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Physical Review

Resonant Collision Broadening of the (6s26p7s)P13∘ State in Lead

W. Happer, E. B. Saloman

Published Aug 5, 1967• 68 citations
Publisher

Abstract

Orientation and alignment depolarization cross sections have been measured for the $(6{s}^{2}6p7s){^{3}P_{1}}^{\ensuremath{\circ}}$ excited state of lead. The cross sections are characteristic of resonance collision broadening; ${\ensuremath{\sigma}}_{\mathrm{al}}=7.6\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}13}$ ${\mathrm{cm}}^{2}$ for ${v}_{\mathrm{rel}}=5\ifmmode\times\else\texttimes\fi{}{10}^{4}$ cm/sec. The ratio of orientation broadening to alignment broadening was found to be $\frac{{\ensuremath{\gamma}}_{1}}{{\ensuremath{\gamma}}_{2}}=1.21(5)$. Expressions are derived for the signal shapes in Hanle-effect, optical-double-resonance, and light-beat experiments that show which components of the signals depend on orientation and alignment relaxation times, respectively.

DOI
10.1103/physrev.160.23

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Physical Review•May 4, 1964•67 citations
Orientation and alignment depolarization cross sections have been measured for the (6s26p7s)3P1\ensuremath∘(6{s}^{2}6p7s){^{3}P_{1}}^{\ensuremath{\circ}}(6s26p7s)3P1​\ensuremath∘ excited state of lead. The cross sections are characteristic of resonance collision broadening; \ensuremathσal=7.6\ifmmode×\else\texttimes\fi10\ensuremath−13{\ensuremath{\sigma}}_{\mathrm{al}}=7.6\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}13}\ensuremathσal​=7.6\ifmmode×\else\texttimes\fi10\ensuremath−13 cm2{\mathrm{cm}}^{2}cm2 for vrel=5\ifmmode×\else\texttimes\fi104{v}_{\mathrm{rel}}=5\ifmmode\times\else\texttimes\fi{}{10}^{4}vrel​=5\ifmmode×\else\texttimes\fi104 cm/sec. The ratio of orientation broadening to alignment broadening was found to be \ensuremathγ1\ensuremathγ2=1.21(5)\frac{{\ensuremath{\gamma}}_{1}}{{\ensuremath{\gamma}}_{2}}=1.21(5)\ensuremathγ2​\ensuremathγ1​​=1.21(5). Expressions are derived for the signal shapes in Hanle-effect, optical-double-resonance, and light-beat experiments that show which components of the signals depend on orientation and alignment relaxation times, respectively.
A detailed calculation of the relaxation matrix of resonance atomic states by resonant collisions is carried out in the semiclassical impact theory. The validity of the different approximations is discussed. These results have been tested by observing self-broadening of level-crossing curves in high field and in zero field, in the 63P16^{3}P_{1}63P1​ state in mercury. Observation of these signals at high pressures is very difficult with a pure isotope because of strong absorption and trapping of resonance light in the vapor; it is made very easy by observing level-crossing signals of one isotope in a very low concentration in the vapor of another isotope. Collisions between the different pairs of mercury isotopes have been thus systematically studied. Results are in excellent agreement (10%) with theory, both for the absolute value of cross sections and for the ratio of orientation broadening to alignment broadening.
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We have experimentally investigated the anisotropy-dependent circular polarization spectra of the 133Cs^{133}\mathrm{Cs}133Cs $6s^{2}S_{1∕2}\ensuremath{\rightarrow}6p^{2}P_{3∕2}\ensuremath{\rightarrow}10s^{2}S_{1∕2}$ double-resonance transition in the presence of Ar. Satisfaction of double-resonance condition, achieved by use of a two-photon two-color pulse laser excitation scheme, was monitored by measurement of the intensity of the $9p^{2}P_{1∕2}\ensuremath{\rightarrow}6s^{2}S_{1∕2}$ cascade fluorescence at 361.73nm361.73\phantom{\rule{0.3em}{0ex}}\mathrm{nm}361.73nm. In the experiment anisotropies, namely, alignment and orientation in the 6p2P3∕26p^{2}P_{3∕2}6p2P3∕2​ level, were produced from circularly polarized light with positive helicity. Then, a circular polarization degree was measured when both lasers were circularly polarized with positive helicities, and alternately positive and negative helicities for the $6p^{2}P_{3∕2}\ensuremath{\rightarrow}10s^{2}S_{1∕2}$ transition. From the measurement, we obtained the orientation-dependent depolarization cross section in the 6p2P3∕26p^{2}P_{3∕2}6p2P3∕2​ level due to collisions with ground-level argon atoms. A disorientation cross section value of 151 (42)A˚2(42)\phantom{\rule{0.3em}{0ex}}{\mathrm{\AA{}}}^{2}(42)A˚2 is reported.
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