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Register a new userVUV Fourier-transform absorption study of the Lyman and Werner bands in D2
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Authors
Arno de Lange
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An extensive survey of the D2 absorption spectrum has been performed with the high-resolution VUV Fourier-transform spectrometer of the DESIRS beamline at the SOLEIL synchrotron. The frequency range of 90 000-119 000 cm-1 covers the full depth of the potential wells of the B 1{Sigma}+u, B 1{Sigma}+u, and C 1{Pi}u electronic states up to the D(1s) + D(2ell) dissociation limit. Improved level energies of rovibrational levels have been determined up to respectively v = 51, v = 13, and v = 20. Highest resolution is achieved by probing absorption in a molecular gas jet with slit geometry, as well as in a liquid helium cooled static gas cell, resulting in line widths of ~0.35 cm-1. Extended calibration methods are employed to extract line positions of D2 lines at absolute accuracies of 0.03 cm-1. The D1{Pi}u and B 1{Sigma}+u electronic states correlate with the D(1s) + D(3ell) dissociation limit, but support a few vibrational levels below the second dissociation limit, respectively v = 0-3 and v = 0-1, and are also included in the presented study. The complete set of resulting level energies is the most comprehensive and accurate data set for D2. The observations are compared with previous studies, both experimental and theoretical.
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Accurate Fourier-transform spectroscopic absorption measurements of vacuum ultraviolet transitions in atomic nitrogen and carbon were performed at the Soleil synchrotron. For $^{14}$N transitions from the $2s^22p^3,^4$S$_{3/2}$ ground state and from the $2s^22p^3,^2$P and $^2$D metastable states were determined in the $95 - 124$ nm range at an accuracy of $0.025,mathrm{cm}^{-1}$. Combination of these results with data from previous precision laser experiments in the vacuum ultraviolet range reveal an overall and consistent offset of -0.04 wn from values reported in the NIST database. %The splitting of the $2s^22p^3,^4$S$_{3/2}$ -- %$2s2p^4,^4$P$_{5/2,3/2,1/2}$ The splittings of the $2s^22p^3,^4$S$_{3/2}$ -- $2s2p^4,^4$P$_{J}$ transitions are well-resolved for $^{14}$N and $^{15}$N and isotope shifts determined. While excitation of a $2p$ valence electron yields very small isotope shifts, excitation of a $2s$ core electron results in large isotope shifts, in agreement with theoretical predictions. For carbon six transitions from the ground $2s^22p^2,^3$P$_{J}$ and $2s^22p3s, ^3$P$_{J}$ excited states at $165$ nm are measured for both $^{12}$C and $^{13}$C isotopes.
We demonstrate a means of detecting weak optical transitions in cold atoms that undergo cyclic routines with high sensitivity. The gain in sensitivity is made by probing atoms on alternate cycles leading to a regular modulation of the ground state atom population when at the resonance frequency. The atomic transition is identified by conducting a fast Fourier transform via algorithm or instrument. We find an enhancement of detection sensitivity compared to more conventional scanning methods of $sim 20$ for the same sampling time, and can detect clock lines with fewer than $10^3$ atoms in a magneto-optical trap. We apply the method to the $(6s^{2})$ $ ^{1}S_{0} - (6s6p)$ $^{3}P_{0}$ clock transition in $^{171}$Yb and $^{173}$Yb. The ac-Stark shift of this line in $^{171}$Yb is measured to be 0.19(3) kHz$cdot$W$^{-1}cdot$m$^2$ at 556 nm.
The Ti:Saphire laser operated within 13800 - 11800 cm$^{-1}$ range was used to excite the $c^3Sigma^+$ state of KCs molecule directly from the ground $X^1Sigma^+$ state. The laser-induced fluorescence (LIF) spectra of the $c^3Sigma^+ rightarrow a^3Sigma^+$ transition were recorded with Fourier-transform spectrometer within 8000 to 10000 cm$^{-1}$ range. Overall 673 rovibronic term values belonging to both $e/f$-components of the $c^3Sigma^+(Omega=1^{pm})$ state of $^{39}$KCs, covering vibrational levels from $v$ = 0 to about 45, and rotational levels $Jin [11,149]$ were determined with the accuracy of about 0.01 cm$^{-1}$; among them 7 values for $^{41}$KCs. The experimental term values with $vin [0,22]$ were involved in a direct point-wise potential reconstruction for the $c^3Sigma^+(Omega=1^{pm})$ state, which takes into account the $Omega$-doubling effect caused by the spin-rotational interaction with the nearby $c^3Sigma^+(Omega=0^-)$ state. The analysis and interpretation were facilitated by the fully-relativistic coupled cluster calculation of the potential energy curves for the $B^1Pi$, $c^3Sigma^+$, and $b^3Pi$ states, as well as of spin-forbidden $c-X$ and spin-allowed $c-a$ transition dipole moments; radiative lifetimes and vibronic branching ratios were calculated. A comparison of relative intensity distributions measured in vibrational $c-a$ LIF progressions with their theoretical counterparts unambiguously confirms the vibrational assignment suggested in [emph{J. Szczepkovski, et. al.}, JQSRT, textbf{204}, 133-137 (2018)].
The laser induced fluorescence (LIF) spectra A1Sigma ~ b3Pi --> X1Sigma+ of KCs dimer were recorded in near infrared region by Fourier Transform Spectrometer with a resolution of 0.03 cm-1. Overall more than 200 LIF spectra were rotationally assigned to 39K133Cs and 41K133Cs isotopomers yielding with the uncertainty of 0.003-0.01 cm-1 more than 3400 rovibronic term values of the strongly mixed singlet A1Sigma+ and triplet b3Pi states. Experimental data massive starts from the lowest vibrational level v_A=0 of the singlet and nonuniformly cover the energy range from 10040 to 13250 cm-1 with rotational quantum numbers J from 7 to 225. Besides of the dominating regular A1Sigma+ ~ b3P Omega=0 interactions the weak and local heterogenous A1S+ ~ b3P Omega=1 perturbations have been discovered and analyzed. Coupled-channel deperturbation analysis of the experimental 39K133Cs e-parity termvalues of the A1S+ ~ b3P complex was accomplished in the framework of the phenomenological 4 x 4 Hamiltonian accounting implicitly for regular interactions with the remote states manifold. The resulting diabatic potential energy curves of the interacting states and relevant spin-orbit coupling matrix elements defined analytically by Expanded Morse Oscillators model reproduce 95% of experimental data field of the 39K133Cs isotopomer with a standard deviation of 0.004 cm-1 which is consistent with the uncertainty of the experiment. Reliability of the derived parameters was additionally confirmed by a good agreement between the predicted and experimental termvalues of 41K133Cs isotopomer. Calculated intensity distributions in the A ~ b --> X LIF progressions are also consistent with their experimental counterparts.
We study modulation-free methods for producing sub-Doppler, dispersive line shapes for laser stabilization near the potassium D2 transitions at 767 nm. Polarization spectroscopy is performed and a comparison is made between the use of a mirror or beam splitter for aligning the counter-propagating pump and probe beams. Conventional magnetically-induced dichroism is found to suffer from a small dispersion and large background offset. We therefore introduce a modified scheme, using two spatially separated pump-probe beam pairs. Finally we compare our results to methods using phase modulation and heterodyne detection.
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