Zhong Zhi-Ping

Experimental and theoretical investigations of absolute optical oscillator strengths for valence excitations of nitric oxide

The absolute optical oscillator strength density spectra of nitric oxide in the energy region of 5.0-22.0 eV have been measured by a high-resolution fast-electron energy loss spectrometer. With the calculated results obtained by the multiscattering self-consistent-field method and channel characteristics, the strongly overlapped spectra in the energy region of 7.5-9.3 eV have been analysed and the corresponding partially vibrationally resolved optical oscillator strengths have been estimated from the experimental spectra.

Measurement of the Absolute Photoionization Cross Section for the 5P3/2 State of 87Rb in a Vapor Cell Magneto-optic Trap

We report the measurement of the absolute photoionization cross section for the 5P3/2 state of 87Rb at wavelength of 473 nm, which results in the photoelectron energies of 33 meV above the ionization threshold, using cold atoms confined in a vapor-loaded magneto-optical trap. The 87Rb 5P3/2 photoionization cross section at 473 nm is determined to be σPI = 10.5 ± 2.2 Mb. Considering the spatial distribution of the trapped atoms, the average intensity of the ionization laser seen by an atom in the MOT instead of ionizing laser intensity IPI is used in our calculations for the photoionization cross sections. The excited state fraction is also accurately estimated using the latest experimental result.

An Analytical Derivation of a Symmetric Peak with Width Narrower than the Peak Width of the Probing Laser

This work provides an analytical derivation that a symmetric peak with a width narrower than that of the probing laser can appear due to the non-coherent superposition of two Fano-type peaks.

Temperature of the Remaining Cold Atoms after Two-Step Photoionization in an 87Rb Vapor Cell Magneto-Optical Trap

The temperature of the remaining cold 87Rb atoms confined in a vapor cell magneto-optical trap after two-step photoionization has been measured. In the two-step photoionization process, the first excitation laser is served by the cooling laser and the second excitation laser is served by a continuous semiconductor laser with a wavelength of 450 nm. The results show that the temperature of the remaining cold atoms decreases as the intensity of the second excitation laser increases. Moreover, the relationship between the temperature T and number N of the remaining cold atoms generally follows a power law, while it deviates from the well-known T ∝ N1/3 and the power factor is smaller than 1/3. We propose that ion-atom collisions occurring during a photoionization process strongly influence the temperature scaling law in an optically dense magneto-optical trap in the presence of an ionization laser. In addition, the forced evaporative cooling due to the combined effect of the detuning of the first excitation laser and the two-step photoionization plays a role in cooling the remaining cold atoms and results in the dependence of the power factor on the detuning of the first excitation laser.

Decay pathways of superexcited states of nitrous oxide

The ionization and ionic dissociation of the superexcited state of N2O are studied by using electron energy loss spectroscopy and positive ion time-of-flight mass spectroscopy at different momentum transfers; that is, 0 and 0.23 a.u. (atomic unit). The transitions at 13.8 eV and 14.0 eV are reassigned as 3pπ(000) and 3pσ(000) converging to A2Σ+, respectively. The competition between the main decay pathways of superexcited states at different momentum transfers is revealed. It is found that 3dσ converging to C2Σ+ mainly decays into N2O+ while 4dσ can decay into both N2O+ and NO+.

Momentum transfer dependence behaviors of ionization and dissociation of oxygen

The decay pathways of the structured ionization region of oxygen at different momentum transfers, i.e., 0, 0.23 a.u. (atomic unit), and 0.91 a.u., are studied by measuring the ion and the scattered electron coincidently. It is found that the dipole-forbidden superexcited states of (2σu)−1(c4Σ−u)npσu 3Σ−g ← X3Σ−g decay into different channels according to the principal quantum number n. The broad ridge above 35 eV, which may be due to inner-valence excited states of (2σg)−1nλ or multiply excited states, is observed both at small and large momentum transfers, and its decay channel of O++O is dominant.

Stokes identification in an atomic ensemble using a filtering system

Polarization filtering and atomic cell filtering are applied in the identification of Stokes signals in an atomic ensemble, and reduce the noise to a level of 10−5 and 10−4 respectively. Good Stokes signals are then obtained. In this article the two filtering systems and the final Stokes output are presented, and the optimization of the polarization filtering system is highlighted.

Relativistic multichannel treatment of autoionization Rydberg series of 4s2nf(n = 4 − 23) Jπ = (7/2)° for scandium

Based on relativistic multichannel theory, this paper calculates the energy levels of autoionization Rydberg series 4s2nf(n = 4 − 23)Jπ = (7/2)° of scandium at different levels of approximation within the framework of multichannel quantum defect theory. The present results show that the dipole polarizations play an important role. Considering the dynamical dipole polarization effects, this paper finds that the difference between calculated and experimental quantum defects for the 4s2nf(n = 4 − 23)Jπ = (7/2)° series is generally about 0.01–0.03. Furthermore, the reason that 4s216f is obscured in experimental spectra is suggested to be the interaction with the neighbouring resonance state converged to 3d2(1G4)of Sc+.

Relativistic Multichannel Treatment of Ionic Rydberg States of Lanthanum

Ionic Rydberg energy levels of lanthanum are calculated from first principles by relativistic multichannel theory within the framework of multichannel quantum defect theory. The present calculated results are in better agreement with the experimental measurements than the previous calculations [J. Phys. B 34 (2001) 369] due to the consideration of dynamical polarizations. Moreover, in the experimental spectra achieved by a five-laser resonance excitation via the intermediate state 5d6d3 F2, a series of weak ionic Rydberg states and some of perturbing states are found and assigned in this work.

Absolute oscillator strength densities below 100eV of N2

The absolute optical oscillator strength density (OOSD) and generalized oscillator strength densities (GOSDs) below 100eV of N2 are determined with an incident electron energy of 2500eV and an energy resolution of 100 meV. The absolute generalized oscillator strengths (GOSs) for two transitions to the superexcited states at 23 and 31.4eV are determined and their momentum transfer dependence behaviours are discussed.