Hong-Ping Liu

Core effect in the Stark spectrum of highly excited barium

We have studied the Stark spectrum of highly excited barium both experimentally and theoretically. The observed spectra are well explained by diagonalization of the Hamiltonian incorporating core effects. Core effects were studied by examining the Stark maps of barium as well as by comparing Stark spectra of hydrogen and barium directly. An anti-crossing is revealed by the Stark maps. The core-induced interaction between the neighboring channels of p state results in level anti-crossing, providing an efficient way of populating the neighboring states inaccessible at free field.

Exploring tunneling time by instantaneous ionization rate in strong-field ionization

A quantum approach is presented to investigate tunneling time by supervising the instantaneous ionization rate. We find that the ionization rate peak appearance lags behind the maximum of electric field intensity for a linearly polarized pulse. This time delay interval can be taken to characterize the tunneling time. In addition, if an atom with anisotropic electronic distribution is exposed to a circular polarized pulse, the tunneling time can also be measured and defined as the time difference between the instant of the largest ionization rate and the moment when the electric field points in the maximum of the bound electron density.

Laser frequency offset-locking using electromagnetically induced transparency spectroscopy of 85Rb in magnetic field

We have experimentally offset-locked the frequencies of two lasers using electromagnetically induced transparency (EIT) spectroscopy of 85Rb vapor with a buffer gas in a magnetic field at room temperature. The magnetic field is generated by a permanent magnet mounted on a translation stage and its field magnitude can be varied by adjusting the distance between the magnet and Rb cell, which maps the laser locking frequency to the space position of the magnet. This frequency–space mapping technique provides an unambiguous daily laser frequency detuning operation with high accuracy. A repeatability of less than 0.5 MHz is achieved with the locking frequency detuned up to 184 MHz when the magnetic field varies from 0 up to 80 G.

High quality electromagnetically induced transparency spectroscopy of 87Rb in a buffer gas cell with a magnetic field

We have studied the phenomenon of electromagnetically induced transparency (EIT) of 87Rb vapor with a buffer gas in a magnetic field at room temperature. It is found that the spectral lines caused by the velocity selective optical pump effects get much weaker and wider when the sample cell mixed with a 5-Torr N2 gas while the EIT signal kept almost unchanged. A weighted least-square fit is also developed to remove the Doppler broadening completely. This spectral method provides a way to measure the Zeeman splitting with high resolution, for example, the {\Lambda}-type EIT resonance splits into four peaks on the D2 line of 87Rb in the thermal 2-cm vapor cell with a magnetic field along the electric field of the linearly polarized coupling laser. The high resolution spectrum can be used to lock the laser to a given frequency by tuning the magnetic field.We have studied the phenomenon of electromagnetically induced transparency (EIT) of 87Rb vapor with a buffer gas in a magnetic field at room temperature. It is found that the spectral lines caused by the velocity selective optical pump effects get much weaker and wider when the sample cell is mixed with a 5-Torr N2 gas while the EIT signal is kept almost unchanged. A weighted least-square fit is also developed to remove the Doppler broadening completely. This spectral method provides a way to measure the Zeeman splitting with high resolution, for example, the Λ-type EIT resonance splits into four peaks on the D2 line of 87Rb in the thermal 2-cm vapor cell with a magnetic field along the electric field of the linearly polarized coupling laser. The high-resolution spectrum can be used to lock the laser to a given frequency by tuning the magnetic field.

Theoretical simulation of 87Rb absorption spectrum in a thermal cell

In this paper, we present a theoretical simulation of 87Rb absorption spectrum in a thermal cm-cell which is adaptive to the experimental observation. In experiment, the coupling and probe beams are configured to copropagate but perpendicular polarized, making up to five velocity selective optical pumping (VSOP) absorption dips able to be identified. A

Wave-function visualization of core-induced interaction of a non-hydrogenic Rydberg atom in an electric field

\Lambda

Classical Aspects in Above-Threshold Ionization with a Midinfrared Strong Laser Field

-type electromagnetically induced transparency (EIT) is also observed for each group of velocity-selected atoms. The spectrum by only sweeping the probe beam can be decomposed into a combination of Doppler-broadened background and three VSOP dips for each group of velocity-selected atoms, companied by an EIT peak. This proposed theoretical model can be used to simulate the spectrum adaptive to the experimental observation by non-linear least-square fit method. The fit for high quality of experimental observation can determine valuable transition parameters such as decaying rates and coupling beam power accurately.

Structure Effects in Angle-Resolved High-Order Above-Threshold Ionization of Molecules

In this paper we report a wave-function visualization of the core-induced interaction of a non-hydrogenic Rydberg atom in an electric field and its resultant redistribution of the spectral line intensities. The energy levels and oscillator strengths are calculated based on an effective potential where the radial part of the wavefunction is expanded in a B-spline basis. The calculation is in good agreement with the experimental measurements of the absorption spectrum of sodium atoms in an electric field of F = 840 V/cm, both below and above the saddle point Esp. The visualization of the wavefunction for the eigenstates can help us to see how they stem from the interaction between two or more red and blue hydrogenic states. An approximate localized symmetry close to the atomic core is also observed in the wavefunctions, which accounts for the alternation of oscillator strengths in the experiment.