Physical Review A

Electron-spin-reversal phenomenon in optically pumped rubidium

Eric B. Norrgard, D. Tupa, Joan Dreiling, T. J. Gay

Published Sep 10, 2010• 7 citations

Abstract

We have studied the optical pumping of mixtures of Rb vapor and ${\mathrm{N}}_{2}$ buffer gas by laser light tuned to the ${D}_{1}$ transition having a spectral width of $~500$ MHz. The Rb densities are of the order of ${10}^{13}$ cm${}^{\ensuremath{-}3}$, while the buffer-gas pressures range from 0.1 to 10 torr. As the frequency of the right-hand circularly polarized laser is varied across the ${D}_{1}$ absorption profile, the electron spin polarization of the Rb is found to take on negative values for small negative values of pump detuning from the absorption profile center. This occurs for ${\mathrm{N}}_{2}$ pressures below $~1$ torr; at 10 torr the electron spins consistently point in the same direction as the angular momentum of the pump light. The spin-reversal effect can be understood in terms of populations of the $F=2$ ($^{85}\mathrm{Rb}$) and $F=1$ ($^{87}\mathrm{Rb}$) states caused by small unpolarized fractions in the pump beam and its elimination in terms of pressure broadening caused by the ${\mathrm{N}}_{2}$ buffer gas. We speculate that this effect could be used for fast Rb spin modulation.

DOI: 10.1103/physreva.82.033408

Related papers

Radiation trapping in rubidium optical pumping at low buffer-gas pressures

Mark Rosenberry, J. Paxon Reyes, D. Tupa +1 more

Physical Review AFeb 1, 200767 citations

Optical pumping of Rb in the presence of high-pressure He3 buffer gas

B. Larson, O. Häusser, P. P. J. Delheij +2 more

Physical Review ASep 1, 199180 citations

Spin polarization of 87Rb atoms with Xe gas and high-pressure buffer gas in a cubic cell

Hoon Yu, Jai Seung Yoo

AIP AdvancesMar 1, 20190 citations

Circular dichroism of RbHe and RbN 2 molecules

Brian Lancor, Earl Babcock, Robert Wyllie +1 more

arXiv:1007.5486Physical Review AOct 27, 201024 citations

Spin Relaxation of Optically Aligned Rubidium Vapor

W. Franzen

Physical ReviewAug 15, 1959279 citations

COLLISION-INDUCED MIXING IN THE 52P3/2 STATE OF RUBIDIUM AND THE 62P3//o STATE OF CESIUM

Joseph Yellin

Oct 4, 19660 citations

Physical Review A

Electron-spin-reversal phenomenon in optically pumped rubidium

Eric B. Norrgard, D. Tupa, Joan Dreiling, T. J. Gay

Published Sep 10, 2010• 7 citations

Publisher

Abstract

We have studied the optical pumping of mixtures of Rb vapor and

{\mathrm{N}}_{2}

buffer gas by laser light tuned to the

{D}_{1}

transition having a spectral width of

~500

MHz. The Rb densities are of the order of

{10}^{13}

{}^{\ensuremath{-}3}

, while the buffer-gas pressures range from 0.1 to 10 torr. As the frequency of the right-hand circularly polarized laser is varied across the

{D}_{1}

absorption profile, the electron spin polarization of the Rb is found to take on negative values for small negative values of pump detuning from the absorption profile center. This occurs for

{\mathrm{N}}_{2}

pressures below

~1

torr; at 10 torr the electron spins consistently point in the same direction as the angular momentum of the pump light. The spin-reversal effect can be understood in terms of populations of the

F=2

(

^{85}\mathrm{Rb}

) and

F=1

(

^{87}\mathrm{Rb}

) states caused by small unpolarized fractions in the pump beam and its elimination in terms of pressure broadening caused by the

{\mathrm{N}}_{2}

buffer gas. We speculate that this effect could be used for fast Rb spin modulation.

