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Optics Letters

Observation of 7pP2_3/2→7dD2 optical transitions in 209 and 210 francium isotopes

Steinn Ýmir Ágústsson, G. Bianchi, R. Calabrese, L. Corradi, A. Dainelli, Alen Khanbekyan, C. Marinelli, E. Mariotti, Luca Marmugi, G. Mazzocca, L. Moi, Leonardo Ricci, Leonardo Stiaccini, L. Tomassetti

Published Sep 13, 2017• 2 citations
Publisher

Abstract

We report on the direct experimental observation of the 7pP23/2→7dD2 optical transitions in 209 and 210 francium isotopes. By continuously monitoring the fluorescence emitted by the isotopes collected in a magneto-optical trap (MOT), the electric dipole transitions 7pP23/2→7dD25/2 of Fr209, not yet experimentally observed, and 7pP23/2→7dD25/2, 7pP23/2→7dD25/2 of Fr210 were detected as sub-Doppler depletion dips of the cold atom population. This approach allowed unambiguous identification of the excited state hyperfine structures, even in the absence of a large stable vapor. Our findings demonstrate the effectiveness and the flexibility of fluorescence monitoring of trap depletion upon laser excitation, and broaden the experimental knowledge of francium isotopes and their electronic and nuclear properties. These results will have a relevant impact on ongoing researches for low-energy testing of fundamental symmetries with francium, from atomic parity non-conservation to the electron dipole moment.

DOI
10.1364/ol.42.003682

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The cooling and trapping of atoms , meaning the reduction of their average speed through the use of \nlaser techniques and their confinement in a region of a few mm3 space represents a new frontier for \nthe physics at low energies. The use of Magneto ‐ Optical Trap (MOT) for radioactive atoms allows \nthe realization of unique experiments for the study of fundamental interactions, in particular the \nstudies of Atomic Parity Non‐Conservation (APNC). This thesis presents the experimental apparatus \nused at the National Laboratories of Legnaro (LNL) of the INFN for the production and the on‐line \ntrapping of francium atoms (Fr) in a MOT. The Fr has no stable isotopes and is produced by a nuclear \nreaction, which is obtained by using Electrostatic Tandem‐XTU accelerator at LNL. The purpose of this \nline of research is the development of new techniques for trapping and detection of atoms of \nfrancium, specifically aimed at increasing the number of trapped atoms, in order to be able to make \nfuture relevant APNC measurements as a test of the Standard Model of elementary particles. The \nexperimental results achieved in the last three years (2011‐2013) will be described throughout the \nthesis, with a focus on the development of a new technique for detection of weak atomic transitions. \nThis is a direct method of investigation, based on the excitation of atoms in the MOT through a probe \nlaser beam, resonant with the transition being studied, and the detection of the transition through \nthe variations of the atomic population of the trap. Several hyperfine levels of the isotope of \nrubidium 85 have been excited by the probe beam, showing progressively lines of weaker intensity. \nThe application of this technique to radioactive atoms will allow to detect very weak transitions, such \nas those that indicate a transfer of the atoms trapped at energy levels that have not been \ninvestigated yet. The first evidence of Light‐Induced Atomic Desorption (LIAD effect) on a foil of \nyttrium, used as a neutralizer for the ionic beam of rubidium, will be presented in the thesis. It has \nbeen observed, both in the pulsed and in the continuous regimes, an increase of the MOT atomic \npopulation as a result of the desorption of the illuminated foil or the formation of the MOT when the \nyttrium foil is at room temperature and no trap is initially present. Subsequently, preliminary results \nobtained on the atomic desorption in a trap of 210Fr through a pulsed light will be shown. This \ntechnique seems to be promising to increase the atomic population of radioactive atoms traps.

