The paper considers collisions involving spin polarized alkali Na and Cs atoms in the ground state. The complex cross sections for spin exchange and the elastic scattering cross sections of the considered atoms are calculated in the energy range from 10–4 to 10–2 a.u.

The calculation of the frequency shifts of the magnetic resonance of K and Li atoms in a K-Li mixture has been carried out. A significant difference in the behavior of the temperature dependences of the frequency shifts for the optical orientation of K or Li atoms is established. Keywords: spin exchange, cross sections, frequency shifts.

Collisions between sodium and potassium atom in the conditions of optical orientation of potassium atoms are considered. Because of collisions, the spin exchange occurs between colliding atoms, which leads to a magnetic resonance frequency shift of Na atoms. Calculations reveal that the magnetic resonance frequency shift of Na atoms in the upper hyperfine state ( F = 2) changes its sign from negative to positive upon an increase in the temperature in the absorption chamber from 300 to 500 K and passes through zero near temperature T ~ 450 K, while the frequency shift of the lower hyperfine state ( F = 1) remains negative in the entire range of investigated temperatures. An analogous effect is observed for the first time in the case in which the main contribution to the magnetic resonance frequency shift comes from the spin exchange.

The calculation of the frequency shifts of the magnetic resonance of K and Li atoms in a K-Li mixture has been carried out. A significant difference in the behavior of the temperature dependences of the frequency shifts for the optical orientation of K or Li atoms is established.

Рассмотрено взаимодействие двух поляризованных атомов лития (7Li). При столкновении таких атомов наряду с упругим рассеянием имеет место процесс спинового обмена, т. е. обмен электронной поляризацией между сталкивающимися атомами. Одновременно с переносом поляризации процесс спинового обмена приводит к сдвигу частоты магнитного резонанса сталкивающихся атомов. На основании данных по потенциалам взаимодействия между двумя атомами лития впервые проведен расчет энергетических зависимостей сечений спинового обмена и сдвига частоты магнитного резонанса. Ключевые слова: спиновый обмен, поперечные сечения, сдвиги частоты.

Рассмотрены столкновения между атомами натрия и калия в условиях оптической ориентации атомов калия. В результате столкновений происходит спиновый обмен между сталкивающимися атомами, что приводит к сдвигу частоты магнитного резонанса атомов. Проведенные расчеты показали, что сдвиг частоты магнитного резонанса атомов Na в верхнем сверхтонком состоянии ( F=2) при росте температуры в камере поглощения от 300 до 500 K меняет знак с отрицательного на положительный и проходит через нуль в окрестностях температуры T~450 K, в то время как сдвиг частоты нижнего сверхтонкого состояния ( F=1) остается отрицательным во всем диапазоне исследуемых температур. Подобного рода явление обнаружено впервые для случая, когда основной вклад в величину сдвига частоты магнитного резонанса вносит спиновый обмен. Ключевые слова: спиновый обмен, поперечные сечения, сдвиги частоты магнитного резонанса.

Collisions of alkali atoms in the ground state are accompanied by the exchange of electron polarization between the colliding atoms, which lead to the polarization transfer between particles. As a result of this process, the electronic orientation is transferred from the spin oriented atoms to unpolarized atoms, along with the polarization transfer, the magnetic resonance frequency shifts of polarized atoms occur too. In this work the magnetic resonance frequency shifts of arising from spin exchange collisions in a mixture of alkali potassium and rubidium atoms at the optical orientation of atoms are calculated. The situation when optical pumping by resonant polarized radiation is carried out only for atoms of the one kind is considered. The spin exchange process between alkali atoms was described in the formalism of the complex cross section for spin exchange process. The real and imaginary parts of the complex cross section were calculated using the interaction potentials of alkali atom dimers. The calculation of the frequency shifts is carried out on the basis of data on the interaction potentials for the following pairs of alkali atoms K-K, K-Rb and Rb-Rb. Maxwell averaging of the cross sections over the velocities was done and the temperature dependences of the magnetic resonance frequency shifts for K and Rb atoms were plotted.

The cross section and frequency shift of the magnetic resonance line for the spin exchange are calculated for a collision of lithium and cesium atoms in the ground state. The calculation was carried out on the basis of data on the singlet (X1Sigma+) and triplet (a3Sigma+) interaction potentials of the 7Li133Cs dimer. The transfer from the energy to the temperature dependence of the real and imaginary parts of the complex cross sections for a spin exchange allows us to obtain information both the broadening of the magnetic resonance line of the atoms under study and the frequency shift of the magnetic resonance upon their collision.

The spin-exchange cross sections and the magnetic resonance frequency shift in collision of lithium and cesium atoms in the ground state are calculated. The calculations are performed based on the data on the singlet ($$X{}^{1}{{\Sigma }^{ + }}$$) and triplet ($$a{}^{3}{{\Sigma }^{ + }}$$) interaction potentials of 7Li 133Cs dimer. The passage from the energy dependences of the real and imaginary parts of the complex spin-exchange cross section to the temperature dependences makes it possible to obtain information on both the broadening and the frequency shift of the magnetic resonance line in collisions of the atoms under study.

