Controlling atomic vapor density in paraffin-coated cells using light-induced atomic desorption

Atomic-vapor density change due to light induced atomic desorption (LIAD) is studied in paraffin-coated rubidium, cesium, sodium, and potassium cells. In the present experiment, low-intensity probe light is used to obtain an absorption spectrum and measure the vapor density, while light from an argon-ion laser, array of light emitting diodes, or discharge lamp is used for desorption. Potassium is found to exhibit significantly weaker LIAD from paraffin compared to Rb and Cs, and we were unable to observe LIAD with sodium. A simple LIAD model is applied to describe the observed vapor-density dynamics, and the role of the cell’s stem is explored through the use of cells with lockable stems. Stabilization of Cs vapor density above its equilibrium value over $25\min$ is demonstrated. The results of this work could be used to assess the use of LIAD for vapor-density control in magnetometers, clocks, and gyroscopes utilizing coated cells.

Figure 1

Typical LIAD signal and a model fit. The times when the desorption light is turned on and off are denoted as $t_0$ and $t_{\text{off}}$. The initial $n_0$, maximum $n_{\max }$, and $n\left(t_{\text{off}}\right)$ densities are indicated. The three characteristic time-scale constants are ${\tau }_1$, ${\tau }_2$, and ${\tau }_3$.

Figure 2

Photographs of the Rb and Cs cells with lockable stems.

Figure 3

Diagram of the experimental setup used in LIAD measurements. Desorption light in the visible spectrum is generated by an ${\mathrm{Ar}}^{+}$ laser at $514\mathrm{nm}$ [case (a)], while in the uv range mercury or tungsten discharge lamps are used [case (b)], respectively. A half wave plate $(\lambda ∕2)$ and a polarizing beam splitter (PBS) form a variable attenuator for the probe light. Interference filters IF1 are used to select the desired desorption wavelength, while IF2 filters are centered at the alkali-metal atomic resonance lines and are used to reject the scattered light from the desorption sources. A vibrating mirror (VM) is used to average the speckle from the ${\mathrm{Ar}}^{+}$ laser. A reflector (R) increases the average desorption intensity falling on the surface of the paraffin cell.

Figure 4

Change of the Rb vapor density in the volume of the lockable-stem cell with the stem alternately open and closed. Higher densities correspond to the open configuration. The difference in the closed-stem equilibrium densities is probably due to a variation of how tightly the stem is closed with different orientation of the glass bullet.

Figure 5

(Color online) Change of the atomic density with LIAD effect in two configuration: open and closed stem in a Cs paraffin-coated locking-stem cell. The solid line represents a fit to the data. The applied desorbing light intensity was $28\mathrm{mW}∕{\mathrm{cm}}^2$ in both cases. The desorbing light was turned on (around $t=15\mathrm{s}$) and is never turned off for these measurements.

Figure 6

(Color online) Density change with LIAD in the Rb paraffin-coated lockable-stem cell. Two cases are shown: open stem and closed stem configurations. The solid lines represent the fits to the data. The applied desorbing light is with intensity of $50\mathrm{mW}∕{\mathrm{cm}}^2$ in both cases. The desorbing light was turned on (around $60\mathrm{s}$) and then turned off (around $360\mathrm{s}$).

Figure 7

(Color online) Atomic-density dynamics in a paraffin coated ${}^{85}\mathrm{Rb}$ cell with lockable stem in the case of (a) $365\text{−}\mathrm{nm}$ desorbing light with intensity of $5\mathrm{mW}∕{\mathrm{cm}}^2$ and (b) $313\mathrm{nm}$ at $0.25\mathrm{mW}∕{\mathrm{cm}}^2$. The abrupt kinks in the plots correspond to the opening and closing of the desorbing light. Note the differences in the initial densities.

Figure 8

(Color online) Atomic density dynamics in the paraffin-coated K cell with lockable stem in case of $365\text{−}\mathrm{nm}$ desorbing light with intensity of $8\mathrm{mW}∕{\mathrm{cm}}^2$. The horizontal offset of the peaks is due to the difference in the time when the desorbing light was applied.

Figure 9

Demonstration of switching of Cs atomic density using LIAD with a lockable-stem cell (stem closed). The intensity of the desorbing $405\text{−}\mathrm{nm}$ light $(\mathrm{FWHM}=15\mathrm{nm})$ is shown on the lower trace.

Figure 10

Demonstration of Cs atomic density stabilization using LIAD with lockable-stem cell (stem closed). The intensity of the desorbing $405\text{−}\mathrm{nm}$ light $(\mathrm{FWHM}=15\mathrm{nm})$ is shown on the lower trace.

Figure 11

Normalized maximum LIAD yield in Rb lockable stem cell (stem closed) as a function of desorbing light wavelength—$514\mathrm{nm}$ (Ar laser), $365\mathrm{nm}$ (filter $\mathrm{FWHM}=60\mathrm{nm}$), and $313\mathrm{nm}$ (filter $\mathrm{FWHM}=25\mathrm{nm}$).