We theoretically and experimentally investigate the conditions of obtaining a narrowband flat-top Brillouin gain spectrum (BGS) based on single-frequency and multi-frequency phase modulations. Using the unequal-amplitude spectral lines, the flat-top BGS can be realized by controlling the intensity ratio and the frequency separation between them. In experiment, we obtain the flat-top gain spectra with the bandwidths of 40 MHz and 125 MHz, and with the top fluctuation of less than 0.21 dB. Based on this, we also achieve low distortion Brillouin amplification of a probe signal pulse and spectrum.

An injection-locking excimer laser beam with a pulse duration of 25 ns is focused on the surface of a polymide film. The laser beam that passes through the etching film is shorter than the original one. By optimizing the thickness of the film and the beam powerdensity, a pulse with a 3-ns pulse duration can be obtained using this switch technology.

Time and space-resolved emission spectroscopy measurements were performed to investigate plasma dynamics during laser evaporation of a graphite target in an ambient inert atmosphere. Intense molecular emission is found to occur behind a front separating the plasma from the foreign gas. Two stages of expansion are found and are well described, using a viscous drag force model for the first one and a delayed ideal blast wave model for the second. The vibrational temperature estimated using the Swan band in helium at different pressures is presented.

All of mankind, not only the readers of this Journal, is now fascinated by the laser. The process of many preceding physics discoveries beginning with Einstein (Zürich lecture, printed 1916, see A. Held, General Relativity and Gravitation One Hundred Years after the Birth of Einstein, Plenum, New York, 1980, Vol. 1, p. 17–21) and how this earth shattering discovery was not recognized by the giants in science is really a process of “how it happened” and the fact is: Charles Townes is its creator. Since there were some dark clouds through which this discovery of our century (next to the quantum theory and the theory of relativity) had to finally shine through, it is a revelation to now read what its creator has to say; modest, quiet, but true and fascinating.

A review of structural materials choices under irradiation in fusion environments is presented. Results on the neutron source term and the intensities in the structural materials as a function of pulse time, energy, and protection is given. The role of multiscale modeling for understanding the basic physics in irradiated materials is explained, and simulations of metals under pulse irradiation and SiC are reported.

The problem of initial thermal velocity and the space charge effect of electron guns in numerical simulations have been investigated deeply. In general, the current software can meet the engineering requirements. However, the electron's initial thermal velocity and the space charge effect lack sufficient consideration. The above two factors significantly limit the performances of electron guns. Moreover, the parameters of electron guns are approximated based on a limited number of electron trajectories. Thus, the statistical distribution of the beam electron resulting from its initial thermal velocity is not considered adequately in present software. This paper introduces the equivalent meridional projected trajectory equation and the curvilinear axis evolution theory of the current density of toroidal electron sub-beam, and subsequently the current and charge density distributions in electron guns can be derived through iteration calculation. Based upon, the virtual crossover of an electron gun is determined by its current density distribution. As well as, a relevant numerical algorithm is developed and the related program is modified based on the popular commercial software SOURCE. Tungsten cathode guns, LaB6 cathode guns, field mission guns and Pierce guns are simulated respectively by examples. The calculations prove that the modified software is effective and practical.

The goal of the experiments on “Module A-5” and S-300 machines for some 15 years was to study the “liner-converter” inertial confinement fusion (ICF) scheme. A new class of fast instabilities of z pinches was studied both in experiments and in analytical theory. Stabilization of the light liner has been achieved by means of an extrinsic magnetic field. Formation of thin overheated current-carrying shells has been predicted analytically and seems to be really observed. Both theory and simulations predict growing Te and heat flux onto the converter by using heterogeneous z pinches with spatially separated regions of efficient energy exchange and of efficient heat conductivity. In our first experiments of this kind, impurities were inserted by means of placing thin glass fibers into a He jet. Growing intensity of the spectral lines of He-like chlorine from the cathode surface confirms the growth of heat flux. Theoretical investigations and 2.5-D simulations were devoted to some basic points of this program.