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An efficient trap of {sup 221}Fr atoms

Zheng‐Tian Lu, Kristan L. Corwin, Kurt R. Vogel +1 more

Francium, the heaviest alkali, is the ideal candidate for the next generation of experiments that study atomic parity non-conversion(PNC) effects or search for a CP-violating permanent atomic electric dipole moment(EDM). Since all francium isotopes are radioactive and have half-lives of 22 minutes or less, a highly efficient atom trap is needed to provide a sufficient sample for PNC or EDM experiments. Using an improved vapor cell magneto-optical trap, we have demonstrated an efficient trap of {sup 221}Fr(t{sub {1/2}}=5m) atoms. The 4cm cube cell has a geometry optimized for a high trap loading rate and its walls are coated with dryfilm to slow the loss of francium atoms to the walls. Produced from the decay of {sup 225}Ac(t{sub {1/2}}=10d), the francium atoms are efficiently transferred into the cell using a novel orthotropic oven. We have also measured the atomic hyperfine structure of the excited 7P{sub 3/2} and 7P{sub {1/2}} levels of {sup 221}Fr.

•Dec 31, 1997•0 citations
We report on the direct experimental observation of the 7pP23/2→7dD2 optical transitions in 209 and 210 francium isotopes. By continuously monitoring the fluorescence emitted by the isotopes collected in a magneto-optical trap (MOT), the electric dipole transitions 7pP23/2→7dD25/2 of Fr209, not yet experimentally observed, and 7pP23/2→7dD25/2, 7pP23/2→7dD25/2 of Fr210 were detected as sub-Doppler depletion dips of the cold atom population. This approach allowed unambiguous identification of the excited state hyperfine structures, even in the absence of a large stable vapor. Our findings demonstrate the effectiveness and the flexibility of fluorescence monitoring of trap depletion upon laser excitation, and broaden the experimental knowledge of francium isotopes and their electronic and nuclear properties. These results will have a relevant impact on ongoing researches for low-energy testing of fundamental symmetries with francium, from atomic parity non-conservation to the electron dipole moment.
We observe the electric-dipole forbidden $7s\ensuremath{\rightarrow}8s$ transition in the francium isotopes $^{208\ensuremath{-}211}\mathrm{Fr}$ and 213Fr^{213}\mathrm{Fr}213Fr using a two-photon excitation scheme. We collect the atoms online from an accelerator and confine them in a magneto-optical trap for the measurements. In combination with previous measurements of the $7s\ensuremath{\rightarrow}7{p}_{1/2}$ transition we perform a King plot analysis. We compare the thus-determined ratio of the field shift constants (1.228 $\ifmmode\pm\else\textpm\fi{}$ 0.019) to results obtained from new ab initio calculations (1.234 $\ifmmode\pm\else\textpm\fi{}$ 0.010).
The cooling and trapping of atoms , meaning the reduction of their average speed through the use of \nlaser techniques and their confinement in a region of a few mm3 space represents a new frontier for \nthe physics at low energies. The use of Magneto ‐ Optical Trap (MOT) for radioactive atoms allows \nthe realization of unique experiments for the study of fundamental interactions, in particular the \nstudies of Atomic Parity Non‐Conservation (APNC). This thesis presents the experimental apparatus \nused at the National Laboratories of Legnaro (LNL) of the INFN for the production and the on‐line \ntrapping of francium atoms (Fr) in a MOT. The Fr has no stable isotopes and is produced by a nuclear \nreaction, which is obtained by using Electrostatic Tandem‐XTU accelerator at LNL. The purpose of this \nline of research is the development of new techniques for trapping and detection of atoms of \nfrancium, specifically aimed at increasing the number of trapped atoms, in order to be able to make \nfuture relevant APNC measurements as a test of the Standard Model of elementary particles. The \nexperimental results achieved in the last three years (2011‐2013) will be described throughout the \nthesis, with a focus on the development of a new technique for detection of weak atomic