Radiative lifetime of the A Π 1 / 2 2 state in RaF with relevance to laser cooling
M. Athanasakis-Kaklamanakis, Shane G. Wilkins, Pierre Lassègues, L. Lalanne, J. R. Reilly, O. Ahmad, Mia Au, Shiwei Bai, J. Berbalk, Cyril Bernerd, Anastasia Borschevsky, Alexander A. Breier, K. Chrysalidis, T. E. Cocolios, R. P. de Groote, C. M. Fajardo-Zambrano, K. T. Flanagan, S. Franchoo, R. F. García Ruíz, D. Hanstorp, Reinhard Heinke, Phillip Imgram, Á. Koszorús, Aleksandra A. Kyuberis, Jongseok Lim, Y. C. Liu, Kara Marie Lynch, Abigail McGlone, W. C. Mei, G. Neyens, L. Nies, Alexander V. Oleynichenko, A. Raggio, S. Rothe, Leonid V. Skripnikov, ERIK F. SMETS, B. van den Borne, Jessica Warbinek, Julius Wessolek, X. F. Yang
The radiative lifetime of the A Π 1 / 2 2 ( v = 0 ) state in radium monofluoride (RaF) is measured to be 35(1) ns. The lifetime of this state and the related decay rate Γ = 2.86 ( 8 ) × 10 7 s − 1 are of relevance to the laser cooling of RaF via the optically closed A Π 1 / 2 2 ← X Σ 1 / 2 2 transition, which makes the molecule a promising probe to search for new physics. RaF is found to have a comparable photon-scattering rate to homoelectronic laser-coolable molecules. Owing to its highly diagonal Franck-Condon matrix, it is expected to scatter an order of magnitude more photons than other molecules when using just three cooling lasers, before it decays to a dark state. The lifetime measurement in RaF is benchmarked by measuring the lifetime of the 8 P 3 / 2 state in Fr to be 83(3) ns, in agreement with literature. Published by the American Physical Society 2024
The radiative lifetime of the A Π 1 / 2 2 ( v = 0 ) state in radium monofluoride (RaF) is measured to be 35(1) ns. The lifetime of this state and the related decay rate Γ = 2.86 ( 8 ) × 10 7 s − 1 are of relevance to the laser cooling of RaF via the optically closed A Π 1 / 2 2 ← X Σ 1 / 2 2 transition, which makes the molecule a promising probe to search for new physics. RaF is found to have a comparable photon-scattering rate to homoelectronic laser-coolable molecules. Owing to its highly diagonal Franck-Condon matrix, it is expected to scatter an order of magnitude more photons than other molecules when using just three cooling lasers, before it decays to a dark state. The lifetime measurement in RaF is benchmarked by measuring the lifetime of the 8 P 3 / 2 state in Fr to be 83(3) ns, in agreement with literature. Published by the American Physical Society 2024
The radiative lifetime of the A 2Π1/2 (v = 0) state in radium monofluoride (RaF) is measured to be 35(1) ns. The lifetime of this state and the related decay rate Γ = 2.86(8) × 107 s−1 are of relevance to the laser cooling of RaF via the optically closed A 2Π1/2 ← X 2Σ1/2 transition, which makes the molecule a promising probe to search for new physics. RaF is found to have a comparable photon-scattering rate to homoelectronic laser-coolable molecules. Thanks to its highly diagonal Franck-Condon matrix, it is expected to scatter an order of magnitude more photons than other molecules when using just 3 cooling lasers, before it decays to a dark state. The lifetime measurement in RaF is benchmarked by measuring the lifetime of the 8P3/2 state in Fr to be 83(3) ns, in agreement with literature.
The radiative lifetime of the A2Π1/2 (v=0) state in radium monofluoride (RaF) is measured to be 35(1) ns. The lifetime of this state and the related decay rate Γ=2.86(8)×107s−1 are of relevance to the laser cooling of RaF via the optically closed A2Π1/2←X2Σ1/2 transition, which makes the molecule a promising probe to search for new physics. RaF is found to have a comparable photon-scattering rate to homoelectronic laser-coolable molecules. Thanks to its highly diagonal Franck-Condon matrix, it is expected to scatter an order of magnitude more photons than other molecules when using just 3 cooling lasers, before it decays to a dark state. The lifetime measurement in RaF is benchmarked by measuring the lifetime of the 8P3/2 state in Fr to be 83(3) ns, in agreement with literature.
The particular advantages of using the diatomic molecule radium monofluoride (RaF) as a versatile molecular probe for physics beyond the Standard Model are highlighted. i) RaF was previously suggested as being potentially amenable to direct cooling with lasers. As shown in the present work, RaF's energetically lowest electronically excited state is of 2Π symmetry (in contrast to BaF), such that no low-lying 2Δ state prevents efficient optical cooling cycles. ii) The effective electric field acting on the unpaired electron in the electronic ground state of RaF is estimated larger than in YbF, from which the best restrictions on the electron electric dipole moment (eEDM) were obtained experimentally. iii) Favourable crossings of spin-rotational levels of opposite parity in external magnetic fields exist, which are important for the measurement of the nuclear anapole moment of nuclei with a valence neutron. Thus, RaF appears currently as one of the most attractive candidates for investigation of parity-odd as well as simultaneously parity- and time-reversal-odd interactions in the realms of molecular physics.