DOI: 10.1103/physreva.82.033408

Related papers

Radiation trapping in rubidium optical pumping at low buffer-gas pressures

Mark Rosenberry, J. Paxon Reyes, D. Tupa +1 more

We have made a systematic study of rubidium optical pumping in a simple cylindrical cell geometry with a high-power $10\phantom{\rule{0.3em}{0ex}}\mathrm{W}$ diode laser array, low magnetic fields, and buffer-gas pressures of less than $50\phantom{\rule{0.3em}{0ex}}\text{torr}$ . We have determined rubidium polarizations experimentally for ${\mathrm{H}}_{2}$ , ${\mathrm{N}}_{2}$ , He, and Ar buffer gases, with Rb number densities from ${10}^{12}\phantom{\rule{0.3em}{0ex}}\text{to}\phantom{\rule{0.3em}{0ex}}{10}^{13}\phantom{\rule{0.3em}{0ex}}{\mathrm{cm}}^{\ensuremath{-}3}$. Comparison to a relatively simple optical pumping model allows us to extract useful information about radiation trapping and quenching effects.We have made a systematic study of rubidium optical pumping in a simple cylindrical cell geometry with a high-power $10\phantom{\rule{0.3em}{0ex}}\mathrm{W}$ diode laser array, low magnetic fields, and buffer-gas pressures of less than $50\phantom{\rule{0.3em}{0ex}}\text{torr}$. We have determined rubidium polarizations experimentally for ${\mathrm{H}}_{2}$, ${\mathrm{N}}_{2}$, He, and Ar buffer gases, with Rb number densities from ${10}^{12}\phantom{\rule{0.3em}{0ex}}\text{to}\phantom{\rule{0.3em}{0ex}}{10}^{13}\phantom{\rule{0.3em}{0ex}}{\mathrm{cm}}^{\ensuremath{-}3}$. Comparison to a relatively simple optical pumping model allows us to extract useful information about radiation trapping and quenching effects.

