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We investigate the behaviour of an atom–cavity system via an adiabatic passage technique using a three-level ladder atom both for one-mode and for two-mode cavity QED. For one-mode cavity QED, we find that a single-photon Fock state can be generated via the technique of stimulated Raman adiabatic passage in the microwave domain. For two-mode cavity QED, we find that a two-photon pair can be generated via the technique of Stark shift rapid adiabatic passage (SRAP). We also find, for the two-mode cavity QED system, that an entangled state of the two modes in a microwave cavity can be prepared via the SRAP technique, in which the number of steps required is significantly reduced due to the adiabatic passage of the ladder atom–cavity coupled system.

We show that it is possible to achieve population inversion and upconversion lasing when a strong coherent field induces an exchange in the relative position of one dynamical Stark sublevel and a neighbouring level. This prediction is based on the fact that the dynamical level crossing results in a change in the direction of spontaneous emission. This provides a potential way towards short-wavelength laser generation.

We present phase control of the fluctuation-induced bistability in the three-level Λ-type system where a weak, amplitude-fluctuating component and a strong coherent component are used as a control field. With the addition of the stochastic component, optical bistability can be produced even if detunings of the probe and control fields from corresponding atomic transition frequencies are equal; without the addition, the medium is transparent to the input light. Depending on the relative phase between the stochastic and coherent parts, bistability appears or disappears and the threshold intensity is raised or lowered.

The photon statistics of the two-photon fluorescence of a two-level atom in a squeezed vacuum is investigated by using the second-order correlation function g (2) ( t ). Based on its analytical sol...

The nondegenerate two-photon interaction of a two-level atom with a broadband multimode squeezed vacuum is investigated. We find that in the two-photon process the squeezed vacuum has a driving effect on the atom which can lead to an ac Stark effect when the average photon number of the squeezed vacuum is larger than a critical value.

The fact that electrons are accelerated by intense laser pulses in a vacuum is particularly apparent from recently published work, but up to now no high-beam-quality laser vacuum acceleration scheme has been presented. In this paper, numerical simulations demonstrate that free electrons can be accelerated axially (high beam quality) in a vacuum by using two intersecting ultrashort, high-intensity laser pulses. As the maximum intensities are on the laser axes, a hollow channel is formed between the two laser beams. The electrons will be expelled by the transverse ponderomotive force of each beam to the axis of the symmetry, and can be trapped inside the channel until they are accelerated to relativistic energies. This makes possible axial rather than radial acceleration.

It is shown that, in an open ladder-type atomic system with spontaneously generated coherence (SGC), regardless of the existence of an incoherent pumping, a lasing without inversion (LWI) gain is always remarkable larger than in the system without SGC, by adjusting the strength of SGC. Moreover, LWI gain in the system without incoherent pumping is much larger than that with incoherent pumping, within some strength of SGC; while in the corresponding closed system with SGC, we can't obtain LWI gain at any strength of SGC, if no incoherent pumping is applied.

A new fluctuation phenomenon is observed through Langmuir probe measurements at the edge plasma in the KT-5C tokamak by applying a -90 degrees phase shift feedback. Using a two point correlation technique, it is found that this fluctuation mode has a longer poloidal wavelength and a definite frequency when compared with the usual edge turbulence. It is also found through bispectral analysis that this mode is a spontaneously excited quasi-coherent mode, which has almost no contribution to the cross-field particle flux

We investigate, using a nonlinear theory of laser physics, for a simple three-level atomic system the steady-state intensity behavior due to the effects of quantum coherence and decoherence. We find that a change from a noninversion laser to an inversion laser action can occur as the Rabi frequency of the driving field increases. The steady-state intensity of the laser field can arrive at a maximal value for a certain Rabi frequency of the driving field. We also find that the linear gain and the laser intensity tend to decrease for the linewidth of the driving field.

It is found on KT-5C tokamak that an edge fluctuation mode can be excited by using a pair of floating Langmuir probes. This mode is propagating along the magnetic field with its amplitude decreasing drastically when it is off the magnetic field line. Preliminary feedback experiments show that the broadband edge turbulence can be reduced or enhanced depending upon the phase shift of the feedback network.

For atoms of three-state ladder or V configuration, a large population may be 'locked' into a single high-lying excited state via atomic lower-state coherence even when it exceeds the total population in the two lower states. The conditions are analysed and the two systems are compared.

The interaction of a pair of coupling two-level atoms with a radiation field is studied. The effects of a dispersion force (dipole-dipole interaction) on the emission spectrum are analysed. It is found that the dipole-dipole interaction induces an asymmetry of the emission spectrum, which is most obvious in a vacuum field.

The ionization behavior of linear polyatomic molecular ions in ultrashort, intense laser fields was investigated with the time-dependent Schrodinger equation solved by the standard split-operator algorithm. The enhanced ionization effect was found as a general feature in the ions when the internuclear separation was in a critical distance range and can be explained in terms of the field-induced over-barrier ionization mechanism. In addition, the ionization energy does not influence the ionization probability significantly.

In recent years it has been shown that atomic coherence or interference of pathways can be established through incoherent processes. We have investigated the generation of optical bistability via interference of incoherent pump processes, which is a new incoherent method leading to atomic coherence. The standard model of optical bistability with an atomic sample is considered.

