Lasing near 200 Å with neon-like zinc and lithium-like sulfur

In this paper we present the recent results obtained on X-ray lasers with the new facility of LULI (Palaiseau, France). As regards the study of collisional-excitation pumping we show that the J=0–1 line of neon-like zinc, at 212 Å, exhibits a surprisingly large gain coefficient of 4.9 cm^–1. A detailed comparison of the time-dependent intensities of the J=0–1 and the J=2–1 line at 267 Å leads to the conclusion that these two lines are not emitted in the same region of the plasma. On the other hand we performed a theoretical and experimental study of 5g-4f lasing line of lithium-like sulphur at 206.5 Å. For the first time, in the case of plasma recombination pumping, we did not observe any reduction of the gain coefficient when the plasma length is raised from 1 cm to 2 cm. From numerical simulation this is likely due to radiation trapping and similar processes having much less influence on 5g-4f population inversion than on previously observed lithium-like lasing transitions. These results show that large gain-length values should be obtained with 0.5 kJ driving laser pulses.     

Few-cycle relativistic solitons in plasmas

A set of exact one-dimensional solutions to coupled nonlinear equations describing the propagation of a relativistic ultrashort circularly polarized laser pulse in a cold collisionless and bounded plasma where electrons have an initial velocity in the laser propagating direction is presented. The solutions investigated here are in the form of quickly moving envelop solitons at a propagation velocity comparable to the light speed. The features of solitons in both underdense and overdense plasmas with electrons having different given initial velocities in the laser propagating direction are described. It is found that the amplitude of solitons is larger and soliton width shorter in plasmas where electrons have a larger initial velocity. In overdense plasmas, soliton duration is shorter, the amplitude higher than that in underdense plasmas where electrons have the same initial velocity.     

Pressure broadening of methane lines in the 6190Åand 6825Åbands at room and low temperatures

Measurements of pressure broadened half-widths have been performed for one vibration-rotation line in the 6190Åmethane band and one vibration-rotation line in the 6825Åmethane band. Self-, nitrogen-, hydrogen- and helium-broadening have been measured over a temperature range of 77–295 K. Pressure broadening coefficients and temperature dependence indices have been obtained for each line and broadening gas.     

Ti-pumped Mo X-ray laser at 24 Å

We propose using the Ti XXI He- emission line to resonantly photo-pump Li-like Mo (Z=42) and produce lasing on several n=5 n=4 transitions near 24 Å. The continuum emission from Ti photoionizes the Mo to the Li-like isoelectronic sequence. Gains of 1–2 cm^–1 are calculated on these lines before the inclusion of Stark broadening which lowers the gain by as much as a factor of two.     

First observation of lasing at 231 Å in neon-like nickel using the prepulse technique

We report lasing for the first time in nickel on the neon-like J=01, 3p3s transition at 231 Å as well as several weaker transitions including the J=2»1 lines at 298 Å and 304 Å. Amplification is seen only when the prepulse technique of using a low intensity prepulse before the main optical drive pulse is used to illuminate the nickel target. The prepulse technique is also shown to produce lasing in copper and dramatically improve the output of the germanium laser.     

Clustering of silver atoms in hydrogenated silver–sodium exchanged glasses

The diffusional growth regime of silver clusters in hydrogenated silver–sodium exchanged glasses has been numerically analysed. The diffusion coefficients of the three elements that contribute to silver cluster formation, namely H, Ag⁺, and Ag⁰, have been established. The activation energy of the reactant Ag⁰ diffusion coefficient is consistent in the three analysed different experimental results: Ag loss through evaporation, near-surface Ag accumulation, and optical absorption density. The calculated Ag⁰ diffusion coefficient accounts for the threshold time necessary to obtain a cluster size to give rise to a detectable absorption. Received: 27 September 1999 / Accepted: 11 October 1999 / Published online: 8 March 2000     

Tunable Fano resonances in silver–silica–silver multilayer nanoshells

We study the plasmonic properties of silver–silica–silver multilayer nanoshells using finite-difference time-domain methods. Silver is a weakly dissipating metal and is able to support higher order resonances compared to strongly dissipating metals like gold. We show that Fano resonances occur even in symmetric cases. Symmetry breaking via the introduction of core offset further enhances these Fano resonance peaks and leads to the appearance of higher order resonances. The optical properties of the multilayer nanoshells are explained using the plasmon hybridization theory and the results are compared to similar multilayer nanoshells with gold core and outer shell.     