Physical Review AFeb 1, 200767 citations

Optical pumping of Rb in the presence of high-pressure He3 buffer gas

B. Larson, O. Häusser, P. P. J. Delheij +2 more

A cryogenic technique has been used to produce polarized $^{3}\mathrm{He}$ targets of up to relative density p=12 atm (\ensuremath{\approxeq}3\ifmmode\times\else\texttimes\fi{} ${10}^{20}$ $^{3}\mathrm{He}$ atoms/ ${\mathrm{cm}}^{3}$ ; p=1 atm corresponds to 760 Torr or 101.3 kPa pressure at 273 K). In these targets $^{3}\mathrm{He}$ nuclei are polarized by spin-exchange collisions with optically pumped rubidium atoms. From transmission measurements at wavelengths of 790--800 nm, we have determined pressure shifts, linewidths, and line-shape asymmetries for the Rb 5 ${\mathit{S}}_{1/2}$ \ensuremath{\rightarrow}5 ${\mathit{P}}_{1/2}$ D1 transition. The Rb spin-destruction rate was found to exhibit a quadratic increase versus $^{3}\mathrm{He}$ pressure, which indicates the importance of Rb${\mathrm{\ensuremath{-}}}^{3}$He${\mathrm{\ensuremath{-}}}^{3}$He collision processes. The transmission results for circularly polarized light are well described by a model that predicts the dependence of the average Rb polarization on Rb density, $^{3}\mathrm{He}$ pressure, light intensity, and cell geometry. The Rb${\mathrm{\ensuremath{-}}}^{3}$He spin-exchange cross section, 〈${\mathrm{\ensuremath{\sigma}}}_{\mathrm{SE}}$v〉=6.1\ifmmode\times\else\texttimes\fi{}${10}^{\mathrm{\ensuremath{-}}20}$ ${\mathrm{cm}}^{3}$ ${\mathrm{s}}^{\mathrm{\ensuremath{-}}1}$, was found to be independent of $^{3}\mathrm{He}$ pressure up to p=12.1 atm. Maximum $^{3}\mathrm{He}$ polarizations of 72--79% were observed with cells of 17 ${\mathrm{cm}}^{3}$ volume that contained $^{3}\mathrm{He}$ at p=6--9 atm.A cryogenic technique has been used to produce polarized $^{3}\mathrm{He}$ targets of up to relative density p=12 atm (\ensuremath{\approxeq}3\ifmmode\times\else\texttimes\fi{}${10}^{20}$ $^{3}\mathrm{He}$ atoms/${\mathrm{cm}}^{3}$; p=1 atm corresponds to 760 Torr or 101.3 kPa pressure at 273 K). In these targets $^{3}\mathrm{He}$ nuclei are polarized by spin-exchange collisions with optically pumped rubidium atoms. From transmission measurements at wavelengths of 790--800 nm, we have determined pressure shifts, linewidths, and line-shape asymmetries for the Rb 5${\mathit{S}}_{1/2}$\ensuremath{\rightarrow}5${\mathit{P}}_{1/2}$ D1 transition. The Rb spin-destruction rate was found to exhibit a quadratic increase versus $^{3}\mathrm{He}$ pressure, which indicates the importance of Rb${\mathrm{\ensuremath{-}}}^{3}$He${\mathrm{\ensuremath{-}}}^{3}$He collision processes. The transmission results for circularly polarized light are well described by a model that predicts the dependence of the average Rb polarization on Rb density, $^{3}\mathrm{He}$ pressure, light intensity, and cell geometry. The Rb${\mathrm{\ensuremath{-}}}^{3}$He spin-exchange cross section, 〈${\mathrm{\ensuremath{\sigma}}}_{\mathrm{SE}}$v〉=6.1\ifmmode\times\else\texttimes\fi{}${10}^{\mathrm{\ensuremath{-}}20}$ ${\mathrm{cm}}^{3}$ ${\mathrm{s}}^{\mathrm{\ensuremath{-}}1}$, was found to be independent of $^{3}\mathrm{He}$ pressure up to p=12.1 atm. Maximum $^{3}\mathrm{He}$ polarizations of 72--79% were observed with cells of 17 ${\mathrm{cm}}^{3}$ volume that contained $^{3}\mathrm{He}$ at p=6--9 atm.

Physical Review ASep 1, 199180 citations

Spin polarization of 87Rb atoms with Xe gas and high-pressure buffer gas in a cubic cell

Hoon Yu, Jai Seung Yoo

We simulated the optical pumping rate of 87Rb atoms with Xe and high-pressure buffer gas in a cubic cell. We calculated absorption cross-section as a function of pumping laser frequency by considering a pressure and Doppler broadening as gas temperature varies from 364 K to 414 K. In a steady state the spin polarization and the atomic population of 87Rb atoms were obtained by optical pumping in each ground state. We calculated the optimum beam waist, linewidth and detuning of pumping beam to achieve higher population of polarized atoms at cell parameters such as temperature, size. We simulated that the optimum beam waist is 0.3 times of cubic cell length at 250 Torr of di-nitrogen and 50 Torr of Xe gas pressure. The optimum laser beam linewidth parabolically increases with increasing the temperature in range of few ten kelvin and it exponentially decrease with increasing the cubic cell length. We also observed that few ten GHz detuned laser frequency increases the optical pumping rate. These numerical results show appropriate experimental parameter as a function of cell temperature and size to get maximum population of spin polarized atoms in given temperature range.We simulated the optical pumping rate of 87Rb atoms with Xe and high-pressure buffer gas in a cubic cell. We calculated absorption cross-section as a function of pumping laser frequency by considering a pressure and Doppler broadening as gas temperature varies from 364 K to 414 K. In a steady state the spin polarization and the atomic population of 87Rb atoms were obtained by optical pumping in each ground state. We calculated the optimum beam waist, linewidth and detuning of pumping beam to achieve higher population of polarized atoms at cell parameters such as temperature, size. We simulated that the optimum beam waist is 0.3 times of cubic cell length at 250 Torr of di-nitrogen and 50 Torr of Xe gas pressure. The optimum laser beam linewidth parabolically increases with increasing the temperature in range of few ten kelvin and it exponentially decrease with increasing the cubic cell length. We also observed that few ten GHz detuned laser frequency increases the optical pumping rate. These numerical results show appropriate experimental parameter as a function of cell temperature and size to get maximum population of spin polarized atoms in given temperature range.

