Physical Review A

Optical properties of alkali-metal atoms in pressurized liquid helium

Toshiya Kinoshita, K. Fukuda, Yoshiro Takahashi, T. Yabuzaki

Published Oct 1, 1995• 71 citations

Abstract

The excitation and emission spectra of alkali-metal atoms (Cs and Rb) in liquid helium are studied. The helium pressure is changed from the saturated vapor pressure to about 25 atm at 1.6 K, under which conditions the liquid helium is in a superfluid state. The pressure shift and broadening of the observed spectra corresponding to the D lines are explained qualitatively by a theoretical calculation based on the spherical atomic bubble model. The Cs ${\mathit{D}}_{2}$ excitation spectra are found to have double peaks, indicating the existence of anisotropic oscillations of the bubble surface. The disappearance of the ${\mathit{D}}_{2}$ emission lines and the pressure-dependent quenching of the Rb ${\mathit{D}}_{1}$ emission lines are also discussed.

DOI: 10.1103/physreva.52.2707

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Physical Review A

Optical properties of alkali-metal atoms in pressurized liquid helium

Toshiya Kinoshita, K. Fukuda, Yoshiro Takahashi, T. Yabuzaki

Published Oct 1, 1995• 71 citations

Publisher

Abstract

{\mathit{D}}_{2}

excitation spectra are found to have double peaks, indicating the existence of anisotropic oscillations of the bubble surface. The disappearance of the

{\mathit{D}}_{2}

emission lines and the pressure-dependent quenching of the Rb

{\mathit{D}}_{1}

emission lines are also discussed.

DOI: 10.1103/physreva.52.2707

Related papers

Pressure-dependent quenching of Rb 5Pstates in liquid helium

Toshiya Kinoshita, K. Fukuda, T. Matsuura +1 more

The decay times of ${\mathit{D}}_{1}$ emission lines of Rb and Cs atoms in superfluid helium were measured at 1.6 K as functions of helium pressure in a range from the saturated vapor pressure to about 25 atm. In the case of Cs, the measured decay time is almost independent of the helium pressure and is given by the lifetime of the 6 ${\mathit{P}}_{1/2}$ state of the free atom. However, we have found that the decay time of the Rb ${\mathit{D}}_{1}$ line decreases with increasing pressure. This suggests the coexistence of two processes leading from the excited P state to the ground state, one an ordinary ${\mathit{D}}_{1}$ emission transition and the other a process decaying via a lower energy state before reaching the ground state. The pressure-dependent quenching observed only for the Rb atom can be explained by the competition of the above two processes. A possible mechanism for quenching of the Rb 5P states is discussed in terms of the interaction potentials of the alkali-metal-atom-- ${\mathrm{He}}_{\mathit{N}}$ system, where two or six helium atoms are localized near the alkali core in a particular anisotropic configuration. The dynamics of processes leading from the excited P states of Na and Cs atoms are also discussed. \textcopyright{} 1996 The American Physical Society.The decay times of ${\mathit{D}}_{1}$ emission lines of Rb and Cs atoms in superfluid helium were measured at 1.6 K as functions of helium pressure in a range from the saturated vapor pressure to about 25 atm. In the case of Cs, the measured decay time is almost independent of the helium pressure and is given by the lifetime of the 6${\mathit{P}}_{1/2}$ state of the free atom. However, we have found that the decay time of the Rb ${\mathit{D}}_{1}$ line decreases with increasing pressure. This suggests the coexistence of two processes leading from the excited P state to the ground state, one an ordinary ${\mathit{D}}_{1}$ emission transition and the other a process decaying via a lower energy state before reaching the ground state. The pressure-dependent quenching observed only for the Rb atom can be explained by the competition of the above two processes. A possible mechanism for quenching of the Rb 5P states is discussed in terms of the interaction potentials of the alkali-metal-atom--${\mathrm{He}}_{\mathit{N}}$ system, where two or six helium atoms are localized near the alkali core in a particular anisotropic configuration. The dynamics of processes leading from the excited P states of Na and Cs atoms are also discussed. \textcopyright{} 1996 The American Physical Society.

