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Canadian Journal of Physics

Disorientation and disalignment of 42P3/2 potassium atoms, induced in resonant collisions

P. Skalinski, L. Krause

Published Oct 1, 1980• 2 citations
Publisher

Abstract

The total cross sections for disorientation (σ1) and disalignment (σ2) of 42P3/2 potassium atoms, induced in collisions with the ground-state atoms, have been determined using a modified Zeeman scanning method. Potassium vapor at densities of the order of 1011 cm−3, contained in a fluorescence cell located in a kilogauss variable magnetic field, was irradiated with circularly polarized 7665 Å resonance radiation emitted from a discharge lamp located in a constant field of 5.4 kG. Scans of the variable field permitted selective excitation of single Zeeman components in the absorbing vapor. The σ+ and σ− components of the resulting resonance fluorescence emitted parallel to the scanning field were monitored in relation to the vapor density, as were the π and σ components emitted in the perpendicular direction. As the vapor density increased so did the frequency of the collisions which caused transfers among the Zeeman states in the vapor and thus disorientation and disalignment. The observed dependence of circular and linear depolarization of the fluorescence on the potassium density yielded the cross sections σ1 = 17 × 10−12 cm2 and σ2 = 21 × 10−2 cm2, corrected for imprisonment of radiation.

DOI
10.1139/p80-194

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Physical Review A•Dec 1, 1976•13 citations
The total cross sections for disorientation (σ1) and disalignment (σ2) of 42P3/2 potassium atoms, induced in collisions with the ground-state atoms, have been determined using a modified Zeeman scanning method. Potassium vapor at densities of the order of 1011 cm−3, contained in a fluorescence cell located in a kilogauss variable magnetic field, was irradiated with circularly polarized 7665 Å resonance radiation emitted from a discharge lamp located in a constant field of 5.4 kG. Scans of the variable field permitted selective excitation of single Zeeman components in the absorbing vapor. The σ+ and σ− components of the resulting resonance fluorescence emitted parallel to the scanning field were monitored in relation to the vapor density, as were the π and σ components emitted in the perpendicular direction. As the vapor density increased so did the frequency of the collisions which caused transfers among the Zeeman states in the vapor and thus disorientation and disalignment. The observed dependence of circular and linear depolarization of the fluorescence on the potassium density yielded the cross sections σ1 = 17 × 10−12 cm2 and σ2 = 21 × 10−2 cm2, corrected for imprisonment of radiation.
A (modified) Zeeman scanning method was used to determine the cross sections for disorientation of potassium atoms in the 42P1/2 resonance substate, induced in collisions with the ground-state atoms. Potassium vapor at densities of the order of 1011 cm−3 placed in a variable magnetic field was irradiated with σ+ polarized resonance radiation of wavelength 7699 Å emitted from a discharge lamp located in a constant field of 5.4 kG. The σ+ and σ− components of the resonance fluorescence emitted at right angles to the direction of excitation were monitored in relation to the vapor density as the variable field was scanned to make the σ+ resonance transition in the absorbing vapor coincide with the σ+ component present in the exciting light. As the vapor density increased, so did the admixture of the σ− component in the fluorescent light, which arises from collisional mixing between the mJ = 1/2 and mJ = −1/2 Zeeman substates. The resulting depolarization curve yielded the disorientation cross section σ1 = 4.0 × 10−11 cm2.
The cross sections for disorientation of 42P1/2 potassium atoms, induced in collisions with noble gas atoms, have been determined in zero magnetic field by studying the depolarization of K(7699 Å) resonance fluorescence in relation to noble gas pressures. Potassium vapor at low density, mixed with a noble gas in a fluorescence vessel, was irradiated with circularly polarized 7699 Å potassium resonance radiation and the resulting resonance fluorescence, observed in an approximately backward direction, was analyzed with respect to circular polarization. The variation of the degree of polarization with gas pressure was interpreted on the basis of a 'J randomization' model for the collisions and yielded the following disorientation cross sections which are appropriately corrected for the effect of nuclear spin: K–He, 24 ± 4 Å2; K–Ne, 21 ± 3 Å2; K–Ar, 37 ± 5 Å2; K–Kr, 51 ± 7 Å2; K–Xe, 69 ± 9 Å2. The cross sections are significantly smaller than values obtained previously in kilogauss fields.
