The nonlinear propagation of intense electromagnetic waves in weakly-ionized plasmas is considered. Stimulated scattering mechanisms involving electromagnetic and acoustic waves in an unmagnetized plasma are investigated. The growth rate and threshold for three-wave decay interactions as well as modulational and filamentation instabilities are presented. Furthermore, the electromagnetic wave modulation theory is generalized for weakly ionized collisional magnetoplasmas. Here, the radiation envelope is generally governed by a nonlinear Schrodinger equation. Accounting for the dependence of the attachment frequency on the radiation intensity, ponderomotive force, as well as the differential Joule heating nonlinearity, we derive the equations for the nonthermal electron density and temperature perturbations. The various nonlinear terms in the electron motion are compared. The problems of self- focusing and wave localization are discussed. The relevance of our investigation to ionospheric modification by powerful electromagnetic waves is pointed out.

The simultaneous dynamics of self-focusing and stimulated Brillouin back scattering (SBBS) is investigated. It is shown that scattered radiation appears as the high intensity periodical bursts by nonstationary self-focusing of incident beam. However, the time averaged level of scattered radiation is quite low. The important feature of the reviled self-adjustment SBBS regime is a weak dependence of the time averaged reflection coefficient as on pump wave intensity so as on spontaneous level of reflected wave that is in accordance with many laser-plasma experiments.

The interaction of high-power femtosecond laser pulses with matter has now become an important field of study, as the advent of high-power short-pulse laser systems offers the chance of studying a completely new and very complex regime of laser plasma generation. In this paper the results on conversion efficiency into X-ray are presented for a broad range of experimental parameters. The situation is studied, when the contrast of laser pulse is sufficiently high, i.e. the prepulse is eliminated. The results are then compared with the experimental data. We pay the main attenuation on the regime of normal skin-effect in contrary of our previous report.

The reflection of radiation pulse from oncoming ionization fronts is studied using two approaches, the resulting reflection coefficient is well above the previous prediction. We show that upon reflection from an ionization front with optimum density, the upshifted frequency of radiation pulse can exceed twice the drive frequency and the reflected energy exceed the incident energy. The extra energy required for pulse amplification can be supplied by the ionizing driver.

It is demonstrated that in an underdense plasma the process of three-dimensional evolution of the short and strong laser pulse with duration about several plasma periods leads to the compression and self-modulation of the pulse, so that during a fairly long period of time the beats of pulse amplitude generate resonantly a strong and stable plasma wakefield. The intensity of the wake-field is so high that it can provide a new promising outlook for the plasma based accelerator concept.

Variational approach is adopted to study the evolution of an ultrashort laser pulse copropagating with an electron plasma wave. By use of the potential well description, the conditions for pulse compression, decompression or stationary state are found, which are results of the competitions between the dispersive diffusion and phase modulation of the pulse by the plasma wave. Results are compared with the numerical calculations of the evolution equation to prove the applicability of the above approximate method.

The modulational instability of intense electromagnetic waves has been investigated by incorporating the ponderomotive force as well as inverse-bremsstrahlung heating. It is found that a reduced thermal conductivity can significantly enhance (reduce) the growth rate (threshold) of the modulational instabilities.

The nonlinear generation of second harmonic electromagnetic wave from a thin inhomogeneous (dense and rarefied) plasma layer (of width d) by obliquely and normal incidence of light wave is analyzed. We consider the effect of external time-dependent magnetic field on the generation and amplification of waves. Two cases are considered; when the external magnetic field oscillates at frequency (i) equal, and (ii) double the frequency of the incident wave.

The expressions for the threshold intensity and amplification coefficient, in practical units, of the convective two-plasmon decay instability in a laser-produced plasma are obtained using the fluid theory and accounting for the plasmon collisional damping. Analyses of these expressions show that the plasmon collisional damping significantly increases the threshold for excitation of the instability and reduces the amplification coefficient as well as the excited spectrum of the plasmons substantially for electron temperatures smaller than 1 keV.

Laser plasma interactions, plasma's hydrodynamics, and x-ray emissions in half-cylindrical target have been studied. It is found that this kind of target geometry can converge plasma expanding along the radial direction and form uniform flat distributions of electron density. Based on the unique characteristics of this kind of target, we suggest it be used for x-ray laser research. We also suggest a new configuration of two laser heating for x-ray lasers.

The model describing asymmetrical compression of high-aspect-ratio laser-fusion shells under conditions of non-uniform illumination is proposed. Thin-shell approximation is used as a base. Motion equations of a thin shell are solved numerically by code 'SOM'. The asymmetry being brought during acceleration phase is characterized by asymmetry function introduced taking into account thermal conduction smoothing of energy deposition in corona, and is set as initial conditions. Analytic solution of small three-dimensional perturbations growth problem is derived. It gives a good estimation of compression losses even for large amplitude and for several modes superposition case. The analysis of experiments conducted on the SOKOL, OCTAL, OMEGA facilities is given. The model represents a good agreement with experimental data: degradation of DT-fuel compression and neutron yield falling can be explained by large scale asymmetry appearance due to target illumination non-uniformity.

