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arXiv:2108.04487 · Physical Review A

Measurement of the temperature dependence of dwell time and spin relaxation probability of Rb atoms on paraffin surfaces using a beam-scattering method

Kanta Asakawa, Yutaro Tanaka, Kenta Uemura, Norihiro Matsuzaka, Kunihiro Nishikawa, Yuki Oguma, Hiroaki Usui, A. Hatakeyama

Published Dec 6, 2021• 9 citations
arXivHTMLPDF

Abstract

The scattering of Rb atoms on an antirelaxation coating was studied. No significant change in the spin relaxation probability of Rb atoms by single scattering from a tetracontane surface was observed by cooling the film from 305 to 123 K. The mean surface dwell time was estimated using a time-resolved method. Delay-time spectra, from which mean surface dwell times can be estimated, were measured at 305, 153, and 123 K, with a time window of $9.3\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}5}$ s. The increase in mean surface dwell time with cooling from 305 to 123 K was smaller than $4.4\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}6}$ s, which is significantly smaller than the value expected from the mean dwell time at room temperature measured using the Larmor frequency shift. These results can be explained by assuming a small number of scattering components, with a mean surface dwell time at least three orders of magnitude longer than the majority component.

DOI
10.1103/physreva.104.063106

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Dwell time and spin relaxation probability of Rb atoms on anti-spin-relaxation coatings

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The scattering of Rb atoms on paraffin coatings was studied. The results showed that the increase of surface dwell time by cooling from 305 to 123 K is smaller than 2.3 × 10−6 s.

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Measurement of dwell times of spin polarized rubidium atoms on octadecyltrichlorosilane- and paraffin-coated surfaces

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We report the measurement of dwell times of spin polarized Rb atoms on octadecyltrichlorosilane (OTS)- and paraffin-coated surfaces. We find that at a cell temperature of 72 °C the dwell times for OTS- and paraffin-coated surfaces are 0.9±0.1 μs and 1.8±0.2 μs, respectively. Since the relaxation probability on paraffin is almost one order of magnitude smaller than that on OTS, the longer dwell time for paraffin indicates that the average strength of the interactions experienced by Rb atoms while they are inside paraffin is much weaker than while they are inside OTS.

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Methods commonly used in surface science have difficulties in studying surface interaction between spin polarized atoms and anti-relaxation coatings in sealed atomic vapour cells. The average dwell time of atom-wall collisions can provide important information for understanding the atom surface interaction. Here we present a simple method for directly measuring the average dwell time of spin polarized rubidium atoms on coated glass surfaces. The method relies on evanescent-wave induced light shift of the Zeeman resonance of Rb atomic spins, and does not depend on the microscopic details of surface interactions. This is the only reliable method currently available for measuring surface dwell time of spin polarized atoms sealed in vapor cells.

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The study of wall interactions of spin polarized rubidium atoms using the frequency shift in the electron paramagnetic resonance of the rubidium atoms

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I studied the effect of wall collisions on the electron paramagnetic resonance (EPR) of gas phase alkali metal atoms (87Rb). Two types of walls were studied: antirelaxation-coated walls and RbH-coated walls. I measured the dwell times of spin polarized Rb atoms on the two most common antirelaxation coatings, octadecyltrichlorosilane (OTS)- and paraffin. I found that at a cell temperature of 72 C the dwell times for OTS- and paraffin-coated walls are 0.9 ± 0.1 μs and 1.8 ± 0.2 μs, respectively. The implication of these dwell times, which are much longer than what was previously reported in the literature, is discussed in connection with the relaxing property of these coatings. In cells coated with RbH salt I made the first observation of the EPR frequency shift of the gas phase 87Rb atoms. Due to collisions with the RbH salt, which was nuclear spin polarized by spin exchange with optically pumped Rb vapor. The measured EPR frequency shifts are of the order of several hundred Hz in a millimeter-sized cell. By measuring the dependence of the EPR frequency shifts on cell length and by comparing the EPR frequency shifts in RbH-coated cells with those in OTS-coated cells, I provided convincing evidence that the observed EPR frequency shifts are due to collisions with RbH-coated walls, and not due to gas phase processes. The EPR frequency shift is due to the Fermi contact interaction between the s-electron of the adsorbed 87Rb atom and the polarized nucleus on the salt surface. The measured EPR frequency shifts allowed me to calculate the ensemble-averaged phase shift experienced by the Rb atom while adsorbed on the walls. Under our experimental condition this is about 70 mrad. My experiment opens up the possibility of studying surface NMR using gas phase EPR. The phase shift is proportional to the surface nuclear polarization, thus provides an interesting method for measuring the surface nuclear polarization using gas phase EPR. My observation will alert the high precision miniature atomic magnetometry community that collisions with cell walls may cause a systematic error and line broadening in the magnetic resonance frequency.

