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arXiv:physics/0506232 · Physical Review A

State-selective detection of near-dissociation ultracold KRb X Σ + 1 and a Σ + 3 molecules

Dajun Wang, Edward E. Eyler, P. L. Gould, William C. Stwalley

Published Sep 13, 2005• 28 citations
arXivHTMLPDF

Abstract

We report on the state-selective detection of near-dissociation ultracold KRb molecules in the ground $X\phantom{\rule{0.2em}{0ex}}^{1}\ensuremath{\Sigma}^{+}$ state and the metastable $a\phantom{\rule{0.2em}{0ex}}^{3}\ensuremath{\Sigma}^{+}$ state. The molecules are produced by photoassociation of ultracold atoms followed by radiative decay into high vibrational levels of the $X$ and $a$ states. Detection utilizes resonance-enhanced one-color two-photon ionization, followed by time-of-flight mass spectroscopy. Scanning the detection laser frequency over the range $582--625\phantom{\rule{0.3em}{0ex}}\mathrm{nm}$, we observe transitions from the ${v}^{\ensuremath{''}}=86--92$ levels of the $X$ state, which are bound by up to $30\phantom{\rule{0.3em}{0ex}}{\mathrm{cm}}^{\ensuremath{-}1}$, and the ${v}^{\ensuremath{''}}=17--23$ levels of the $a$ state, which are also bound by up to $30\phantom{\rule{0.3em}{0ex}}{\mathrm{cm}}^{\ensuremath{-}1}$. The measured vibrational spacings are in excellent agreement with those previously measured and those calculated from the relevant potential curves. Relative vibrational populations are also consistent with Franck-Condon factors for decay from the photoassociated levels.

DOI
10.1103/physreva.72.032502

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This thesis describes the spectroscopy work on ultracold 39K 85Rb molecules as part of our effort towards producing ground-state ultracold polar molecules. ^ The starting points of our experiment are laser cooled and trapped K and Rb atoms in dual-species MOTs and the molecule formation method is photoassociation (PA). A fraction of the PA-produced excited-state molecules can spontaneously emit to the two lowest electronic states, the X 1Σ + state and the a 3Σ + state, to form high vibrational level molecules. In order to develop a population transfer scheme to make deeply bound molecules, we have studied the spectroscopy of KRb in several steps. Besides the PA step, we have also carried out a state-selective detection experiment to study the population distribution of the high vibrational level molecules formed via spontaneous emission. The detection method is pulsed-laser based ion time-of-flight mass spectroscopy. Due to the linewidth limitations of the pulsed laser, this detection method can only resolve vibrational structures. A cw laser induced ion depletion spectroscopy technique has been developed in order to obtain rotational resolution. Using this ion depletion method, we have studied a possible stimulated Raman transfer scheme via the 3 1Σ+ state. To this end, we have obtained all the spectroscopic information required to produce deeply bound KRb molecules in a single vibrational and rotational level. ^ Several other spectroscopic studies using the high vibrational level ultracold molecules are also discussed. ^
Convenient state-selective detection methods are proposed for exploring triplet Rydberg states from the metastable a 3 Σ + state of ultracold KRb molecules by resonance-enhanced two-photon ionization and time-of-flight (TOF) mass spectroscopy. This would allow the first accurate determination of the ionization potential. Particularly suitable resonant intermediate states include the 2 3 Π Ω , 3 3 Σ + and 4 3 Σ + states, and we report spectroscopic studies of these states. For the 2 3 Π Ω state, the spin–orbit components (Ω = 0 + , 0 − , 1 and 2) have been investigated and a shallow long-range state (5(0 + )) at ∼ 9.3 Å has been observed. We compare our observations of these three states with predictions based on ab initio potential energy curves. Such studies may also permit the direct observation of autoionizing resonances leading to efficient formation of low-lying rovibrational levels of the 2 Σ + ground state of KRb + , ideally in the v + = 0, N + = 0 level.