transitions. \nThis is a direct method of investigation, based on the excitation of atoms in the MOT through a probe \nlaser beam, resonant with the transition being studied, and the detection of the transition through \nthe variations of the atomic population of the trap. Several hyperfine levels of the isotope of \nrubidium 85 have been excited by the probe beam, showing progressively lines of weaker intensity. \nThe application of this technique to radioactive atoms will allow to detect very weak transitions, such \nas those that indicate a transfer of the atoms trapped at energy levels that have not been \ninvestigated yet. The first evidence of Light‐Induced Atomic Desorption (LIAD effect) on a foil of \nyttrium, used as a neutralizer for the ionic beam of rubidium, will be presented in the thesis. It has \nbeen observed, both in the pulsed and in the continuous regimes, an increase of the MOT atomic \npopulation as a result of the desorption of the illuminated foil or the formation of the MOT when the \nyttrium foil is at room temperature and no trap is initially present. Subsequently, preliminary results \nobtained on the atomic desorption in a trap of 210Fr through a pulsed light will be shown. This \ntechnique seems to be promising to increase the atomic population of radioactive atoms traps.
Francium is the least studied of the alkali atoms because it has no stable isotopes. We have performed precision spectroscopy on cold Fr atoms in a magneto optical trap. We have determined the location of the first two excited states of the S series by two-photon spectroscopy. We have measured the lifetimes of the 7p levels with a precision better than 0.5%. Our measurements test the many-body perturbation theory ab initio calculations of the dipole matrix element to very high accuracy in this relativistic alkali.
The frequency dependent polarizabilities of the francium atom are calculated from the available data of energy levels and transition rates. Magic wavelengths for the state insensitive optical dipole trapping are identified from the calculated light shifts of the 7s7s7s 2S1/2^{2}{S}_{1/2}2S1/2​, 7p7p7p 2P1/2,3/2^{2}{P}_{1/2,3/2}2P1/2,3/2​, and 8s8s8s 2S1/2^{2}{S}_{1/2}2S1/2​ levels of the 7s7s7s $^{2}{S}_{1/2}\ensuremath{-}7p$ 2P1/2,3/2^{2}{P}_{1/2,3/2}2P1/2,3/2​ and 7s7s7s $^{2}{S}_{1/2}\ensuremath{-}8s$ 2S1/2^{2}{S}_{1/2}2S1/2​ transitions, respectively. Wavelengths in the ultraviolet, visible, and near infrared region are identified that are suitable for cooling and trapping. Magic wavelengths between the 600--700 nm and 700--1000 nm regions, which are blue and red detuned with the $7s\ensuremath{-}7p$ and $7s\ensuremath{-}8s$ transitions, are feasible to implement as lasers with sufficient power are available. In addition, we calculated the tune-out wavelengths where the ac polarizability of the ground 7s7s7s 2S1/2^{2}{S}_{1/2}2S1/2​ state in francium is zero. These results are beneficial as laser cooled and trapped francium has been in use for fundamental symmetry investigations like searches for an electron permanent electric dipole moment in an atom and for atomic parity nonconservation.
Francium, the heaviest alkali, is the ideal candidate for the next generation of experiments that study atomic parity non-conversion(PNC) effects or search for a CP-violating permanent atomic electric dipole moment(EDM). Since all francium isotopes are radioactive and have half-lives of 22 minutes or less, a highly efficient atom trap is needed to provide a sufficient sample for PNC or EDM experiments. Using an improved vapor cell magneto-optical trap, we have demonstrated an efficient trap of {sup 221}Fr(t{sub {1/2}}=5m) atoms. The 4cm cube cell has a geometry optimized for a high trap loading rate and its walls are coated with dryfilm to slow the loss of francium atoms to the walls. Produced from the decay of {sup 225}Ac(t{sub {1/2}}=10d), the francium atoms are efficiently transferred into the cell using a novel orthotropic oven. We have also measured the atomic hyperfine structure of the excited 7P{sub 3/2} and 7P{sub {1/2}} levels of {sup 221}Fr.