Zhizhan Xu

Effects of spontaneous emission-induced coherence on population inversion in a ladder-type atomic system

Spontaneous emission can create coherence in a ladder-type three-level atom with equispaced levels, subject to the condition that the atomic dipole moments are nonorthogonal. We study the effects of this kind of coherence on the steady-state population inversion in the atomic system. We show that the population inversion can be greatly enhanced on one of the optical transitions due to the spontaneous emission-induced coherence. Furthermore, we find, within suitable parameters regions, that such coherence can also lead to unexpected population inversion on both of the optical transitions.

Atom localization via interference of dark resonances

A scheme of atom localization based on the interference of resonance of double-dark states is proposed, in which the atom interacts with a classical standing-wave field. It is found that the localization property is significantly improved due to the interaction of double-dark resonances. It is realized that the atom is localized just at the nodes of the standing-wave field with higher precision. Moreover, an improvement by a factor of 2 in the detecting probability of a single atom within the subwavelength domain can be achieved by adjusting the probe-field detuning. This scheme shows more advantages than other schemes of atom localization.

Sudden death and birth of entanglement beyond the Markovian approximation

Abstract We investigate the entanglement dynamics of two initially entangled qubits interacting independently with two uncorrelated reservoirs beyond the Markovian approximation. Quite different from the Markovian reservoirs [C.E. Lopez, et al., Phys. Rev. Lett. 101 (2008) 080503], we find that entanglement sudden birth (ESB) of the two reservoirs occurs without certain symmetry with respect to the entanglement sudden death (ESD) of the two qubits. A phenomenological interpretation of entanglement revival is also given.

Optical nonlinear properties and optical limiting for [(n-Bu)4N]4[MoS4Cu]4

We report the nonlinear optical properties of one metal cluster [(n-Bu)4N]4[MoS4Cu]4 by picosecond and nanosecond laser pulses. The optical limiting response is measured by a transmission technique and the nonlinear absorption by a Z-scan technique. The experimental data are theoretically fitted, the mechanism for the optical nonlinearities and the optical limiting properties is discussed, and the absorption cross sections of the ground states and the excited states are evaluated by a rate equation model.

Stigmatic grazing-incidence flat-field grating spectrograph

A stigmatic grazing-incidence flat-field grating spectrograph was developed. The spectrograph consisted of a variable line-spacing concave grating and a grazing-incidence collecting optics composed of a cylindrical mirror and a spherical mirror. Using this spectrograph, we have obtained soft x-ray spectra of line-focused laser plasmas with good spatial resolution along the normal of the target surface over the entire wavelength range covered by the spectrograph.

Evolution of spectrally discriminated spatial uniformity of line‐shaped plasmas

A space‐resolved soft x‐ray (SXR) transmission grating spectrometer and a SXR streak camera are used to investigate the evolution of spectrally discriminated spatial uniformity of line‐shaped plasmas produced by uniform laser illumination in line focus. It is found that the spatial nonuniformity of SXR emissions and ion turbulence occur during optical laser’s heating. Various instabilities can be excited due to the long scale length in line‐shaped plasmas to produce the phenomenon.

A simple in situ calibration technique for soft x‐ray film

A simple valid in situ relative intensity calibration technique for soft x‐ray film is described. This is based on film exposure measurements of the uniform line‐shaped distributed soft x‐ray monochromatic irradiation transmitted through a step‐wedge absorption filter. Fitting the calibration data with Henke’s semiempirical equation for thick‐emulsion film, the characteristic curves for Shanghai 5F soft x‐ray film without supercoat (SIOM‐5FW) have been obtained in the wavelength region from 50 to 80 A.

Effect of an electron plasma wave on the propagation of an ultrashort laser pulse

The frequency shift and the pulse compression of an ultrashort laser pulse propagating in a background plasma wave are unified in the concept of phase modulation of the laser pulse by the plasma wave. An equation for the evolution of the pulse width is obtained, which is analogous to the energy-conservation equation for a classical particle moving in a potential well. The threshold amplitude of the plasma wave for pulse compression is estimated. Numerical calculations are presented to confirm these results. Laser pulse compression by a plasma wave should be feasible.

Space‐ and time‐resolved investigation of short wavelength x‐ray laser in Li‐like Ca ions

We have demonstrated the soft x‐ray amplification for lithium‐like Ca17+ 4f‐3d transition at 57.7 A with 900 ps, 1.05 μm drive laser pulse. The spatial distribution of the gain coefficient and temporal history of the lasing line emissions were also obtained.

Soft X-ray amplification by Li-like Al10+ and Si11+ ions in recombining plasmas

Experimental studies of soft X-ray lasers were carried out on the six-beam laser facility and the LF 12 laser facility of SIOM. Using a home-made one-dimensional spatially resolved grazing incidence grating spectrograph, XUV amplification has been observed in Li-like aluminum and silicon ions, by irradiation of slab targets with a line-focused laser. Based on time-integrated measurement, gain coefficients are 3.1 cm−1 for the 105.7 Å 5f−3d transition in Li-like Al ions, and 1.5 cm−1 and 1.4 cm−1 for the 88.9 Å 5f−3d and the 87.3 Å 5d−3p transitions in Li-like Si ions, respectively. The maximum gain × length products (GL) are about 2.5.