Xu Xiang-Yuan

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.

STUDY OF HIGH-LYING EXCITED STATES OF RARE-EARTH ELEMENT Dy BY LASER RESONANCE IONIZATION SPECTROSCOPY

This paper describes the investigation of high-excited states of Dy, which includes the measurement of high Rydberg states and autoionizing states, by means of laser resonance ionization spectroscopy (LRIS). Two high Rydberg series (n> 40), 4f10(5I8) 6sns and 4f10(5I8) 6snd, have been obtained by exciting the state of 4f10(5I8) 6s6p (3P20)5I80 using two-step laser excitation-electric field ionization method. With the data obtained, we determined the first ionization potential of Dy. It is 47901.7 ± 0.6 cm-1, that is, about one order more accurate than the results given in the literature. Using the same technique, we found 97 autoionizing states by exciting the state of 4f95d6s (7H70).

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.

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.

Theoretical analysis of ionic autoionization spectra of lanthanum in the energy region of 90650-91500 cm-1

Eigenquantum defects µα and transformation matrix Uiα of La+ are calculated from the first principles by relativistic multichannel theory, and dipole matrix elements Dα are obtained by fitting the experimental spectra. With these parameters, ionic autoionization spectra of lanthanum via an intermediate state (Xe)5d6d 1P1 of La+ in the energy region of 90650-91500 cm -1 are calculated within the framework of multichannel quantum defect theory. Our calculated spectra are in general agreement with the experimental data.

Autoionizing Distribution of the Triply Excited Double Rydberg States in La Atom

The autoionization distribution of the triply excited double Rydberg states (TEDRS) 5d5/2N Lnl (N ≤ 22; n ≤ 50; L, l < 4) of La has been investigated by using five-laser resonance excitation in combination with a method of sequential ionization by a pulsed electric field and a constant electric field. The experimental results exhibit that the La atoms in TEDRS predominantly single-autoionize to the ionic Rydberg states located in a few Rydberg manifolds. Furthermore, a difference of autoionization mechanisms between TEDRS above and those below the double ionization threshold is found.

A NEW EXPERIMENTAL METHOD IN THE STUDY OF IONIC RYDBERG STATES BY RESONANCE IONIZATION MASS SPECTROSCOPY

We report a new method for detecting highly excited ions. With a strong constant electric field ionization following the extracting of ions by a pulsed electric field in a time-of-flight mass spectrometer, the direct multi-photon ionization background can be eliminated in laser multi-step resonance ionization mass spectroscopy of ionic Rydberg states. A high detection efficiency can be obtained for low members of ionic Rydberg states by use of this method. We have applied the method in the study of the spectroscopy of ionic Rydberg states in ytterbium.

Autoionizing Process of the Double Rydberg State

Using five-laser resonance excitation and double time-of-flight spectroscopy, the double Rydberg states N Lnl (N ≤ 66;n ≤ 85;L, l < 4) of Ca have been obtained. The distribution of Ca+ Rydberg states, which is from the autoionization of the double Rydberg state has been measured. A novel result has been observed.

NEW AUTOIONIZING STATES NEAR THE FIRST IONIZATION LIMIT OF RARE EARTH ELEMENT Dy

This paper describes the investigation of autoionizing states near the first ionization limit of rare-earth element Dy. The 62, 51, 97 and 25 new autoionizing states resulting from the states of 4f10(5I8)6s6p(3P20) 3I70, 4f9(6H0)5d2(3F) (8G0)6s9G70, 4f9(6F0)5d6s2 7H70 and 4f95d6s2 7K70, respectively, were found by using a laser resonance ionization time-of-flight mass spectrometer (LRI-TOFMS). The photoionization efficiencies for different channels were compared with each other. In addition, the Shore-Fano parameters of autoionizing states were determined by a nonlinear fitting program.