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We present a simple method for directly measuring the average dwell time of spin-polarized Rb atoms on coated Pyrex glass surfaces. The method relies on the light shift of the Zeeman resonances of spin-polarized Rb atoms pumped and probed by evanescent waves, and does not depend on the microscopic details of surface interactions. We use a cell whose length is adjustable between 70 and $500\text{ }\text{ }\ensuremath{\mu}\mathrm{m}$. The inverse of the difference between the frequency shifts caused by ${\ensuremath{\sigma}}^{+}$ and ${\ensuremath{\sigma}}^{\ensuremath{-}}$ pump beams depends linearly on the cell length, from which we obtain the average dwell time ${\ensuremath{\tau}}_{s}$. For a Pyrex glass cell coated with octadecyltrichlorosilane we find that ${\ensuremath{\tau}}_{s}=0.53\ifmmode\pm\else\textpm\fi{}0.03\text{ }\text{ }\ensuremath{\mu}\mathrm{s}$ at a cell wall temperature of $103\text{ }\ifmmode^\circ\else\textdegree\fi{}\mathrm{C}$. The temperature dependence of ${\ensuremath{\tau}}_{s}$ is fitted to ${\ensuremath{\tau}}_{s}={\overline{\ensuremath{\tau}}}_{0}\mathrm{exp}({E}_{a}/kT)$, yielding a preexponential factor ${\overline{\ensuremath{\tau}}}_{0}={2.2}_{\ensuremath{-}1.4}^{+5.1}\text{ }\text{ }\mathrm{ns}$ and an activation energy ${E}_{a}=0.19\ifmmode\pm\else\textpm\fi{}0.03\text{ }\text{ }\mathrm{eV}$.

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Thermalization of rubidium atoms scattered from a low-temperature paraffin film

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Abstract With an objective to explore the surface interaction between alkali-metal atoms and an inert organic coating, we used an atomic beam to measure the velocity distribution of gaseous rubidium atoms scattered from a low-temperature tetracontane film. When the film temperature decreased from 300 K to 200 K, the number of scattered atoms did not change. At below 200 K, the number began to decrease until, finally, no scattered atoms were observable at 140 K. X-ray photoelectron spectroscopy at 160 K or below revealed rubidium atoms on the film surface. The temperature of the scattered atoms was the same as that of the film. Thermalization of scattered atoms at room temperature was reported previously, but this study is the first to report thermalization at low temperatures.

