Effective Hamiltonian and unitarity of the S matrix

The properties of open quantum systems are described well by an effective Hamiltonian ${\cal H}$ that consists of two parts: the Hamiltonian $H$ of the closed system with discrete eigenstates and the coupling matrix $W$ between discrete states and continuum. The eigenvalues of ${\cal H}$ determine the poles of the $S$ matrix. The coupling matrix elements $\tilde W_k^{cc'}$ between the eigenstates $k$ of ${\cal H}$ and the continuum may be very different from the coupling matrix elements $W_k^{cc'}$ between the eigenstates of $H$ and the continuum. Due to the unitarity of the $S$ matrix, the \TW_k^{cc'} depend on energy in a non-trivial manner, that conflicts with the assumptions of some approaches to reactions in the overlapping regime. Explicit expressions for the wave functions of the resonance states and for their phases in the neighbourhood of, respectively, avoided level crossings in the complex plane and double poles of the $S$ matrix are given.Comment: 17 pages, 7 figure

Directed inward beams of ions in laser produced plasma

We investigated the ion characteristics in picosecond laser plasma at laser radiation intensity of up to $2\times 10^{18}$ W/cm$^{2}$. Our experimental observations of X-ray spectral line profiles confirmed the presence of a great quantity of high-energy ions ($\sim$1 MeV) in laser plasma. Besides, by the $L_{y\alpha }$ Doppler profile's red shift we revealed the high-energy ion motion directed inward the target. For this phenomenon we suggest our theoretical model. The high energy “tail” in the energy spectrum of ions in laser plasmas can be explained by the pinch effect. The effective way for production of beams of charged particles in laser plasmas is the electric drift of these particles in electromagnetic fields generated in the laser-produced plasmas

Spectral and imaging characterization of tabletop X-ray lasers

We have performed L-shell spectroscopy and one-dimensional (l-D) imaging of a line focus plasma from a laser-heated Fe polished slab using the tabletop COMET laser system at the Lawrence Livermore National Laboratory. These plasmas are used to generate a Ne-like Fe transient gain x-ray laser that is recorded simultaneously. A spherically-curved crystal spectrometer gives high resolution x-ray spectra of the n = 3 – 2 and n = 4 – 2 resonance lines with l-D spatial resolution along the line focus. Spectra are presented for different laser pulse conditions. In addition, a variety of x-ray imaging techniques are described. We discuss imaging results from a double-slit x-ray camera with a spherically-curved crystal spectrometer. We show a high resolution Fe [MATH] spectrum from the x-ray laser target that indicates the presence of hot electrons in the x-ray laser plasma

X-ray spectroscopic study of nonequilibrium laser produced plasma in porous targets of low average density

New experimental results on laser irradiation (I$\,{\le}\,$10$^{14}$ W/cm$^{2}$, $\lambda$ = 1.053 $\mu$m) of low-density fibrous agar are presented. X-ray spectrometers with spherically bent mica crystals were used for measuring with high spectral resolution the line spectra of multicharge ions. Detailed analysis of the measured spectra made it possible to determine the temperature of electrons and ions in hot plasma created in laser irradiated low-density samples in dependence on average material density and average intensity within a focal spot. Significant difference between ion and electron temperatures is found for the whole range of experimental conditions