decay for the flat mode (𝑢 0 (x 𝑖 ) = 1/ √ 𝑉) which depends on intrinsic dynamics and wall decay, and much faster decay for all other modes, which given by 𝛾 𝑛 S = 𝐷 𝑘 2 𝑛 , where 𝐷 is the effective diffusion constant and 𝑘 𝑛 is the characteristic wavenumber of 𝑛-th mode [22].…”