We report on hyperfine-resolved laser spectroscopy of the A2Π ← X2Σ+ transition of magnesium monofluoride (MgF), relevant for laser cooling. We recorded 25 rotational transitions with an absolute accuracy of better than 20 MHz, assigned 56 hyperfine lines, and determined precise rotational, fine, and hyperfine structure parameters for the A2Π state. The radiative lifetime of the A2Π state was determined to be 7.2(3) ns, in good agreement with ab initio calculations. The transition isotope shift between bosonic isotopologues of the molecule is recorded and compared to predicted values within the Born–Oppenheimer approximation. We measured the Stark effect of selected rotational lines of the A2Π ← X2Σ+ transition by applying electric fields of up to 10.6 kV cm−1 and determined the permanent electric dipole moments of 24MgF in its ground X2Σ+ and first excited A2Π states to be μX = 2.88(20) D and μA = 3.20(22) D, respectively. Based on these measurements, we caution for potential losses from the optical cycling transition due to electric field induced parity mixing in the excited state. In order to scatter 104 photons, the electric field must be controlled to below 1 V cm−1.
We report on hyperfine-resolved laser spectroscopy of the A2Π ← X2Σ+ transition of magnesium monofluoride (MgF), relevant for laser cooling. We recorded 25 rotational transitions with an absolute accuracy of better than 20 MHz, assigned 56 hyperfine lines, and determined precise rotational, fine, and hyperfine structure parameters for the A2Π state. The radiative lifetime of the A2Π state was determined to be 7.2(3) ns, in good agreement with ab initio calculations. The transition isotope shift between bosonic isotopologues of the molecule is recorded and compared to predicted values within the Born–Oppenheimer approximation. We measured the Stark effect of selected rotational lines of the A2Π ← X2Σ+ transition by applying electric fields of up to 10.6 kV cm−1 and determined the permanent electric dipole moments of 24MgF in its ground X2Σ+ and first excited A2Π states to be μX = 2.88(20) D and μA = 3.20(22) D, respectively. Based on these measurements, we caution for potential losses from the optical cycling transition due to electric field induced parity mixing in the excited state. In order to scatter 104 photons, the electric field must be controlled to below 1 V cm−1.
We report high resolution electronic spectroscopy of cold magnesium monofluoride (MgF) molecules in the gas phase, which are created by a combination of laser ablation, chemical reaction, and 6 K helium buffer-gas cooling. Thanks to the sufficient population in the low-lying rotational states, the P, Q, and R branches in the electronic transition of the X2Σ+ to A2Π state are able to be measured unambiguously by in-cell absorption spectra. For the first time, we show that the A2Π state of MgF is actually a normal state, not an inverted one. The laser cooling relevant transitions X2Σ+v=0,1,N=1→A2Π1/2(v=0,J′=1/2) are also identified, along with the hyperfine structure of the X2Σ+(v = 0, N = 1) state. This study provides an important step for ongoing laser cooling experiments of MgF molecules.
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.
Recently, we determined the detailed energy level structure of the X1Σ+, A1Π and a3Π states of AlF that are relevant to laser cooling and trapping experiments [Truppe et al., Phys. Rev. A. 100 (5), 052513 (2019)]. Here, we investigate the b3Σ+,v=0 state of the AlF molecule. A rotationally resolved (1 + 2)-REMPI spectrum of the b3Σ+,v′=0 ← a3Π, v′′=0 band is presented and the lifetime of the b3Σ+,v=0 state is measured to be 190(2) ns. Hyperfine-resolved, laser-induced fluorescence spectra of the b3Σ+,v′=0 ← X1Σ+, v′′ = 1 and the b3Σ+,v ′ = 0 ← a3Π, v′′ = 0 bands are recorded to determine fine- and hyperfine structure parameters. The interaction between the b3Σ+,v = 0 and the nearby A1Π state is studied and the magnitude of the spin–orbit coupling between the two electronic states is derived using three independent methods to give a consistent value of 10(1) cm-1. The triplet character of the A state causes an A → a loss from the main A−X laser cooling cycle below the 10-6 level.
