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Chinese Physics B

Enhancement of signal-to-noise ratio of ultracold polar NaCs molecular spectra by phase locking detection

Wenhao Wang, Wenliang Liu, Jizhou Wu, Yuqing Li, Xiaofeng Wang, Yanyan Liu, Jie Ma, Liantuan Xiao, Suotang Jia

Published Dec 1, 2017• 3 citations
Publisher

Abstract

We report a method of high-sensitively detecting the weak signal in photoassociation (PA) spectra of ultracold NaCs molecules by phase sensitive-demodulated trap-loss spectra of Na atoms from a photomultiplier tube. We find that the signal-to-noise ratio (SNR) of the PA spectra is strongly dependent on the integration time and the sensitivity of the lock-in amplifier, and our results show reasonable agreement with the theoretical analyses of the SNR with the demodulation parameters. Meanwhile, we investigate the effect of the interaction time of the PA laser with the colliding Na–Cs atom pairs on the SNR of the PA spectra. The atom loss rate is dependent on both the PA-induced atom loss and the loading of the MOT. The high-sensitive detection of the excited ultracold NaCs molecules lays a solid foundation for further study of the formation and application of ultracold NaCs molecules.

DOI
10.1088/1674-1056/26/12/123701

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We report on the production of ultracold heteronuclear NaCs* molecules in a dual-species magneto-optical trap through photoassociation. The electronically excited molecules are formed below the Na (3S1/2) + Cs (6P1/2) dissociation limit. 12 resonance lines are detected using trap-loss spectroscopy based on a highly sensitive modulation technique. The highest observed rovibrational level exhibits clear hyperfine structure, which is detected for the first time. This structure is simulated within a simplified model consisting of 4 coupled levels belonging to the initially unperturbed Hund’s case “a” electronic states, which have been explored in our previous work that dealt with the Na (3S1/2) + Cs (6P3/2) asymptote [W. Liu et al., Phys. Rev. A 94, 032518 (2016)].
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We report photoassociation (PA) of ultracold Na and Cs atoms in a dual-species magneto-optical trap. Trap loss spectroscopy of the ultracold polar NaCs molecules formed by PA, which carries information about relative PA transition strengths, has been experimentally obtained by using highly sensitive modulation spectroscopy technique. The fine and hyperfine effects at near-dissociation levels of NaCs molecular $c\phantom{\rule{0.16em}{0ex}}^{3}\mathrm{\ensuremath{\Sigma}}^{+}$ state are observed and modeled. The interaction Hamiltonian is described in terms of the Hund's case (aaa) coupling scheme. The molecular hyperfine structure of near-dissociation levels is simulated within a simplified model of four interacting vibrational levels belonging to different initially unperturbed electronic states. The results of the simulation infer that the interaction parameters of the observed near-dissociation levels are close to the asymptotic parameters of the pair of atoms. The coupling of the electronic states is essential for forming the hyperfine structure.
Ultracold atom photoassociation spectroscopy is significant for studying the long-range molecular potential energy structure. The signal-noise ratio of ultracold Cesium Molecule photoassociation Rovibronic Spectrum is one of the indicators as a measure of detection technology which directly affect the distinguishing ability and detection sensitivity of the spectra. We obtain an long-range ultracold cesium molecular hyperfine rovibration spectra by modulating the fluorescence spectroscopy. We find that demodulation parameters have a significant impact to the signal-noise ratio of spectra by studying the demodulation parameters such as integration time and sensitivity, which show nonlinear relation with the ratio. We achieve the optimal control of the signal-noise ratio for spectrum according to our experiment, which laid an important foundation for further studying the long-range state rovibration level of ultracold cesium molecule.
We present photoassociation spectroscopy of ultracold NaCs molecules formed in a dual-species magneto-optical trap. Excited-state molecules are formed in states correlating to the Na(3S 1/2 )+Cs(6P 3/2 ) asymptote. We assign the most prominent observed vibrational progression to the Ω=2 long range state based on a comparison with ab initio potentials. Molecules are secondarily excited before decaying to deeply bound levels of the electronic ground X 1 Σ + state where they are ionized and detected by time-of-flight mass spectroscopy.
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