Feng Zhi-Gang

Measurement of quantum defects of nS and nD states using field ionization spectroscopy in ultracold cesium atoms

This paper reports that ultracold atoms are populated into different nS and nD Rydberg states (n = 25~52) by two-photon excitation. The ionization spectrum of an ultracold Rydberg atom is acquired in a cesium magneto-optical trap by using the method of pulse field ionization. This denotes nS and nD states in the ionization spectrum and fits the data of energy levels of different Rydberg states to obtain quantum defects of nS and nD states.

Experimental Research of Spontaneous Evolution from Ultracold Rydberg Atoms to Plasma

The spontaneous evolution from ultracold Rydberg atoms to plasma is investigated in a caesium MOT by using the method of field ionization. The plasma transferred from atoms in different Rydberg states (n = 22-32) are obtained experimentally. Dependence of the threshold time of evolving to plasma and the threshold number of initial Rydberg atoms on the principal quantum number of initial Rydberg states is studied. The experimental results are in agreement with hot-cold Rydberg?Rydberg atom collision ionization theory.

Investigation of Rydberg Atomic Interaction via Collisional Loss

We present a detailed theoretically analysis of the time evolution of ultracold Rydberg atom number and effective lifetime as functions of the various parameters. We derive simple analytical formula from the existing theoretical model to estimate the strength of the Rydberg atom interaction from collisional loss rate. And estimate the strength of the dipole–dipole and van der Waals interaction from the evaluation of our recent experimental results using the present formula.

Ionization Detection of Ultracold Ground State Cesium Molecules

Photoassociation of ultracold atoms is an important method for producing stable ultracold molecules with extensive applications. Ion spectroscopy technique, which has higher sensitivity compared with trap loss spectroscopy and fragment spectroscopy, plays an important pole in the research of photoassociation spectroscopy. Based on ion spectroscopy technique, a complete experimental system is employed to produce and detect the ultracold ground state molecules, including the equipment of photoionization and time-of-fight mass spectroscopy. Ultra-cold ground state cesium molecules are demonstrated by the ionization detection technique. The number of the ground-state molecules produced in our MOT is measured. In addition, the relationship of the time interval of the cesium atom ion and the cesium molecular ion to the metal grid voltage is studied for the optimization of the experimental parameters.

Recombination during expansion of ultracold plasma

Signals of ultracold plasma are observed by two-photon ionization of laser-cooled caesium atoms in a magneto-optical 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 (~1010 cm−3) are investigated. The measured dependence on initial ion density is N1.547+0.004 at a delay time of 5 μs. 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.

Measurement of Ionization Threshold of Ultracold Cesium Rydberg Atoms in Static Electric Field

We investigate the field ionization spectra of ultracold cesium Rydberg atoms in dc electric field. The ionization thresholds of different electric fields are measured and shift of the ionization threshold relative to field-free ionization threshold is accurately described by (6.06 ± 0.14) F1/2, which is in good agreement with the classical saddle-point model for field ionization. We obtain the field-free ionization threshold of cesium (6P3/2) as 19674.89 ± 2.99 cm−1 by fitting experimental data.

Creation of an Ultracold Plasma by Photoionizing Laser-Cooled Caesium Atom

The signals of ultracold plasma are observed by two-photon ionization of laser-cooled atom in a caesium magnetooptical trap. A simple model has been introduced to explain the creation of plasma, and the mechanism is further investigated by changing the energy of a pulsed dye laser and the number of initial cooled atoms.