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\n\t\t\t\tA theoretical analysis of the line broadening of localized atomic transitions in liquid helium is presented. It is shown that accurate information can be derived on the long-range part of the He*-He interaction as well as on the local structure near the He* emitters. The analysis confirms that in corona discharges in liquid helium the emitting He* atoms reside in cavities and that for known He*-He interaction the size of the cavities can be deduced from the line profile. The He*-He interaction was calculated using the full configuration interaction (CI) method as implemented in the Molpro package. The widths of atomic lines due to fluorescent transitions between different excited states of helium atoms were calculated as a function of external pressure in the range from 0.1 and 3.5 MPa using the static approximation method, and the input from the results of the CI calculation and cavity diameters calculated using the bubble model. The calculated widths showed excellent agreement with experimental data of liquid helium excited by corona discharges. A second, analytical analysis using a power function to represent the He*-He interaction showed qualitative agreement with the experimental data.\n\t\t\t\n\t\t\t\tA theoretical analysis of the line broadening of localized atomic transitions in liquid helium is presented. It is shown that accurate information can be derived on the long-range part of the He*-He interaction as well as on the local structure near the He* emitters. The analysis confirms that in corona discharges in liquid helium the emitting He* atoms reside in cavities and that for known He*-He interaction the size of the cavities can be deduced from the line profile. The He*-He interaction was calculated using the full configuration interaction (CI) method as implemented in the Molpro package. The widths of atomic lines due to fluorescent transitions between different excited states of helium atoms were calculated as a function of external pressure in the range from 0.1 and 3.5 MPa using the static approximation method, and the input from the results of the CI calculation and cavity diameters calculated using the bubble model. The calculated widths showed excellent agreement with experimental data of liquid helium excited by corona discharges. A second, analytical analysis using a power function to represent the He*-He interaction showed qualitative agreement with the experimental data.\n\t\t\t

Sep 9, 20120 citations

{\mathit{D}}_{2}

excitation spectra are found to have double peaks, indicating the existence of anisotropic oscillations of the bubble surface. The disappearance of the

{\mathit{D}}_{2}

emission lines and the pressure-dependent quenching of the Rb

{\mathit{D}}_{1}

emission lines are also discussed.

The decay times of

{\mathit{D}}_{1}

emission lines of Rb and Cs atoms in superfluid helium were measured at 1.6 K as functions of helium pressure in a range from the saturated vapor pressure to about 25 atm. In the case of Cs, the measured decay time is almost independent of the helium pressure and is given by the lifetime of the 6

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

state of the free atom. However, we have found that the decay time of the Rb

{\mathit{D}}_{1}

line decreases with increasing pressure. This suggests the coexistence of two processes leading from the excited P state to the ground state, one an ordinary

{\mathit{D}}_{1}

emission transition and the other a process decaying via a lower energy state before reaching the ground state. The pressure-dependent quenching observed only for the Rb atom can be explained by the competition of the above two processes. A possible mechanism for quenching of the Rb 5P states is discussed in terms of the interaction potentials of the alkali-metal-atom--

{\mathrm{He}}_{\mathit{N}}

system, where two or six helium atoms are localized near the alkali core in a particular anisotropic configuration. The dynamics of processes leading from the excited P states of Na and Cs atoms are also discussed. \textcopyright{} 1996 The American Physical Society.

We have measured the pressure broadening and shift of the excitation and emission lines of the 6

{\mathit{s}}^{2}

^{1}

{\mathit{S}}_{0}

\ensuremath{\rightarrow}6s6p

^{1}

{\mathit{P}}_{1}

transition of Ba atoms implanted in liquid and solid helium at 1.5 K. The observed spectra are quantitatively explained within the adiabatic line-broadening theory by assuming a bubble structure of the trapping sites for the Ba atoms. The evolution of the bubble shape and size in the optical excitation-deexcitation cycle is modeled theoretically.

{\mathit{D}}_{1}

-line optical pumping of alkali-metal atoms (Cs and Rb) in superfluid helium (He II), we could achieve large spin polarization of the atoms in the ground states, more than 50% for both electron and nuclear spins, especially for the Cs atoms. The alkali-metal atoms were implanted into He II by laser sputtering. We detected optically the magnetic resonances between the ground-state Zeeman sublevels, and found that the g values and hyperfine constants in He II were the same as in vacuum within the experimental error. We discuss possible applications of these spin-polarized atoms in He II.