Optical-pumping effects in level-crossing measurements

H. Liening

Claude N. Cohen-Tannoudji

Robert E. Slocum

Parametric resonances associated with zero-field level crossings of the ${2}^{3}{S}_{1}$ level of ${\mathrm{He}}^{4}$ have been investigated using transverse optical pumping. A steady-state technique based on the $n=0$, $p=0$ resonance (Hanle effect) is used to measure spin-state lifetimes and determine the dependence of the thermal relaxation time on the state of the active helium discharge. The $n=0$, $p=1$ resonance is quite strong and suitable for measuring weak magnetic fields. A sensitivity of 1.0 \ifmmode\times\else\texttimes\fi{} ${10}^{\ensuremath{-}8}$ G is demonstrated for this measurement technique.

T. Dohnalik, Wojciech Gawlik

Optical pumping activity in Poland is reviewed with particular emphasis on Professor Kastler's inspiration in its development. The reviewed activity concerns studies of relaxation, modulation effects, level crossing and anticrossing effects, dressed atom model and of the forward scattering of resonance radiation.

V.Paul Kaftandjian, Lewis S. Klein, Wilhelm Hanle

Richard Marrus, Joseph Yellin

Detailed studies have been made of the light transmitted through rubidium-87 vapor during the optical-pumping process, both with and without buffer gas present. The observed transients are single exponentials with no buffer gas present, and double exponentials with buffer gas present, over a wide range of pumping intensities and relaxation times. These results are in excellent agreement with the predictions based on phenomenological equations in which nuclear spin is included and a single relaxation time is assumed. From a study of the amplitudes of the two exponential components of the optical-pumping transient, an effective cross section ${\ensuremath{\sigma}}_{\mathrm{eff}}$ is deduced for the disorientation of rubidium-87 within the $5^{2}P_{\frac{1}{2}}$ state as a result of its collision with a buffer-gas atom. It is shown that ${\ensuremath{\sigma}}_{\mathrm{eff}}={\ensuremath{\sigma}}_{\frac{1}{2}}+{\ensuremath{\sigma}}_{\frac{3}{2}}$, where ${\ensuremath{\sigma}}_{\frac{1}{2}}$ is the cross section for disorientation within the $5^{2}P_{\frac{1}{2}}$ level, and ${\ensuremath{\sigma}}_{\frac{3}{2}}$ is the cross section for transfer from the $5^{2}P_{\frac{1}{2}}$ level to the $5^{2}P_{\frac{3}{2}}$ level by means of collisions with the buffer gas. On the basis of recently measured values for ${\ensuremath{\sigma}}_{\frac{3}{2}}$, values are deduced for ${\ensuremath{\sigma}}_{\frac{1}{2}}$. The cross sections are: ${\ensuremath{\sigma}}_{\frac{1}{2}}(\mathrm{R}\mathrm{b}\ensuremath{-}\mathrm{H}\mathrm{e})=1.5(0.8)\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}17}$ ${\mathrm{cm}}^{2}$, ${\ensuremath{\sigma}}_{\frac{1}{2}}(\mathrm{R}\mathrm{b}\ensuremath{-}\mathrm{N}\mathrm{e})=4.4(2.2)\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}17}$ ${\mathrm{cm}}^{2}$, and ${\ensuremath{\sigma}}_{\frac{1}{2}}(\mathrm{R}\mathrm{b}\ensuremath{-}\mathrm{A}\mathrm{r})=3.5(1.8)\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}16}$ ${\mathrm{cm}}^{2}$. These cross sections are deduced from a model in which the probabilities for ${\mathrm{Rb}}^{87}$ to relax from any hyperfine level to any other are all equal. This model gives a better fit with the observed transients than the assumption that the electron spin only is randomized in the ${P}_{\frac{1}{2}}$ state with the nuclear spin unaffected. We show that accurate relaxation-time measurements can be made by measuring the time constants associated with the double exponentials as a function of light intensity, and extrapolating them to zero light intensity. Moreover, since no shutter is required, relaxation times ${10}^{\ensuremath{-}3}$ sec can be easily observed.