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Register a new userLifetime Measurements of the $A^2Pi_{1/2}$ and $A^2Pi_{3/2}$ States in BaF
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Time resolved detection of laser induced fluorescence from pulsed excitation of electronic states in barium monofluoride (BaF) molecules has been performed in order to determine the lifetimes of the $A^2Pi_{1/2}$ and $A^2Pi_{3/2}$ states. The method permits control over experimental parameters such that systematic biases in the interpretation of the data can be controlled to below $10^{-3}$ relative accuracy. The statistically limited values for the lifetimes of the $A^2Pi_{1/2}( u=0)$ and $A^2Pi_{3/2}( u=0)$ states are 57.1(3) ns and 47.9(7)~ns, respectively. The ratio of these values is in good agreement with scaling for the different excitation energies. The investigated molecular states are of relevance for an experimental search for a permanent electric dipole moment (EDM) of the electron in BaF.
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Magneto-optically trapped atoms enable the determination of lifetimes of metastable states and higher lying excited states like the $rm{5d^{2}~^{3}F_{2}}$ state in barium. The state is efficiently populated by driving strong transitions from metastable states within the cooling cycle of the barium MOT. The lifetime is inferred from the increase of MOT fluorescence after the transfer of up to $30,%$ of the trapped atoms to this state. The radiative decay of the $rm{5d^{2}~^{3}F_{2}}$ state cascades to the cooling cycle of the MOT with a probability of $96.0(7),%$ corresponding to a trap loss of $4.0(7),%$ and its lifetime is determined to $rm{160(10)~mu s}$. This is in good agreement with the theoretically calculated lifetime of $rm{190~mu s}$ [J. Phys. B, {bf 40}, 227 (2007)]. The determined loss of $4.0(7),%$ from the cooling cycle is compared with the theoretically calculated branching ratios. This measurement extends the efficacy of trapped atoms to measure lifetimes of higher, long-lived states and validate the atomic structure calculations of heavy multi-electron systems.
Isotope shifts of the 2$p_{3/2}$-2$p_{1/2}$ transition in B-like ions are evaluated for a wide range of the nuclear charge number: Z=8-92. The calculations of the relativistic nuclear recoil and nuclear size effects are performed using a large scale configuration-interaction Dirac-Fock-Sturm method. The corresponding QED corrections are also taken into account. The results of the calculations are compared with the theoretical values obtained with other methods. The accuracy of the isotope shifts of the 2$p_{3/2}$-2$p_{1/2}$ transition in B-like ions is significantly improved.
The workhorse of atomic physics, quantum electrodynamics, is one of the best-tested theories in physics. However recent discrepancies have shed doubt on its accuracy for complex atomic systems. To facilitate the development of the theory further we aim to measure transition dipole matrix elements of metastable helium (He*) (the ideal 3 body test-bed) to the highest accuracy thus far. We have undertaken a measurement of the `tune-out wavelength which occurs when the contributions to the dynamic polarizability from all atomic transitions sum to zero; thus illuminating an atom with this wavelength of light then produces no net energy shift. This provides a strict constraint on the transition dipole matrix elements without the complication and inaccuracy of other methods. Using a novel atom-laser based technique we have made the first measurement of the tune-out wavelength in metastable helium between the $3^{3}P_{1,2,3}$ and $2^{3}P_{1,2,3}$ states at 413.07(2) nm which compares well with the predicted valuecite{Mitroy2013} of 413.02(9) nm. We have additionally developed many of the methods necessary to improve this measurement to the 100 fm level of accuracy where it will form the most accurate determination of transition rate information ever made in He* and provide a stringent test for atomic QED simulations. We believe this measurement to be one of the most sensitive ever made of an optical dipole potential, able to detect changes in potentials of $sim$200 pK and is widely applicable to other species and areas of atom optics.
We report the measurement of the photoionization cross sections of the 5S${}_{1/2}$ and 5P${}_{3/2}$ states of ${}^{87}$Rb in a two-species Hg and Rb magneto-optical trap (MOT) by the cooling laser for Hg. The photoionization cross sections of Rb in the 5S${}_{1/2}$ and 5P${}_{3/2}$ states at 253.7~nm are determined to be $1^{+4.3}_{-1}times10^{-20}~text{cm}^2$ and $4.63(30)times 10^{-18}text{cm}^2$, respectively. To measure the 5S${}_{1/2}$ and 5P${}_{3/2}$ states fractions in the MOT we detected photoionization rate of the 5P${}_{3/2}$ state by an additional 401.5~nm laser. The photoionization cross section of Rb in the 5P${}_{3/2}$ state at 401.5~nm is determined to be $text{1.18(10)}times10^{-17}~text{cm}^2$.
Ab initio calculations of QED radiative corrections to the $^2P_{1/2}$ - $^2P_{3/2}$ fine-structure transition energy are performed for selected F-like ions. These calculations are nonperturbative in $alpha Z$ and include all first-order and many-electron second-order effects in $alpha$. When compared to approximate QED computations, a notable discrepancy is found especially for F-like uranium for which the predicted self-energy contributions even differ in sign. Moreover, all deviations between theory and experiment for the $^2P_{1/2}$ - $^2P_{3/2}$ fine-structure energies of F-like ions, reported recently by Li et al., Phys. Rev. A 98, 020502(R) (2018), are resolved if their highly accurate, non-QED fine-structure values are combined with the QED corrections ab initially evaluated here.
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