We generate self-phase-stabilized pulses by difference-frequency generation of a hollow-fibre broadened supercontinuum followed by two-stage optical parametric amplification. This system allows the production of broadband pulses widely tuneable in the near-IR wavelength region. Energies up to 0.2 mJ with 15 fs pulse width are demonstrated. These characteristics make this source suitable as a driver for attosecond pulse generation.

We examine the electron acceleration induced by an ultra-relativistic intensity laser–plasma interaction in a two-dimensional plasma channel in the presence of a self-generated transverse magnetic field. We find that the electron dynamics is strongly affected by the laser pulse polarization angle, plasma density, and magnetic field strength. We investigate in detail, the dependencies of the electron acceleration in terms of different parameters and find excellent agreement with non-magnetized plasma in the absence of the magnetic field. The numerical results show that the self-generated magnetic field plays a constructive role in the electron acceleration process. It is shown that electron acceleration is more affected by self-generated magnetic field for the laser radiations with large polarization angles. The numerical results show the maximum enhancement for electron acceleration for a laser radiation with polarization angle θ = π/2.

The bubble regime acceleration of electrons by a short pulse laser in a carbon nanotube (CNT) embedded plasma is investigated, employing two-dimensional Particle-in-Cell simulations. The laser converts the CNT placed on the laser axis into dense plasma and expels the electrons out, to form a co-moving positive charged sheet inside the bubble. The additional field generated due to sheet enhances the energy of the monoenergetic bunch by about 5% and their number by 5–20%. For a typical 40 fs, 7.5 × 1019 Wcm−2 pulse in an underdense plasma of density n0, CNT of thickness 25 nm and electron density 30n0, produces a monoenergetic bunch of 115 MeV with 5% energy spread. When CNT density is raised to 90n0, the energy gain, energy spread and accelerated charge increases further. The analytical framework supports these features.

The third-order nonlinear optical properties of three hydrazone derivatives, namely, ethyl 2-((2E)-2-(4-(dimethylamino)benzylidene]hydrazinyl)-5-nitrobenzoate, ethyl 2-((2E)-2-(4-chlorobenzylidene)hydrazino)-5-nitrobenzoate, and methyl 5-nitro-2-((2E)-2-(4-nitrobenzylidene)hydrazino)benzoate were investigated by the single beam Z-scan technique with nanosecond laser pulses at 532 nm. The compounds were doped into PMMA (poly (methyl methacrylate)), and their third-order nonlinearity was studied with a prospective of reaching a compromise between processability and high nonlinear optical behavior. The optical limiting study of the samples was carried out at 532 nm. The measured values of the third-order nonlinear susceptibility, χ(3), and the nonlinear refractive index, n2, are of the order of 10−13 esu and 10−11 esu, respectively. The nonlinear absorption in materials was attributed to reverse saturable absorption. The results are quite promising for possible applications in photonic devices.

In this paper, the opacity of plasma in local thermodynamic equilibrium condition was investigated numerically. The plasma was assumed to be produced by interaction of high power pulse laser with carbon and aluminum. Spectrally resolved opacities under different plasma temperature and density conditions were calculated and radiative absorption due to three absorption mechanisms; inverse bremsstrahlung, photo-ionization, and line absorption in plasmas was studied numerically. The purpose of this study is to calculate the values of absorption for inverse bremsstrahlung and photo-ionization processes for aluminum and carbon plasmas and to compare them for those of cold matter. In this investigation, the influences of density and temperature on plasma absorption were evaluated. The calculation results show that the opacity strength strongly depends on the plasma temperature and density.

A s-polarized short-pulse laser impinged obliquely on an overdense plasma slab is shown to produce very significant second harmonic in the direction of specular reflection and transmission. The laser induces a non-linear current on electrons, which is curl free. However, with sharp plasma boundary, it gives rise to electromagnetic radiation at the second harmonic. Our formalism includes multiple reflections of the incident and second-harmonic waves from both the front and rear surfaces. The present work includes finiteness of the slab. The normalized second-harmonic amplitude acquires a sharp peak at some specific angle of incidence for a particular set of parameters dependent on thickness of the slab and plasma density.