AIP AdvancesMar 1, 20190 citations

Circular dichroism of RbHe and RbN 2 molecules

Brian Lancor, Earl Babcock, Robert Wyllie +1 more

We present measurements of the circular dichroism of optically pumped Rb vapor near the ${D}_{1}$ resonance line. Collisions with the buffer gases $^{3}\mathrm{He}$ and ${\mathrm{N}}_{2}$ reduce the transparency of the vapor, even when fully polarized. We use two methods to measure this effect, show that the He results can be understood from RbHe potential curves, and show how this effect conspires with the spectral profile of the optical pumping light to increase the laser power demands for optical pumping of very optically thick samples.We present measurements of the circular dichroism of optically pumped Rb vapor near the ${D}_{1}$ resonance line. Collisions with the buffer gases $^{3}\mathrm{He}$ and ${\mathrm{N}}_{2}$ reduce the transparency of the vapor, even when fully polarized. We use two methods to measure this effect, show that the He results can be understood from RbHe potential curves, and show how this effect conspires with the spectral profile of the optical pumping light to increase the laser power demands for optical pumping of very optically thick samples.

arXiv:1007.5486Physical Review AOct 27, 201024 citations

Spin Relaxation of Optically Aligned Rubidium Vapor

W. Franzen

A new optical method for studying the spin relaxation of optically aligned rubidium vapor is described. In this method, the pumping radiation, consisting of circularly polarized ${D}_{1}$ resonance radiation, is suddenly shut off and then turned on again after a known time interval. The relaxation which takes place during the interval of darkness causes the vapor to become more opaque to the pumping radiation at a rate which is determined by the relaxation time. A large degree of alignment, as well as a relaxation time of about 80 milliseconds, were observed in a closed-off evacuated cylindrical glass cell completely lined, except for $\frac{1}{200}$ of the wall area, with a thin film of tetracontane ( ${\mathrm{C}}_{40}$ ${\mathrm{H}}_{82}$ ). The variation of relaxation time with buffer gas pressure was studied in this cell and in an unlined glass cell. From the observations with the unlined cell, diffusion coefficients for rubidium in neon and argon of 0.31 ${\mathrm{cm}}^{2}$ /sec and 0.24 ${\mathrm{cm}}^{2}$ /sec, respectively, can be deduced. Observed cross sections for disorientation collisions between aligned ground-state rubidium atoms and neon, argon, krypton, and xenon atoms are 5.2\ifmmode\times\else\texttimes\fi{}${10}^{\ensuremath{-}23}$ ${\mathrm{cm}}^{2}$ , 3.7\ifmmode\times\else\texttimes\fi{}${10}^{\ensuremath{-}22}$ ${\mathrm{cm}}^{2}$ , 5.9\ifmmode\times\else\texttimes\fi{}${10}^{\ensuremath{-}21}$ ${\mathrm{cm}}^{2}$ , and 1.3\ifmmode\times\else\texttimes\fi{}${10}^{\ensuremath{-}20}$ ${\mathrm{cm}}^{2}$ , respectively. In the evacuated tetracontane-lined cell, the relaxation time decreased by 30% for a tenfold increase in rubidium vapor pressure. An explanation for this relatively weak dependence is suggested. The longest observed relaxation time was approximately 0.4 seconds in a tetracontanelined cell filled with neon to a pressure of 3 cm Hg.A new optical method for studying the spin relaxation of optically aligned rubidium vapor is described. In this method, the pumping radiation, consisting of circularly polarized ${D}_{1}$ resonance radiation, is suddenly shut off and then turned on again after a known time interval. The relaxation which takes place during the interval of darkness causes the vapor to become more opaque to the pumping radiation at a rate which is determined by the relaxation time. A large degree of alignment, as well as a relaxation time of about 80 milliseconds, were observed in a closed-off evacuated cylindrical glass cell completely lined, except for $\frac{1}{200}$ of the wall area, with a thin film of tetracontane (${\mathrm{C}}_{40}$${\mathrm{H}}_{82}$). The variation of relaxation time with buffer gas pressure was studied in this cell and in an unlined glass cell. From the observations with the unlined cell, diffusion coefficients for rubidium in neon and argon of 0.31 ${\mathrm{cm}}^{2}$/sec and 0.24 ${\mathrm{cm}}^{2}$/sec, respectively, can be deduced. Observed cross sections for disorientation collisions between aligned ground-state rubidium atoms and neon, argon, krypton, and xenon atoms are 5.2\ifmmode\times\else\texttimes\fi{}${10}^{\ensuremath{-}23}$ ${\mathrm{cm}}^{2}$, 3.7\ifmmode\times\else\texttimes\fi{}${10}^{\ensuremath{-}22}$ ${\mathrm{cm}}^{2}$, 5.9\ifmmode\times\else\texttimes\fi{}${10}^{\ensuremath{-}21}$ ${\mathrm{cm}}^{2}$, and 1.3\ifmmode\times\else\texttimes\fi{}${10}^{\ensuremath{-}20}$ ${\mathrm{cm}}^{2}$, respectively. In the evacuated tetracontane-lined cell, the relaxation time decreased by 30% for a tenfold increase in rubidium vapor pressure. An explanation for this relatively weak dependence is suggested. The longest observed relaxation time was approximately 0.4 seconds in a tetracontanelined cell filled with neon to a pressure of 3 cm Hg.

