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Quantum Electronics and Laser Science Conference

Heteronuclear cold molecules laser spectroscopy

Gustavo Deczka Telles, M.W. Mancini, Anderson R. L. Caires, Vanderlei Salvador Bagnato, Luís Gustavo Marcassa

Published Jun 25, 2003• 0 citations
Publisher

Abstract

Summary form only given. In order to characterize the K-Cs sample we performed trap loss measurements to evaluate the heteronuclear losses introduced by the overlapped samples one to each other. We present the heteronuclear loss rate observed on a cesium magneto-optical trap (MOT) due to collisions with the cold potassium atoms as a function of the Cs trap laser intensity. The result shows that the heteronuclear collisions are not likely to compromise the MOT number and density of trapped atoms. For the regular experimental conditions, very few heteronuclear molecules are expected to be produced. Therefore, to get better signal to noise ratio we decided to apply the pulsed ion production technique. Briefly, in the experiment there are two phases: trapping and probe. During the trap phase, the heteronuclear excited quasimolecules are photoassociated and during the probe phase they are photoionized by a laser pulse. The ions are collected by a channeltron and by the time-of-flight one may distinguish between the atomic and the molecular ions. The time diagram representing the experiment is shown. By scanning the frequency of the photoassociating probe laser, we shall be able to measure the bound states of the K-Cs molecule, and then to obtain the heteronuclear scattering length.