A paraxial ray formalism is developed to study the evolution of an on axis intensity spike on a Gaussian laser beam in a plasma dominated by relativistic and ponderomotive non-linearities. Ion motion is taken to be frozen. A single beam width parameter characterizes the evolution of the spike. The spike introduces two competing influences: diffraction divergence and self-convergence. The former grows with the reduction in spot size of the spike, while the latter depends on the gradient in non-linear permittivity. Parameter δ = (ωpr00/c) a00/(3.5 r00/r01) characterizes the relative importance of the two, where r01 and r00 are the spike and main beam radii, ωp is the plasma frequency, and a00 is the normalized laser amplitude. For δ > 1, the intensity ripple causes faster self-focusing of the beam; higher the ripple amplitude stronger the focusing. In the opposite limit, diffraction divergence increases more rapidly, slowing down the self-focusing of the beam. As the beam intensity rises due to self-focusing, it causes stronger generation of the third harmonic.

Recently, we have proposed an experiment to test the persistence of the polarization in a fusion process (D+D→3He+n), using a powerful laser hitting a polarized HD target. The purpose of the present contribution is to examine in more detail the experimental constraints, to move from a principle proposal to a doable experiment. Some of the difficulties are as follows: Production of a windowless cryogenic HD target and target cryostat vacuum breakdown, identification of thermal fusion or accelerated deuterons, inducing nuclear reactions, and finally, a clear signature of the polarization persistence of the fused deuterons must be found. Those points will be reviewed and discussed in the scope of the new results presented at this conference.

Effects of external static magnetic field (applied in $\hat y$-direction) on resonant excitation of surface plasma waves (SPW) have been investigated over the metal free space interface. The high power laser $({\rm \omega} _0,\;\vec k_{0z})$ is incident over the metal surface and exerts a ponderomotive force on the metal electrons in the skin layer. The ponderomotive force disturbs the quasi-neutrality of plasma which results into the excitation of space charge field at the frequency 2ω0. The electron density perturbation at frequency 2ω0 driven by self-consistent space charge potential couples with the oscillatory velocity due to the seed SPW $({\rm \omega}, \;\vec k_z)$ and produces nonlinear current to drive another counter propagating SPW $({\rm \omega} _1,\;\vec k_{1z})$ at the phase matching conditions of frequency ω = ω1 − 2ω0 and wavenumber $\vec k_z = \vec k_{1z} - 2\vec k{}_{0z}$ (by feedback mechanism). The parametric process becomes resonant at 2ω0 ≈ ωp and the maximum growth rate is achieved for an incidence angle of laser θ = 40°. The growth rate of the process reduces to half on increasing the magnetic field from 0.49 to 2.45 MG. The present study may be significant to the laser absorption experiments where surface rippling can strongly affect the laser energy absorption.

A conical-pinched electron-beam diode has been studied with the objective of increasing the brightness of this inherently high current ion beam. Experiments and calculations are described that suggest it may be possible to obtain powers as high as 1013W/cm2 at 4MV from a carefully designed insulated-anode-type pinched-electron beam diode.

New experimental results of investigations of the interactions of an intense 4.3-GeV electron beam with an aligned single crystal are given in the case when the electrons travel close to the crystalline planes (110). The growth of low energy radiation yields with the intensity of the electron beam and the peculiar properties of the produced γ-quanta at their passage through a small collimator aperture were observed. Large angular asymmetry at the scattering of low energy γ-quanta, which is evidence of high polarization of the radiation, was also detected. These unexpected phenomena may be stimulated by strong correlations of atomic excitations in crystals. The obtained results will be of use for understanding of the properties of both the excited crystalline medium and the mechanism of intense radiation under these conditions and also for practical applications of the radiation.