Physical ReviewAug 15, 1959279 citations

COLLISION-INDUCED MIXING IN THE 52P3/2 STATE OF RUBIDIUM AND THE 62P3//o STATE OF CESIUM

Joseph Yellin

Alkali-metal vapors of rubidium and cesium have been optically pumped, with the D2 component of the resonance radiation and the reversal of the ground-state polarization observed as a function of buffer-gas pressure.It is well known that when complete mixing occurs in the 2p3/2 state, the polarization achieved in the grolfnd state (ZS1jz) is opposite to that obtained with the D 1 component of the resonance radiation when circularly polarized light is used.However, in the absence of mixing in the 2 P3/2 state, the sign of the polarization is the same for both D 1 and Dz light.For some finite degree of mixing of the 2p3/2 state, the equilibrium electronic polarization vanishes.From the null points observed in the Dz pumping signal vs buffer-gas -pressure curve, we have determined relative cross sections for collisional.disorientation of the 2 P3/2 state of a polarized Rb orCs atom.For Rb85 we fmd a 3 ; 2 (He) = 0.44 ± 15%, a 3 ,; (Ne) = 0.45 ± 15o/o, a 3 ; 2 (Kr) = 1.26 ± l5o/o, and a 3 ; 2 (Xe) = 1.46 ± J5o/o:; for Rb87 we find &3j 2 (He) = 0.47 ± 15o/o, a3/2(Ne) = 0.46 ± l5o/o, a3/ 2 (Kr) = 1.32 ± 15o/o, and a3/2 (Xe) = 1.46 ± 15%."For C s, a 3{ 2 (He) = Oo38 ± 15o/o, a3/2 (N e) = 0.42 ± 15 o/o, a3j2(Kr) = L22 ± 15o/o, and a 3 ;2(Xe = 1.45 ± 15o/o.All cross sections are relative to a3/2(Ar)o -• ••• -1-UCRL-17175Alkali-metal vapors of rubidium and cesium have been optically pumped, with the D2 component of the resonance radiation and the reversal of the ground-state polarization observed as a function of buffer-gas pressure.It is well known that when complete mixing occurs in the 2p3/2 state, the polarization achieved in the grolfnd state (ZS1jz) is opposite to that obtained with the D 1 component of the resonance radiation when circularly polarized light is used.However, in the absence of mixing in the 2 P3/2 state, the sign of the polarization is the same for both D 1 and Dz light.For some finite degree of mixing of the 2p3/2 state, the equilibrium electronic polarization vanishes.From the null points observed in the Dz pumping signal vs buffer-gas -pressure curve, we have determined relative cross sections for collisional.disorientation of the 2 P3/2 state of a polarized Rb orCs atom.For Rb85 we fmd a 3 ; 2 (He) = 0.44 ± 15%, a 3 ,; (Ne) = 0.45 ± 15o/o, a 3 ; 2 (Kr) = 1.26 ± l5o/o, and a 3 ; 2 (Xe) = 1.46 ± J5o/o:; for Rb87 we find &3j 2 (He) = 0.47 ± 15o/o, a3/2(Ne) = 0.46 ± l5o/o, a3/ 2 (Kr) = 1.32 ± 15o/o, and a3/2 (Xe) = 1.46 ± 15%."For C s, a 3{ 2 (He) = Oo38 ± 15o/o, a3/2 (N e) = 0.42 ± 15 o/o, a3j2(Kr) = L22 ± 15o/o, and a 3 ;2(Xe = 1.45 ± 15o/o.All cross sections are relative to a3/2(Ar)o -• ••• -1-UCRL-17175