We propose a scheme to generate the entangled state of two Lambda-type three-level atoms trapped in distant cavities by using interference of polarized photons. Two possible spontaneous emission channels of each excited atom result in a coherent superposition of the states of two atoms. The subsequent detection of the different polarized photons reveals that both atoms are in different ground states, but an interference effect prevents us from distinguishing which atom is in which ground state; the atoms are thus entangled. In comparison with the original proposal of interference-induced entanglement [C. Cabrillo, J. Cirac, P. Garcia-Fernandez, and P. Zoller, Phys. Rev. A 59, 1025 (1999)]], in our scheme the weakly driven condition is not required, and the influence of atomic excitement and atomic recoil on the entanglement fidelity can be eliminated.

A noninversion laser system which is closed lifetime broadened and free of the restriction on atomic decay rates is proposed. For the realization of lasing without inversion, the Rabi frequency of the applied field must exceed a lower threshold. Moreover, the coherence term in dressed states must enhance the gain. These results are obtained beyond the specific approximations

In this paper, the spectral, temporal and spatial properties of few cycle optical pulsed beam on propagation in free space has been studied. We analyze the spectral shifts of the ultrashort pulse in the far zone, and then discuss the scaling law of the pulsed sources. It is found that by the truncation of the pulsed beam, the scaling law may be destroyed. In this case the spectral shifts on propagation of the few cycle pulses may be observed in experiment. On the other hand, we reveal an analytical form of the pulsed Gaussian beam in free space and analyze the space-time coupling on propagation.

Two possible designs are considered in this paper for increasing the GL value of recombining X‐ray lasers. A ‘‘fibers target’’ structure was proposed to get a rapid 3‐dimensional adiabatic expanding at the initial state followed by a slower 2‐dimensional plasma expansion. A ‘‘hybrid model’’ was used to calculate the plasma behavior of the target and the results are presented. Theoretical results about X‐ray pumped recombination X‐ray laser are also reported.

A numerical method based on techniques of inverse Fourier convolution and nonlinear least square algorithm, etc., is presented for obtaining high‐resolved X‐ray spectra of laser plasmas, which can eliminate the line‐broadening induced by radiation sources and spectrographs, and can improve the spectral resolving power of spectrographs. The code ESDAP has now been successfully applied to the analysis of spectra from line‐shaped Mg and CaF2 laser plasmas.

The influence of focus spot and target thickness on multi-keV x-ray sources generated by 2ns duration laser heated solid targets are investigated on the Shenguang II laser facility. In the case of thick-foil targets, the experimental data and theoretical analysis show that the emission volume of the x-ray sources is sensitive to the laser focus spot and proportional to the 3 power of the focus spot size. The steady x-ray flux is proportional to the 5∕3 power of the focus spot size of the given laser beam in our experimental condition. In the case of thin-foil targets, experimental data show that there is an optimal foil thickness corresponding to the given laser parameters. With the given laser beam, the optimal thin-foil thickness is proportional to the −2∕3 power of the focus spot size, and the optimal x-ray energy of thin foil is independent of focus spot size.

It is shown that the large amplitude Langmuir wave driven by two collinear laser beams with a frequency difference approximately equal to the plasma frequency exhibits bistability and hysteresis. The threshold pump intensity for the occurrence of the bistability is rather low compared to most laser‐plasma experiments. By using the hysteretic effect, relatively weak pump intensities can result in a very large amplitude of the Langmuir wave.

In this paper, the authors consider a more realistic case of linear density profile for laser-irradiated plasma, and obtain the field structure over the whole coronal region by directly solving the wave equation with numerical method. The dependence of the field structure on the wavelength of incident Laser light, the initial scale length of the density profile and the magnitude of the magnetic field is studied. In addition, the resonant absorption is also discussed for the above cases. The results are in good agreement with those obtained by computer simulations.

Above-threshold ionisation (ATI) with a Gaussian laser pulse is studied using an essential states approach. The authors show that the temporal shape of the laser pulse must be taken into account in investigating the time-dependent behaviour of ATI continua.

In line-focused laser-produced plasma experiments on planar and cylindrical targets, we have observed the line-focused laser beam breakup into filaments as well as small-scale plasma jet-like structures. These phenomena might become obstacles in achieving optimum X-ray lasing in the type of experiments using line-focused laser-produced plasmas as a gain medium.

This paper presents the detailed studies of the focusing of pump beams and the excited electron plasma waves(EPW) in a PBWA(Pasma—Beat—Wave—Accelerator) by beating two self-trapped laser beams. The equations governing the saturated amplitude of EPW in nonuniform pump beams have been derived analytically. With these the condition for self-trapping of pump beams has been studied self-consistently. The optimum frequency mismatch parameter and the corresponding optimum initial plasma density as well as the maximum amplitude of the EPW have been obtained analytically. The transverse distributions of the EPW for Gaussian pump profile have been calculated numerically and show peculiar characteristics for certain frequency mismatch parameters. In addition, the effect of the radial component of the EPW on the bunch of accelerated particles in PBWA has been briefly discussed.

A mechanism driving filamentation instability by self-generated small-scale magnetic fields in laser-produced plasmas is suggested with use of a simplified model. The wavelength dependence of the filamentation mechanism is very strong. The predictions of the model are consistent with experimental observations.

In line-focused laser-produced plasma experiments, we have observed large-scale plasma jets. These plasma jets are in appearance similar to “tips of ox horns”, and always appear at the boundaries between the hot plasmas and the cold target materials, or between two plasmas with different Z-numbers.