We first report measurement of air laser impulse coupling coefficients as large as 15 dyn/W, obtain with ns-duration 0.53 micrometers (double frequency) laser pulses incident on Al-targets, and compare with that of 1.06 micrometers laser.

In this paper, we present a theoretical model which treats one-dimensional target heating and vaporization as well as energy absorption and collision reactions in the melting metal vapor. The coupling effects have been calculated for 0.308-micrometers XeCl laser radiation to aluminum. The incident laser intensity and the pulsed duration are 10⁷ - 10⁹ W/cm² and 80-ns respectively. The time relations of thermal and impulse coupling coefficients are obtained by solving non-linear heat conduction and rate equations about the temperature and density. These results are compared with the experiment measurements and the agreement is fairly good.

In this paper, the results of the X-ray laser gain experiments of Li-like K and Ca ions, conducted recently at LF12 Laser Facility of SIOFM with KCl and CaF₂ slab targets, will be presented. Also presented will be the space-resolved time history of ASE emission in the Li-like X-ray lasers and the in-situ calibration for the X-ray film used in the experiments.

Numerical modeling has been used to investigate the performance of O VIII x-ray recombination lasers driven by picosecond laser pulses (2 ps) of wavelength 1.053 micron.. The results show that high gain length product in O VIII x-ray recombination laser is possible by irradiating targets with the CPA beam of the glass laser facility Vulcan.

For the X-ray laser researching toward shorter wave length, we set up compact short pulse laser facility with high intensive output at the variable pulsewidth from 20 ps to 2.5 ns. Occupying a table smaller than 10 m² and with output of 2.5 J in 20 ps this facility is reported with the emphasis on the use of X-ray lasers research and laser-plasma study.

A new x-ray laser scheme is proposed that lases on Balmer (beta) transitions from 2.87 nm to 5.99 nm in H-like ions and is resonantly photopumped by Ly (gamma) radiation from the same kind of H-like ions. Optimization designing for targets and driving laser conditions is carried out using simulation codes. A recombining plasma produced from a slab target irradiated by a 50 ps drive pulse is found to be the ideal pump plasma to provide maximum Ly (gamma) line radiation. Numerical calculations predict that the high gain coefficients on Balmer (beta) transitions of H-like ions with atomic number Z equals 9 to 13 can potentially be achieved with this scheme.

A theoretical model and corresponding computer code HELM developed to calculate line profiles from high-Z emitters of H, He, Li isosequences in hot plasmas are described. Line profile calculation involves quasi-static ion broadening, impact electron broadening, natural and Doppler broadening. Line profiles are calculated for the n equals 5 to n equals 3 transitions of Li-like AlXI and CaXVIII ions as applied to the conditions of recombination X-ray laser experiments and for the n equals 5 to n equals 4 transitions of Li-like GeXXX ion for theoretical investigation of the laboratory X-ray laser scheme with recombination radiation photopumping. The results of comparison between the experimental data for the linewidth of the 5F-3D AlXI line and calculated values at two different plasma temperatures are analyzed in detail.

Program for the levels kinetics calculations of a multi-charged ions in plasma is presented. It is based on the spectroscopic data base about bound ionic states which enables to investigate different laboratory X-ray laser schemes. The gains calculations are illustrated by examples for the transitions of Li-like Al and Ge under conditions of recombination pumping and broadband photopumping.

The spatial distributions of lithiumlike SiXII ion and sodiumlike CuXIX ion recombination X- ray lasing gains are presented in this paper. It shows that the recombination X-ray lasing gain region is at hundreds of micrometers from the target surface and the electron density in the gain region is about 10¹⁹ cm^-3 while there exists absorption near the target surface with higher electron density (> 10²⁰ cm^-3).

By the calculation of the 4f-3d line gains of Li-like Ca ions, which varied with electronic densities, temperatures and abundances, we found the plasma conditions on which the 4f-3d gain could be produced. Then, we calculated the gains which varied with time and space, under the plasma parameters which were calculated with self-similar model in cylindrical geometry.

Examples of experiments using x rays from laser produced plasmas are given.

With the help of the transmission grating spectrometer (PTGS), we have obtained the real emission spectra of several elements. The band structures of the soft x-ray spectra from laser produced plasmas are extensively studied as the function of atomic number and laser intensity. Finally, the PTGS space-resolved spectra from the laser heated half-cylindrically grooved target show that this kind of semi-closed geometry is a promising candidate for x-ray laser targets.