Oct 4, 19660 citations

We have studied the optical pumping of mixtures of Rb vapor and

{\mathrm{N}}_{2}

buffer gas by laser light tuned to the

{D}_{1}

transition having a spectral width of

~500

MHz. The Rb densities are of the order of

{10}^{13}

{}^{\ensuremath{-}3}

, while the buffer-gas pressures range from 0.1 to 10 torr. As the frequency of the right-hand circularly polarized laser is varied across the

{D}_{1}

absorption profile, the electron spin polarization of the Rb is found to take on negative values for small negative values of pump detuning from the absorption profile center. This occurs for

{\mathrm{N}}_{2}

pressures below

~1

torr; at 10 torr the electron spins consistently point in the same direction as the angular momentum of the pump light. The spin-reversal effect can be understood in terms of populations of the

F=2

(

^{85}\mathrm{Rb}

) and

F=1

(

^{87}\mathrm{Rb}

) states caused by small unpolarized fractions in the pump beam and its elimination in terms of pressure broadening caused by the

{\mathrm{N}}_{2}

buffer gas. We speculate that this effect could be used for fast Rb spin modulation.

We have made a systematic study of rubidium optical pumping in a simple cylindrical cell geometry with a high-power

10\phantom{\rule{0.3em}{0ex}}\mathrm{W}

diode laser array, low magnetic fields, and buffer-gas pressures of less than

50\phantom{\rule{0.3em}{0ex}}\text{torr}

. We have determined rubidium polarizations experimentally for

{\mathrm{H}}_{2}

{\mathrm{N}}_{2}

, He, and Ar buffer gases, with Rb number densities from ${10}^{12}\phantom{\rule{0.3em}{0ex}}\text{to}\phantom{\rule{0.3em}{0ex}}{10}^{13}\phantom{\rule{0.3em}{0ex}}{\mathrm{cm}}^{\ensuremath{-}3}$. Comparison to a relatively simple optical pumping model allows us to extract useful information about radiation trapping and quenching effects.