DOI
10.1109/qels.2002.1031147

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Summary form only given. In order to characterize the K-Cs sample we performed trap loss measurements to evaluate the heteronuclear losses introduced by the overlapped samples one to each other. We present the heteronuclear loss rate observed on a cesium magneto-optical trap (MOT) due to collisions with the cold potassium atoms as a function of the Cs trap laser intensity. The result shows that the heteronuclear collisions are not likely to compromise the MOT number and density of trapped atoms. For the regular experimental conditions, very few heteronuclear molecules are expected to be produced. Therefore, to get better signal to noise ratio we decided to apply the pulsed ion production technique. Briefly, in the experiment there are two phases: trapping and probe. During the trap phase, the heteronuclear excited quasimolecules are photoassociated and during the probe phase they are photoionized by a laser pulse. The ions are collected by a channeltron and by the time-of-flight one may distinguish between the atomic and the molecular ions. The time diagram representing the experiment is shown. By scanning the frequency of the photoassociating probe laser, we shall be able to measure the bound states of the K-Cs molecule, and then to obtain the heteronuclear scattering length.
The production and research of ultracold heteronuclear molecules have aroused the great interest recently. On the one hand, these molecules are extremely popular in experiments for exploring the collision dynamic behaviors in threshold, photoassociative spectrum and strong dipole-dipole interactions. On the other hand, ultracold polar molecules populated at deeply bound levels in the singlet ground state are the right candidates to investigate quantum memories for quantum simulation, and to study strongly interacting quantum degenerate gases. The precise knowledge of cold collision processes between two different types of alkali atoms is necessary for understanding and utilizing ultracold heteronuclear molecules, sympathetic cooling, and thus formation of two species BEC. The goal of the present investigation is to study the collisions between ultracold sodium atoms and cesium atoms. We systematically demonstrate simultaneously trapping ultracold sodium and cesium atoms in a dual-species magneto-optical trap (MOT). The sodium atom trap loss rate coefficient Na-Cs is measured as a function of Na trapping laser intensity. At low intensities, the trap loss is dominated by ground-state hyperfine-changing collisions, while at high intensities, collisions involving excited atoms are more important. A strong interspecies collision-induced loss for Na atoms in the MOT is observed. In order to obtain the trap loss coefficient Na-Cs, we proceed in two steps. First, the Cs repumping laser is blocked to avoid the formation of ultraold Cs atoms. The loading process of Na atoms is recorded when the Cs trapping laser is on. Second, the loading curves of the Na atoms are obtained as Cs atoms are present with the repumping laser beams. The total losses PNa and PNa' are acquired by fitting the two loading curves of trapped Na atoms. Thus, the trap loss coefficient Na-Cs can be derived from the difference between total losses PNa and PNa' divided by the density of the Cs atoms. The coefficient Na-Cs decreases in a range of 5-10mW/cm2, which originates from the hyperfine-state changing (HFC) collision. A Doppler model is used to calculate the Na atom trap depth, in that the atom trap depth and exoergic energy determine the behavior of the collisional trap loss rate coefficient. The three corresponding calculated critical intensities of Na trapping laser are 7.98, 14.82, 16.2 mW/cm2 respectively in the Na-Cs HFC collision process. The first calculated critical intensity value agrees well with the experimental result. Our work provides a valuable insight into HFC collision between Na and Cs atoms and also paves the way for the production of ultracold NaCs molecules using Photoassociation (PA) technology. Furthermore, the experimental results lay a great basis for the obtainments of high sensitive heteronuclear NaCs molecular PA spectrum and the creation of deeply bound ground state molecules.
We report on the observation of translationally cold Cs2 molecules at temperatures in the 300–70 μK range, produced by the photoassociation of cold Cs atoms in a vapor-cell magneto-optical trap. The detection method is based on pulsed-laser photoionization of Cs2 molecules into Cs2+ ions, selectively detected through a time-of-flight mass spectrometer. This technique, together with the usual trap-loss method, enables us to perform the spectroscopy of the long-range attractive molecular states below the 6s 2S1/2+6p 2P3/2 dissociation limit.
We have observed translationally cold electronic ground-state cesium dimers produced directly in a magneto-optical trap and also by photoassociation of cold atoms in this trap. These neutral molecules were detected using photoionization and time-of-flight spectroscopy. Initial experiments indicated a cold molecular formation rate of about $600{\mathrm{s}}^{\mathrm{\ensuremath{-}}1},$ with no photoassociation laser present. The measured translational temperature of the neutral cesium dimers was approximately 100 \ensuremath{\mu}K.
We describe the experimental observation of ultracold NaCs+{\mathrm{NaCs}}^{+}NaCs+ molecular formation in a novel two-species magneto-optical trap. We interpret our observations in terms of a photoassociative ionization pathway similar to that observed in a sodium trap: $\mathrm{Na}+\mathrm{Cs}+\ensuremath{\Elzxh}{\ensuremath{\omega}}_{\mathrm{Na}}+\ensuremath{\Elzxh}{\ensuremath{\omega}}_{\mathrm{Cs}}\ensuremath{\rightarrow}{\mathrm{NaCs}}^{+}{+e}^{\ensuremath{-}}$. We have directly measured the NaCs+{\mathrm{NaCs}}^{+}NaCs+ production rate as a function of the excitation laser frequency and intensity elucidating the role of ground-state hyperfine levels. We have observed resonance structures in the frequency-dependent ion rate which we associate with the molecular character of the process.
We report on the observation of ultracold ground electric-state cesium molecules produced directly in a magneto—optical trap with a good signal-to-noise ratio. These molecules arise from the photoassociation of magneto—optical trap lasers and they are detected by resonantly enhanced multiphoton ionization technology. The production rate of ultracold cesium molecules is up to 4×10 4 s −1 . We measure the characteristic time of the ground electric-state cesium molecules generated in the experiment and investigate the Cs 2 + molecular ion intensity as a function of the trapping laser intensity and the ionization pulse laser energy. We conclude that the production of cold cesium molecules may be enhanced by using appropriate experimental parameters, which is useful for future experiments involving the production and trapping of ultracold ground electric-state molecules.
The authors have used laser cooling and trapping techniques to investigate photoionization and cold collisions. With laser-trapped Rb, they have measured the photoionization cross section from the first excited (5P) level by observing the photoionization-induced loss rate of neutral atoms from the trap. This technique has the advantage that it directly measures the photoionization rate per atom. Knowing the ionizing laser intensity and the excited-state fraction, the measured loss rate gives the absolute cross section. Using this technique, the Rb 5P photoionization cross section at {approximately}400 nm has been determined with an uncertainty of 9%. The authors are currently attempting to extend this method to the 5D level. Using time-ordered pulses of diode-laser light (similar to the STIRAP technique), they have performed very efficient two-photon excitation of trapped Rb atoms to 5D. Finally, they will present results from a recent collaboration which combines measurements form conventional molecular spectroscopy (single photon and double resonance) with photoassociation collisions of ultracold Na atoms to yield a precise ({le}1 ppm) value for the dissociation energy of the X {Sigma}{sub g}{sub +} ground state of the Na{sub 2} molecule.