In this paper, ultracold atoms and molecules in a dark magneto-optical trap （MOT） are studied via depumping the cesium cold atoms into the dark hyperfine ground state. The collision rate is reduced to 0.45 s-1 and the density of the atoms is increased to 5.6 × 1011 cm-3 when the fractional population of the atoms in the bright hyperfine ground state is as low as 0.15. The vibrational spectra of the ultracold cesium molecules are also studied in a standard MOT and in a dark MOT separately. The experimental results are analyzed by using the perturbative quantum approach.
A phase-stabilized femtosecond frequency comb is used to measure high-resolution spectra of two-photon transition 62S1/2-62P1/2,3/2-82S1/2 in a cesium vapor. The broadband laser output from a femtosecond frequency comb is split into counter-propagating parts, shaped in an original way, and focused into a room-temperature cesium vapor. We obtain high-resolution two-photon spectroscopy by scanning the repetition rate of femtosecond frequency comb, and through absolute frequency measurements.
The high-resolution photoassociation spectrum of the ultracold cesium molecular 0＋ state below the 6S1/2 ＋ 6PI/2 limit is presented in this paper. The saturation of the photoassociation scattering probability is observed from the depen dence of the trap-loss probability on the photoassociation laser intensity. The corresponding resonant line width is also demonstrated to increase linearly with increasing photoassociation laser intensity. Our experimental data have good con sistency with the theoretical saturation model of Bohn and Julienne [Bohn J L and Julienne P S 1999 Phys. Rev. A 60 1].
Signals of ultracold plasma are observed by two-photon ionization of laser-cooled caesium atoms in a magnetooptical trap. Recombination of ions and electrons into Rydberg atoms during the expansion of ultracold plasma is investigated by using state-selective field ionization spectroscopy. The dependences of recombination on initial electron temperature （1 70 K） and initial ion density （-10^10 cm-3） are investigated. The measured dependence on initial ion density is N^1.547±0.004 at a delay time of 5μs. The recombination rate rapidly declines as initial electron temperature increases when delay time is increased. The distributions of Rydberg atoms on different values of principal quantum number n, i.e. n = 30-60, at an initial electron temperature of 3.3 K are also investigated. The main experimental results are approximately explained by the three-body recombination theory.
We report on the observation of enhanced high-order partial wave scattering from atom atom interaction via changing the temperature of a magneto optical trap in the process of photoassociation. The high-order scattering partial wave is directly manifested through the large signal amplitude of the rovibrational resonance levels of trap-loss spectroscopy from photoassociation.
We have produced ultracold polar RbCs molecules via photoassociation starting from laser-cooled 85Rb and 133Cs atoms in a dual−species,forced dark magneto-optical trap.The formed electronically excited RbCs∗molecules correlated to the Rb(5S_(1/2))+Cs(6P_(1/2))dissociation limit are observed by trap loss spectroscopy.Following the decay of these excited RbCs*molecules,the formed ground state molecules are directly ionized by a two-photon single-color pulse dye laser,which is a new ionization mechanism for ground state RbCs molecules and thence detected by time-of-flight mass spectroscopy.
JI Zhong-HuaZHANG Hong-ShanWU Ji-ZhouYUAN Jin-PengZHAO Yan-TingMA JieWANG Li-RongXIAO Lian-TuanJIA Suo-Tang
We propose a technique to precisely measure the line width of the photoassociation spectra of the excited cesium molecule by using a frequency shifter to generate two laser beams with a precise frequency difference. A series of photoassociation （PA） spectra are recorded with two laser beam induced molecular lines, whose peak separation serves as an accurate frequency ruler to measure the line width of the PA spectra. The full width half maximum line width was studied as a function of PA laser intensity. The extrapolated value at zero laser intensity is （34.8± 0.22） MHz. By analyzing other broadening mechanisms, a value of （32.02 ± 0.70） MHz was deduced. It is shown that this scheme is inexpensive, simple, robust, and is promising for applications in a variety of other atomic species.
Loading time is one of the most important dynamic characteristics of a magneto-optical trap. In this paper, we primarily report on a detailed experimental study of the effects of some magneto-optical trap control parameters on loading time, including the background vacuum pressure, the magnetic field gradient, and the intensities of trapping and repumping lasers. We compare the results with previous theoretical and experimental results, and give qualitative analysis. These experimental investigations offer some useful guidelines to coatrol the loading time of magneto-optical traps. The controllable loading time achieved is helpful to enhance the signal-to-noise ratio of photoassociation spectroscopy, which is remarkably improved from 7 to 28.6.
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 Cs2＋ 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.