A cryogenic technique has been used to produce polarized

^{3}\mathrm{He}

targets of up to relative density p=12 atm (\ensuremath{\approxeq}3\ifmmode\times\else\texttimes\fi{}

{10}^{20}

^{3}\mathrm{He}

atoms/

{\mathrm{cm}}^{3}

; p=1 atm corresponds to 760 Torr or 101.3 kPa pressure at 273 K). In these targets

^{3}\mathrm{He}

nuclei are polarized by spin-exchange collisions with optically pumped rubidium atoms. From transmission measurements at wavelengths of 790--800 nm, we have determined pressure shifts, linewidths, and line-shape asymmetries for the Rb 5

{\mathit{S}}_{1/2}

\ensuremath{\rightarrow}5

{\mathit{P}}_{1/2}

D1 transition. The Rb spin-destruction rate was found to exhibit a quadratic increase versus

^{3}\mathrm{He}

pressure, which indicates the importance of Rb${\mathrm{\ensuremath{-}}}^{3}$He${\mathrm{\ensuremath{-}}}^{3}$He collision processes. The transmission results for circularly polarized light are well described by a model that predicts the dependence of the average Rb polarization on Rb density,

^{3}\mathrm{He}

pressure, light intensity, and cell geometry. The Rb${\mathrm{\ensuremath{-}}}^{3}$He spin-exchange cross section, 〈${\mathrm{\ensuremath{\sigma}}}_{\mathrm{SE}}$v〉=6.1\ifmmode\times\else\texttimes\fi{}${10}^{\mathrm{\ensuremath{-}}20}$

{\mathrm{cm}}^{3}

${\mathrm{s}}^{\mathrm{\ensuremath{-}}1}$, was found to be independent of

^{3}\mathrm{He}

pressure up to p=12.1 atm. Maximum

^{3}\mathrm{He}

polarizations of 72--79% were observed with cells of 17

{\mathrm{cm}}^{3}

volume that contained

^{3}\mathrm{He}

at p=6--9 atm.

We present measurements of the circular dichroism of optically pumped Rb vapor near the

{D}_{1}

resonance line. Collisions with the buffer gases

^{3}\mathrm{He}

and

{\mathrm{N}}_{2}

reduce the transparency of the vapor, even when fully polarized. We use two methods to measure this effect, show that the He results can be understood from RbHe potential curves, and show how this effect conspires with the spectral profile of the optical pumping light to increase the laser power demands for optical pumping of very optically thick samples.

A new optical method for studying the spin relaxation of optically aligned rubidium vapor is described. In this method, the pumping radiation, consisting of circularly polarized

{D}_{1}

resonance radiation, is suddenly shut off and then turned on again after a known time interval. The relaxation which takes place during the interval of darkness causes the vapor to become more opaque to the pumping radiation at a rate which is determined by the relaxation time. A large degree of alignment, as well as a relaxation time of about 80 milliseconds, were observed in a closed-off evacuated cylindrical glass cell completely lined, except for

\frac{1}{200}

of the wall area, with a thin film of tetracontane (

{\mathrm{C}}_{40}

{\mathrm{H}}_{82}

). The variation of relaxation time with buffer gas pressure was studied in this cell and in an unlined glass cell. From the observations with the unlined cell, diffusion coefficients for rubidium in neon and argon of 0.31

{\mathrm{cm}}^{2}

/sec and 0.24

{\mathrm{cm}}^{2}

/sec, respectively, can be deduced. Observed cross sections for disorientation collisions between aligned ground-state rubidium atoms and neon, argon, krypton, and xenon atoms are 5.2\ifmmode\times\else\texttimes\fi{}${10}^{\ensuremath{-}23}$

{\mathrm{cm}}^{2}

, 3.7\ifmmode\times\else\texttimes\fi{}${10}^{\ensuremath{-}22}$

{\mathrm{cm}}^{2}

, 5.9\ifmmode\times\else\texttimes\fi{}${10}^{\ensuremath{-}21}$

{\mathrm{cm}}^{2}

, and 1.3\ifmmode\times\else\texttimes\fi{}${10}^{\ensuremath{-}20}$

{\mathrm{cm}}^{2}

, respectively. In the evacuated tetracontane-lined cell, the relaxation time decreased by 30% for a tenfold increase in rubidium vapor pressure. An explanation for this relatively weak dependence is suggested. The longest observed relaxation time was approximately 0.4 seconds in a tetracontanelined cell filled with neon to a pressure of 3 cm Hg.