A novel type of solitons in electron-ion plasmas

By using one-dimensional self-consistent relativistic fluid model, a novel type of moving relativistic electromagnetic solitons with high intensity in electron-ion plasmas where the ion dynamics is taken into account is investigated numerically. Unlike solitons with single-humped scalar potential found in previous studies, these solitons possess multi-humped scalar and vector potential. The existence of such soliton solutions is investigated in plasmas with different background densities, and the properties of these solitons are presented in detail. We found that the peculiar profile of electron density has alternating regions of humps and dips like a Bragg's grating.     

Compressible sub-Alfvénic MHD turbulence in low-beta plasmas

We present a model for compressible sub-Alfvénic isothermal magnetohydrodynamic (MHD) turbulence in low- beta plasmas and numerically test it. We separate MHD fluctuations into three distinct families: Alfvén, slow, and fast modes. We find that production of slow and fast modes by Alfvénic turbulence is suppressed. As a result, Alfvén modes in compressible regime exhibit scalings and anisotropy similar to those in incompressible regime. Slow modes passively mimic Alfvén modes. However, fast modes show isotropy and a scaling similar to acoustic turbulence.     

The polarized spectrum of benzene-d 6 single crystal at 2000 Å

The Roothaan open-shell LCAO-MO-SCF method was coupled with the Simons model potential in calculations of internuclear distances and ionization potentials for Li₃, Na₃, K₃, Rb₃, and Cs₃ taking core polarization into account.     

Polytropes in plasmas described by kappa distributions – Application in atmospheric modelling

The paper derives the complete formulations of polytropic behaviour for plasmas described by kappa distributions. This is achieved by employing both positive and negative types of phase-space kappa distributions of a Hamiltonian for a nonzero potential energy, while the cases of positive and negative potential energies are analysed separately. Then, we develop the general polytropic-barometric formula that describes the profiles of density, temperature, and thermal pressure. Furthermore, it is shown how the kappa and polytropic indices can be derived from observational measurements of the temperature altitude gradient. As an example, we calculated the kappa κ ≈ 3.35 and polytropic γ ≈ 0.74 indices of the terrestrial atmosphere at ∼100 km, revealing the existence of heating processes that add thermal energy to atmospheric particles.     

Effect of Pump Area on Lasing Modes in Active Random Media

We investigate the effect of pump area on lasing modes in an active random medium. Considering the structure characteristics in a real experimental system, the random medium is divided into two regions, i.e. pump and non-pump areas. The dependence of lasing modes on the pump area is qualitatively explained by means of the model in which the lasing is ascribed to the interaction of the complex localized modes in the active random medium with local aperiodic quasi-structure with appropriate pump light. There exist different pump sizes for lasing with different modes. As the pump size decreases in this random system, the pump threshold of the lasing modes increases. There are different lasing modes in different excitation regions in this random system. This gives us some information about the dependence of lasing modes on pump areas in active random media.     

Observation of gain at 54.2 Å on balmer-alpha transition of hydrogenic sodium

Planer stripe and foil targets coated with NaF were irradiated with high intensity 351 nm laser radiation of 130 ps duration. Time-integrated as well as time-resolved measurement of gain on NaXIH at 54.2Å were made. A time-integrated gain of 1.2 _–1.1 ^+0.8 cm^–1 and a time-resolved peak gain of 3.2±1.0 cm^–1 were obtained. A detailed account of the experimental procedures for determination of gain is given.     

Pump-Induced Lasing Wavelength Shift in Er/Yb Codoped Fiber Grating Lasers

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Mechanism of Low Threshold Lasing of Dye Solution Embedding in Nanoparticle Fractal Aggregates

We study the single-photon and two-photon induced emission properties of dye solution embedded with nanoparticle fractal aggreagates.The spectral and temporal experimental results show that the lasing threshold of single photon absorption of a neat dye solution;while that of two-photon absorption does not.These experimental results imply that this low threshold single-photon absorption lasing mainly results from the mechanism of random walking,instead of Anderson localization.unless somthing about two-photon induced emission is unknown.