18 research outputs found
Effective Hamiltonian and unitarity of the S matrix
The properties of open quantum systems are described well by an effective
Hamiltonian that consists of two parts: the Hamiltonian of the
closed system with discrete eigenstates and the coupling matrix between
discrete states and continuum. The eigenvalues of determine the
poles of the matrix. The coupling matrix elements
between the eigenstates of and the continuum may be very
different from the coupling matrix elements between the eigenstates
of and the continuum. Due to the unitarity of the 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 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 W/cm.
Our experimental observations of X-ray spectral line profiles
confirmed the presence of a great quantity of high-energy ions
(1 MeV) in laser plasma. Besides, by the
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 (I10 W/cm,
= 1.053 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