The systematic ablation plasma study with the measurement of ion emission in laser-target interaction is presented. We have obtained the scaling laws of ablation parameters with laser intensities for aluminum plasmas in the intensity range of 10¹¹ - 10¹³ W/cm², under both of the line-focused and the spot-focused laser irradiation.

The detailed level to level partial dielectronic recombination rate coefficients of Li-like Si ion through 2 pnl manfolds are calculated. These rate coefficients are presented by the average wavelength (lambda) and average absorption oscillator strengths f defined by P. L. Hagelstein. All calculations are made on the basis of Cowan's program (HFR).

The ion cyclotron maser instability has never been considered in the literature. It is demonstrated that in the case of the ion cyclotron maser instability the relativistic mass effect of very low velocities on the ion-wave cyclotron resonance conditions plays an exceedingly interesting role. The ion cyclotron maser instability can actually exist in a loss-cone plasma in certain physical conditions.

A brief survey of the relativistic BBGJY hierarchy for an electromagnetic system and its main applications are given.

Progresses of anomalous nuclear phenomenon studies are reviewed. The anomalous neutron emission from a glow discharge tube with flowing deuterium gas is addressed. Theoretical explanation based on the concepts of 'Combined Resonance Tunneling' and 'Semi-Resonance' is presented. It is suggested to use laser-plasma interaction for testing the model.

A new type of cavity, a distributed feedback cavity from periodically rippled walls is developed. The Raman free electron laser (400 KeV/800 A) with the new cavity is studied. The spectral measurements using a microwave grating spectrometer are presented. The frequency selection, narrowed spectral bandwidth with central wavelength at 8 mm, and output power enhancement show that oscillation happened.

In this paper, the FEL of cylindrical waveguide loaded with dielectric is studied by using fluid theory. It is shown that the main mode of super-radiation in this system is TE mode. It has all characters of slow-wave FELs.

We present the preliminary results of our ray-tracing program for soft X-ray optical system simulation. The simulation has been made for the toroidal mirror used in X-ray laser diagnostics as a relay optics. We investigated systematically the energy transportation characteristics and the space-resolving ability of toroidal mirror, especially the influence of both defocusing and changing of collecting solid angle. The results confirmed that the energy transportation of toroidal mirror is linear, the space-resolving ability is good enough.

It is shown that the ladder system with lower-level coherence may be used to obtain lasing without inversion. The present model system has several important features. (1) No requirement is placed on atomic decay rates. (2) The Rabi frequency of coherence-driving field must exceed a lower threshold. (3) An unidirectional pumping is indispensable. (4) A dressed-state-coherence origin of gain is proved without strong coherence-driving field approximation.

In this paper, the optical metric model is introduced on the study of light-matter interactions and the corresponding discussions are given.

Applying the self-consistent density distributions and ponderomotive potential of one dimensional isothermal expanding laser-plasma, the optical metric of high power laser plasma is derived and the physical significance of which is presented.

A quasi-periodic design method for soft x-ray multilayer reflector to achieve high reflectivity and low loss is presented. The dependence of the reflectivity on the optical constants of the absorbing layers for a given substrate and spacer materials is investigated, and the criterion of choosing optical components is also discussed. We find that when the extinction coefficient of the absorber is large, the reflectivity of the multilayer reflector is governed by the difference of the extinction coefficients of the components. In order to obtain high reflectivity in the case of large extinction coefficient, one should choose a pair of materials with large difference of extinction coefficients.

The optical properties of a cantor-like metal-insulator superlattice for both p-polarized and s- polarized wave are studied by employing the transfer matrix formalism. Based on the hydrodynamic theory and taking account of retardation effect, we have calculated the dispersion relations of the electromagnetic modes of the superlattices. The results show that the dispersion relations of the modes have rich multi-fractal structure, and the frequency gaps, in which there are strong reflective peaks, appear strikingly in the region of the extreme ultraviolet and soft x-ray. Around the fixed points, the patterns of the bands are scale invariant.

The small scale density fluctuations in the interior of HT-6M Ohmic plasma have been studied by CO₂ laser collective scattering system in deuterium discharges covering a wide range of nq_a (chord-average density times safety factor at the limiter) and energy confinement time. The relative density fluctuation level in the interior is inversely proportional to the toroidal magnetic field and average density, and the energy confinement time (tau) _E decreases with the fluctuation level increasing in the region where (tau) _E linearly increases with nq^0.5_a and satisfies the Goldston scaling law. It is suggested that the microturbulence in the interior zone is responsible for anomalous transport in tokamaks.

Recent advances in short-pulse high-brightness lasers, capable of delivering focused irradiances far in excess of an atomic unit, have opened up an entirely new field in experimental research. Theoretical predictions and new phenomena of super-intense laser- matter processes can now be examined in the laboratory. An experiment on a search for multiphoton-induced inner-shell excitations is briefly described. Possibilities of conducting several fundamental experiments in quantum electrodynamics and nuclear physics are individually discussed.