Journal of Physics B Atomic Molecular and Optical Physics•Feb 9, 2026•0 citations
The scattering of Rb atoms on an antirelaxation coating was studied. No significant change in the spin relaxation probability of Rb atoms by single scattering from a tetracontane surface was observed by cooling the film from 305 to 123 K. The mean surface dwell time was estimated using a time-resolved method. Delay-time spectra, from which mean surface dwell times can be estimated, were measured at 305, 153, and 123 K, with a time window of 9.3\ifmmode×\else\texttimes\fi10\ensuremath−59.3\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}5}9.3\ifmmode×\else\texttimes\fi10\ensuremath−5 s. The increase in mean surface dwell time with cooling from 305 to 123 K was smaller than 4.4\ifmmode×\else\texttimes\fi10\ensuremath−64.4\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}6}4.4\ifmmode×\else\texttimes\fi10\ensuremath−6 s, which is significantly smaller than the value expected from the mean dwell time at room temperature measured using the Larmor frequency shift. These results can be explained by assuming a small number of scattering components, with a mean surface dwell time at least three orders of magnitude longer than the majority component.
We report the measurement of dwell times of spin polarized Rb atoms on octadecyltrichlorosilane (OTS)- and paraffin-coated surfaces. We find that at a cell temperature of 72 °C the dwell times for OTS- and paraffin-coated surfaces are 0.9±0.1 μs and 1.8±0.2 μs, respectively. Since the relaxation probability on paraffin is almost one order of magnitude smaller than that on OTS, the longer dwell time for paraffin indicates that the average strength of the interactions experienced by Rb atoms while they are inside paraffin is much weaker than while they are inside OTS.
Methods commonly used in surface science have difficulties in studying surface interaction between spin polarized atoms and anti-relaxation coatings in sealed atomic vapour cells. The average dwell time of atom-wall collisions can provide important information for understanding the atom surface interaction. Here we present a simple method for directly measuring the average dwell time of spin polarized rubidium atoms on coated glass surfaces. The method relies on evanescent-wave induced light shift of the Zeeman resonance of Rb atomic spins, and does not depend on the microscopic details of surface interactions. This is the only reliable method currently available for measuring surface dwell time of spin polarized atoms sealed in vapor cells.
I studied the effect of wall collisions on the electron paramagnetic resonance (EPR) of gas phase alkali metal atoms (87Rb). Two types of walls were studied: antirelaxation-coated walls and RbH-coated walls. I measured the dwell times of spin polarized Rb atoms on the two most common antirelaxation coatings, octadecyltrichlorosilane (OTS)- and paraffin. I found that at a cell temperature of 72 C the dwell times for OTS- and paraffin-coated walls are 0.9 ± 0.1 μs and 1.8 ± 0.2 μs, respectively. The implication of these dwell times, which are much longer than what was previously reported in the literature, is discussed in connection with the relaxing property of these coatings. In cells coated with RbH salt I made the first observation of the EPR frequency shift of the gas phase 87Rb atoms. Due to collisions with the RbH salt, which was nuclear spin polarized by spin exchange with optically pumped Rb vapor. The measured EPR frequency shifts are of the order of several hundred Hz in a millimeter-sized cell. By measuring the dependence of the EPR frequency shifts on cell length and by comparing the EPR frequency shifts in RbH-coated cells with those in OTS-coated cells, I provided convincing evidence that the observed EPR frequency shifts are due to collisions with RbH-coated walls, and not due to gas phase processes. The EPR frequency shift is due to the Fermi contact interaction between the s-electron of the adsorbed 87Rb atom and the polarized nucleus on the salt surface. The measured EPR frequency shifts allowed me to calculate the ensemble-averaged phase shift experienced by the Rb atom while adsorbed on the walls. Under our experimental condition this is about 70 mrad. My experiment opens up the possibility of studying surface NMR using gas phase EPR. The phase shift is proportional to the surface nuclear polarization, thus provides an interesting method for measuring the surface nuclear polarization using gas phase EPR. My observation will alert the high precision miniature atomic magnetometry community that collisions with cell walls may cause a systematic error and line broadening in the magnetic resonance frequency.
We present a simple method for directly measuring the average dwell time of spin-polarized Rb atoms on coated Pyrex glass surfaces. The method relies on the light shift of the Zeeman resonances of spin-polarized Rb atoms pumped and probed by evanescent waves, and does not depend on the microscopic details of surface interactions. We use a cell whose length is adjustable between 70 and $500\text{ }\text{ }\ensuremath{\mu}\mathrm{m}$. The inverse of the difference between the frequency shifts caused by ${\ensuremath{\sigma}}^{+}$ and ${\ensuremath{\sigma}}^{\ensuremath{-}}$ pump beams depends linearly on the cell length, from which we obtain the average dwell time ${\ensuremath{\tau}}_{s}$. For a Pyrex glass cell coated with octadecyltrichlorosilane we find that ${\ensuremath{\tau}}_{s}=0.53\ifmmode\pm\else\textpm\fi{}0.03\text{ }\text{ }\ensuremath{\mu}\mathrm{s}$ at a cell wall temperature of $103\text{ }\ifmmode^\circ\else\textdegree\fi{}\mathrm{C}$. The temperature dependence of ${\ensuremath{\tau}}_{s}$ is fitted to ${\ensuremath{\tau}}_{s}={\overline{\ensuremath{\tau}}}_{0}\mathrm{exp}({E}_{a}/kT)$, yielding a preexponential factor ${\overline{\ensuremath{\tau}}}_{0}={2.2}_{\ensuremath{-}1.4}^{+5.1}\text{ }\text{ }\mathrm{ns}$ and an activation energy ${E}_{a}=0.19\ifmmode\pm\else\textpm\fi{}0.03\text{ }\text{ }\mathrm{eV}$.
Abstract With an objective to explore the surface interaction between alkali-metal atoms and an inert organic coating, we used an atomic beam to measure the velocity distribution of gaseous rubidium atoms scattered from a low-temperature tetracontane film. When the film temperature decreased from 300 K to 200 K, the number of scattered atoms did not change. At below 200 K, the number began to decrease until, finally, no scattered atoms were observable at 140 K. X-ray photoelectron spectroscopy at 160 K or below revealed rubidium atoms on the film surface. The temperature of the scattered atoms was the same as that of the film. Thermalization of scattered atoms at room temperature was reported previously, but this study is the first to report thermalization at low temperatures.