Recently, we determined the detailed energy level structure of the X1Σ+, A1Π and a3Π states of AlF that are relevant to laser cooling and trapping experiments [Truppe et al., Phys. Rev. A. 100 (5), 052513 (2019)]. Here, we investigate the b3Σ+,v=0 state of the AlF molecule. A rotationally resolved (1 + 2)-REMPI spectrum of the b3Σ+,v′=0←a3Π,v″=0 band is presented and the lifetime of the b3Σ+,v=0 state is measured to be 190(2) ns. Hyperfine-resolved, laser-induced fluorescence spectra of the b3Σ+,v′=0←X1Σ+,v″=1 and the b3Σ+,v′=0←a3Π,v″=0 bands are recorded to determine fine- and hyperfine structure parameters. The interaction between the b3Σ+,v=0 and the nearby A1Π state is studied and the magnitude of the spin–orbit coupling between the two electronic states is derived using three independent methods to give a consistent value of 10(1) cm−1. The triplet character of the A state causes an A→a loss from the main A−X laser cooling cycle below the 10−6 level.
Abstract We present a theoretical study of the bichromatic force exerted on magnesium monofluoride (MgF), in which we have considered the complex vibrational and rotational levels and the effects of small internal splittings and degeneracies, including fine and hyperfine structures and the magnetic quantum numbers. We calculate some parameters used in the MgF molecular transitions between X 2 Σ + , A 2 Π and B 2 Σ + states. It is the first time that the radiative lifetimes of B 2 Σ + → X 2 Σ + and B 2 Σ + → A 2 Π have been derived by ab initio calculations. The detailed numerical modeling of bichromatic forces by direct numerical solution for the time-dependent density matrix is presented. Here, we propose a simplified numerical model to study the dynamic process of MgF slowing by neglecting the effect of the high vibrational levels, in which a skewed magnetic field is applied to destabilize the dark state. We deduce the relation between per-bichromatic-component irradiance I and the total Rabi frequency amplitude. We also compare our proposed simplified model with two other theoretical ones (Aldridge et al 2016 Phys. Rev. A 93 013419 ). Monte Carlo simulations show that a buffer-gas-cooled MgF beam with a forward velocity of 120 m s −1 can be decelerated nearly to several m/s within a distance of ∼0.5 cm. Comparing with the B → X transition, we find that the A → X transition in MgF is more suitable for the bichromatic force cooling and slowing.
Here we report on spectroscopic measurements of the aluminum monofluoride molecule (AlF; boson) that are relevant to laser cooling and trapping experiments. We measure the detailed energy-level structure of AlF in the $X{\phantom{\rule{0.16em}{0ex}}}^{1}{\mathrm{\ensuremath{\Sigma}}}^{+}$ electronic ground state, in the $A{\phantom{\rule{0.16em}{0ex}}}^{1}\mathrm{\ensuremath{\Pi}}$ state, and in the metastable $a{\phantom{\rule{0.16em}{0ex}}}^{3}\mathrm{\ensuremath{\Pi}}$ state. We determine the rotational, vibrational, and electronic branching ratios from the $A{\phantom{\rule{0.16em}{0ex}}}^{1}\mathrm{\ensuremath{\Pi}}$ state. We also study how the rotational levels split and shift in external electric and magnetic fields. We find that AlF is an excellent candidate for laser cooling