Spectroscopic studies of aluminum monofluoride (AlF) have revealed its highly favorable properties for direct laser cooling. All Q lines of the strong A1Π ← X1Σ+ transition around 227 nm are rotationally closed and thereby suitable for the main cooling cycle. The same holds for the narrow, spin-forbidden a3Π ← X1Σ+ transition around 367 nm, which has a recoil limit in the µK range. We here report on the spectroscopic characterization of the lowest rotational levels in the a3Π state of AlF for v = 0–8 using a jet-cooled, pulsed molecular beam. An accidental AC Stark shift is observed on the a3Π0, v = 4 ← X1Σ+, v = 4 band. By using time-delayed ionization for state-selective detection of the molecules in the metastable a3Π state at different points along the molecular beam, the radiative lifetime of the a3Π1, v = 0, J = 1 level is experimentally determined as τ = 1.89 ± 0.15 ms. A laser/radio frequency multiple resonance ionization scheme is employed to determine the hyperfine splittings in the a3Π1, v = 5 level. The experimentally derived hyperfine parameters are compared to the outcome of quantum chemistry calculations. A spectral line with a width of 1.27 kHz is recorded between hyperfine levels in the a3Π, v = 0 state. These measurements benchmark the electronic potential of the a3Π state and yield accurate values for the photon scattering rate and for the elements of the Franck–Condon matrix of the a3Π–X1Σ+ system.
Polar radioactive molecules have been suggested to be exceptionally sensitive systems in the search for signatures of symmetry-violating effects in their structure. Radium monofluoride (RaF) possesses an especially attractive electronic structure for such searches, as the diagonality of its Franck-Condon matrix enables the implementation of direct laser cooling for precision experiments. To maximize the sensitivity of experiments with short-lived RaF isotopologues, the molecular beam needs to be cooled to the rovibrational ground state. Due to the high kinetic energies and internal temperature of extracted beams at radioactive ion beam (RIB) facilities, in-flight rovibrational cooling would be restricted by a limited interaction timescale. Instead, cooling techniques implemented on ions trapped within a radiofrequency quadrupole cooler-buncher can be highly efficient due to the much longer interaction times (up to seconds). In this work, the feasibility of rovibrationally cooling trapped RaF+ and RaH+ cations with repeated laser excitation is investigated. Due to the highly diagonal nature between the ionic ground state and states in the neutral system, any reduction of the internal temperature of the molecular ions would largely persist through charge-exchange without requiring the use of cryogenic buffer gas cooling. Quasirelativistic X2C and scalar-relativistic ECP calculations were performed to calculate the transition energies to excited electronic states and to study the nature of chemical bonding for both RaF+ and RaH+. The results indicate that optical manipulation of the rovibrational distribution of trapped RaF+ and RaH+ is unfeasible due to the high electronic transition energies, which lie beyond the capabilities of modern laser technology. However, more detailed calculations of the structure of RaH+ might reveal possible laser-cooling pathways.
Aluminum monofluoride (AlF) has favorable properties for laser cooling and trapping experiments. The strong A¹Π ← X¹Σ⁺ band near 227 nm and the narrow a³Π ← X¹Σ⁺ band near 367 nm have rotationally and vibrationally closed transitions, making them well-suited for efficient photon scattering. Among the states relevant to laser cooling, the a³Π state is the least characterized, as its differing spin multiplicity from the ground state makes it difficult to access experimentally. This thesis reports on the spectroscopic characterization of the a³Π state and higher triplet states of AlF. Special emphasis is placed on the interpretation of anomalies in the molecular spectra, which occur due to interactions between different electronic states. The presented experiments are performed on supersonically cooled AlF molecules in a molecular beam. Pulsed and continuous-wave dye lasers (270–570 nm) and an RF transmission line (1–500 MHz) are used for resonant excitation. The rotationally resolved spectra of the spin-forbidden a³Π ← X¹Σ⁺ band reveal that this band is weakly allowed due to the spin–orbit interaction of the a³Π state with distant singlet states. The vibrational, rotational, and spin–orbit coupling parameters of the a³Π, v = 0–7 states are extracted from these spectra. This allows the construction of an accurate electronic potential for the a³Π state and determination of the Franck–Condon matrix of the a³Π – X¹Σ⁺ system. All Λ-doublet transitions within the a³Π₁, v = 5, J = 1 level are recorded, and the hyperfine parameters of this level are determined. The observation of a spectral line with a full width at half maximum of 1.27 kHz, belonging to a hyperfine transition within the a³Π₁, v = 0 state, confirms the absence of lifetime broadening for transitions between two metastable levels. The lowest rotational levels of the A¹Π, v = 6 and b³Σ⁺, v = 5 states are nearly isoenergetic and interact via spin–orbit coupling. These strongly mixed levels provide a doorway between the singlet and triplet manifolds. These perturbed levels are characterized from hyperfine-resolved spectra. The lifetimes of selected hyperfine levels, which range from 2 ns to 200 ns depending on the degree of singlet–triplet mixing, are determined by time-delayed ionization, Lamb-dip spectroscopy, and precise analysis of transition lineshapes. Two theoretically predicted triplet states of AlF, the counterparts of the well-characterized D¹Δ and E¹Π states, had not been experimentally identified prior to this work. This thesis reports on the first characterization of the d³Π (v = 0–6) and e³Δ (v = 0–2) states, confirming the predicted energetic ordering of these states. In addition, the f³Σ⁺ (v = 0–2) states are characterized. Interestingly, the spectra of the d³Π, v = 3 ← a³Π, v = 3 band show an intensity distribution that is clearly different from that of all other diagonal bands. This band gets its weak, unexpected rotational structure due to intensity borrowing from the nearby e³Δ, v = 2 ← a³Π, v = 3 band. Analysis of this effect allows for the detailed characterization of the spin–orbit and spin–rotation interactions between the d³Π and e³Δ states.