The cross sections for the decay of circular and of linear polarization in oriented 42P324^{2}P_{\frac{3}{2}}42P23​​ potassium atoms, induced in collision with inert-gas atoms, were determined in a series of fluorescence experiments. A modified Zeeman scanning method was used to populate selectively the mJ{m}_{J}mJ​ sublevels of the 2P32^{2}P_{\frac{3}{2}}2P23​​ potassium atoms mixed with inert gases and placed in a strong magnetic field. Measurements of depolarization of the fluorescence, in relation to gas pressures, yielded the following depolarization cross sections: ${\ensuremath{\sigma}}_{1}$ (disorientation): K-He, 86 A˚2{\mathrm{\AA{}}}^{2}A˚2; K-Ne, 86 A˚2{\mathrm{\AA{}}}^{2}A˚2; K-Ar, 164 A˚2{\mathrm{\AA{}}}^{2}A˚2; K-Kr, 248 A˚2{\mathrm{\AA{}}}^{2}A˚2; K-Xe, 251 \AA{}. ${\ensuremath{\sigma}}_{2}$ (disalignment): K-He, 127 \AA{}; K-Ne, 120 A˚2{\mathrm{\AA{}}}^{2}A˚2; K-Ar, 240 A˚2{\mathrm{\AA{}}}^{2}A˚2, K-Kr, 301 A˚2{\mathrm{\AA{}}}^{2}A˚2, K-Xe, 336 A˚2{\mathrm{\AA{}}}^{2}A˚2. The experimental values are in satisfactory agreement with the calculations of Nikitin and Ovchinnikova.
The mj mixing cross section for disorientation of magnetically 2 oriented potassium atoms in the 4 ^2/2 state» induced by collisions with ground state helium atoms, was measured using a modified Zeeman scanning technique.The mj substates of potassium atoms, situated in a strong magnetic field, were selectively excited and the collisionally induced mixing manifested itself by the depolarization of the potassium resonance fluorescence.The depolarization measurements yielded mixing cross -14 2 -14 2 sections ranging from 0.77 x 10 cm to 1.4 x 10 cm .It is felt that this discrepancy may be due to a selection rule for transitions between the fine structure states such that £nij = 0 is preferred.
The magnetic field dependence of the cross sections for the disorientation of 62P126^{2}P_{\frac{1}{2}}62P21​​ cesium atoms, induced in Cs-He collisions, has been studied using Zeeman scanning techniques. A Cs-He mixture, contained in a fluorescence cell which was located in a magnetic field variable from 0 to 10 kG, was irradiated with the circularly polarized 8943-\AA{} component of cesium resonance radiation in a direction parallel to the field, and the polarization of the resonance fluorescence was monitored in the backward direction in relation to the helium pressure and to the magnetic field strength. The cross sections, which are in good agreement with the results obtained previously at high and low magnetic fields, exhibit a variation with the magnetic field, which is in accordance with theoretical predictions.
Cross sections for relaxation of circular and linear polarization of 62P326^{2}P_{\frac{3}{2}}62P23​​ cesium atoms, induced in collisions with ground-state He, Ne, Ar, and Xe, have been determined by Zeeman scanning techniques. A fluorescence cell containing low-pressure cesium vapor together with a buffer gas was irradiated with circularly or linearly polarized 8521-\AA{} Cs resonance radiation, producing excited and polarized Cs atoms which became depolarized in subsequent collisions with the buffer-gas atoms. The resulting depolarization of the cesium resonance fluorescence was monitored in relation to buffer-gas pressure (0-10 Torr) and to the strength of the ambient magnetic field (0-10 kG). At low fields at which the nuclear spin $\stackrel{\ensuremath{\rightarrow}}{\mathrm{I}}$ is coupled to the electronic angular momentum $\stackrel{\ensuremath{\rightarrow}}{\mathrm{J}}$, the measurements yielded depolarization cross sections Q(circ.)Q(\mathrm{circ}.)Q(circ.) and Q(lin.)Q(\mathrm{lin}.)Q(lin.), which agree within experimental error with theoretical values calculated for spin-coupled conditions. At kilogauss fields with $\stackrel{\ensuremath{\rightarrow}}{\mathrm{I}}$ and $\stackrel{\ensuremath{\rightarrow}}{\mathrm{J}}$ decoupled, the experiments produced cross sections for disorientation and disalignment, which are also in satisfactory agreement with the appropriate theoretical predictions. The results indicate that the nuclear spin has a more pronounced effect on the collisional relaxation of the atomic dipole than of the quadrupole.