The magnetic-resonance frequency shifts of Cs and K atoms induced by spin exchange at optical orientation of atoms are calculated. The situation under study is characteristic of a tandem magnetometer based on a mixture of cesium and potassium atoms in one working chamber.

Рассчитаны сдвиги частоты магнитного резонанса атомов Cs и K, обусловленные спиновым обменом в условиях оптической ориентации атомов. Изучаемая ситуация характерна для случая тандемного магнитометра на смеси атомов цезия и калия, находящихся в одной рабочей камере. Ключевые слова: спиновый обмен, поперечные сечения, сдвиги частоты магнитного резонанса.

Spin exchange is one of the effective processes for obtaining spin-polarized atoms. Such mechanism of spin polarization is usually used to transmit and observe the longitudinal (along magnetic field) component magnetization of atoms. However, spin-exchange collisions can also lead to the transfer of the transverse component of magnetization, which occurs when the atoms involved in the collisions are exposed to an alternating resonant magnetic field. This article describes experiments to observe the transmission of transverse magnetization between alkali metal atoms Cs-133 and Rb-85 in spin-exchange collisions. The calculation of the spin exchange in a mixture of Cs and Rb under magnetic resonance conditions gave a qualitative agreement with the experimental results.

AbstractSpin-exchange cross sections and the magnetic-resonance frequency shift in collision of lithium and potassium atoms in the ground state have been calculated for the first time. The cross sections are calculated based on the data on the singlet ( $$X{}^{1}{{\Sigma }^{ + }}$$ ) and triplet ( $$a{}^{3}{{\Sigma }^{ + }}$$ ) interaction potentials of ^39K^7Li dimer. A passage from the energy dependences to the temperature ones of the real and imaginary parts of the complex spin-exchange cross section yields information about both the broadening of the magnetic resonance line of the atoms under study and the magnetic-resonance frequency shift in their collision.

Spin-exchange cross sections and the magnetic-resonance frequency shift in collision of lithium and potassium atoms in the ground state have been calculated for the first time. The cross sections are calculated based on the data on the singlet ($$X{}^{1}{{\Sigma }^{ + }}$$) and triplet ($$a{}^{3}{{\Sigma }^{ + }}$$) interaction potentials of 39K7Li dimer. A passage from the energy dependences to the temperature ones of the real and imaginary parts of the complex spin-exchange cross section yields information about both the broadening of the magnetic resonance line of the atoms under study and the magnetic-resonance frequency shift in their collision.

AbstractAn experiment on the observation of the effect of transmitting the transverse spin magnetization in spin-exchange collisions of cesium atoms with optically aligned rubidium atoms is described.

The interaction of spin-polarized cesium atoms with cesium and rubidium atoms under conditions of optical orientation of atoms is considered. On the basis of data on spin-exchange complex cross sections in the Cs–Cs and Cs–Rb systems, a calculation of a magnetic resonance frequency shift of cesium atoms in a Cs–Rb mixture, as well as comparison of the calculated values of the frequency shift with experimental data, is performed.

Collisions of alkali-metal atoms in the ground state with the electron spin S = 1/2 are accompanied by exchange of electron coordinates between colliding particles, which leads to polarization transfer between them ( i.e., to the well-known phenomenon of spin exchange). In addition, along with the polarization transfer from one partner to another, the magnetic resonance lines of colliding atoms are broadened and shifted in spin-exchange collisions. In particular the last two processes depend on the complex spin-exchange cross section. The real part of the cross section determines the so-called "spin-exchange cross section," which is responsible for the broadening of magnetic resonance lines, while the imaginary part determines the shift cross section, which governs the frequency shift of magnetic resonance. In order to describe the spin-exchange process one have to know complex spin-exchange cross sections. Complex spin-exchange cross sections are calculated on the basis of the data on the singlet ( X-1 Sigma(+)) and triplet (a(3)Sigma(+)) potentials describing the interaction alkali-metal atoms in the ground state. Collisions of alkali-metal atoms Cs, Rb, K, Na in the ground state are considered in the energy interval of 10(-4)-10(-2) au.

Сдвиги частоты магнитного резонанса спин-поляризованных атомов цезия в смеси Cs-Rb

The optical orientation of the angular momenta of alkali atoms in the presence of a buffer gas (molecular nitrogen) has been studied experimentally. It has been shown that, even at a low concentration of molecular nitrogen in the cell, the excitation of 133 Cs atoms from the lower hyperfine level with F = 3, which belongs to the ground 2 S 1/2 state, results in a larger amplitude of the magnetic resonance than the excitation from the hyperfine level with F = 4. This result has been theoretically explained under the assumption that the spin state of the alkali atomic nucleus does not change at collision with a nitrogen molecule, which is accompanied by a nonradiative transition of the alkali atom from the excited 2 P 1/2 state to the ground 2 S 1/2 state.

An experiment on the observation of the effect of transmitting the transverse spin magnetization in spin-exchange collisions of cesium atoms with optically aligned rubidium atoms is described.