on any Q line of the $A{\phantom{\rule{0.16em}{0ex}}}^{1}\mathrm{\ensuremath{\Pi}}$ - $X{\phantom{\rule{0.16em}{0ex}}}^{1}{\mathrm{\ensuremath{\Sigma}}}^{+}$ transition and for trapping at high densities. The energy levels in the $X{\phantom{\rule{0.16em}{0ex}}}^{1}{\mathrm{\ensuremath{\Sigma}}}^{+},v=0$ state and within each $\mathrm{\ensuremath{\Omega}}$ manifold in the $a{\phantom{\rule{0.16em}{0ex}}}^{3}\mathrm{\ensuremath{\Pi}},v=0$ state are determined with a relative accuracy of a few kHz, using laser-radio-frequency multiple resonance and ionization detection schemes in a jet-cooled, pulsed molecular beam. To determine the hyperfine and $\mathrm{\ensuremath{\Lambda}}$-doubling parameters we measure transitions throughout the 0.1-MHz--66-GHz range, between rotational levels in the $X{\phantom{\rule{0.16em}{0ex}}}^{1}{\mathrm{\ensuremath{\Sigma}}}^{+},v=0$ state, and between rotational and $\mathrm{\ensuremath{\Lambda}}$-doublet levels in all three spin-orbit manifolds of the $a{\phantom{\rule{0.16em}{0ex}}}^{3}\mathrm{\ensuremath{\Pi}},v=0$ state. We measure the hyperfine splitting in the $A{\phantom{\rule{0.16em}{0ex}}}^{1}\mathrm{\ensuremath{\Pi}}$ state using continuous wave (cw) laser-induced fluorescence spectroscopy of the $A{\phantom{\rule{0.16em}{0ex}}}^{1}\mathrm{\ensuremath{\Pi}},v=0\ensuremath{\leftarrow}X{\phantom{\rule{0.16em}{0ex}}}^{1}{\mathrm{\ensuremath{\Sigma}}}^{+},{v}^{\ensuremath{''}}=0$ band. The resolution is limited by the short radiative lifetime of the $A{\phantom{\rule{0.16em}{0ex}}}^{1}\mathrm{\ensuremath{\Pi}},v=0$ state, which we experimentally determine to be $1.90\ifmmode\pm\else\textpm\fi{}0.03$ ns. The hyperfine mixing of the lowest rotational levels in the $A{\phantom{\rule{0.16em}{0ex}}}^{1}\mathrm{\ensuremath{\Pi}}$ state causes a small loss from the main laser cooling transition of ${10}^{\ensuremath{-}5}$. The off-diagonal vibrational branching from the $A{\phantom{\rule{0.16em}{0ex}}}^{1}\mathrm{\ensuremath{\Pi}},v=0$ state is measured to be $(5.60\ifmmode\pm\else\textpm\fi{}0.02)\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}3}$ in good agreement with theoretical predictions. The strength of the spin-forbidden $A{\phantom{\rule{0.16em}{0ex}}}^{1}\mathrm{\ensuremath{\Pi}},v=0\ensuremath{\rightarrow}a{\phantom{\rule{0.16em}{0ex}}}^{3}\mathrm{\ensuremath{\Pi}},{v}^{\ensuremath{'}}=0$ transition is measured to be seven orders of magnitude lower than the strength of the $A{\phantom{\rule{0.16em}{0ex}}}^{1}\mathrm{\ensuremath{\Pi}},v=0\ensuremath{\rightarrow}X{\phantom{\rule{0.16em}{0ex}}}^{1}{\mathrm{\ensuremath{\Sigma}}}^{+},{v}^{\ensuremath{''}}=0$ transition. We determine the electric dipole moments $\ensuremath{\mu}(\mathrm{X})=1.515\ifmmode\pm\else\textpm\fi{}0.004$ Debye, $\ensuremath{\mu}(a)=1.780\ifmmode\pm\else\textpm\fi{}0.003$ Debye and $\ensuremath{\mu}(\mathrm{A})=1.45\ifmmode\pm\else\textpm\fi{}0.02$ Debye in $X{\phantom{\rule{0.16em}{0ex}}}^{1}{\mathrm{\ensuremath{\Sigma}}}^{+}$, v=0, $a{\phantom{\rule{0.16em}{0ex}}}^{3}\mathrm{\ensuremath{\Pi}},v=0$ and $A{\phantom{\rule{0.16em}{0ex}}}^{1}\mathrm{\ensuremath{\Pi}},v=0$, respectively, by recording cw laser excitation spectra in electric fields up to 150 kV/cm.