Analysis of H-alpha flare spectra

Spectrographs of the H-alpha line taken at 15 second intervals from the event of 5 Sept. 1973 were interpreted by comparison with synthetic profiles. A sequence of 27 high resolution H alpha profiles was obtained from the second brightest flare kernel. The profiles were generally self reversed with a maximum peak intensity of 1.16 x continuum and a maximum central intensity of .91 x continuum. The line characteristics such as red and violet peak intensities and positions, center shifts and wing intensities were tabulated. Synthetic H-alpha profiles were generated from a finite layer assuming simple parameteric forms for the source function and velocity field. The velocity chosen always decreased with optical depth and had the same sign. For absorption profiles, bisector shifts were calculated for a variety of velocities. The velocity field and source function were derived as a function of optical depth and time

Analysis of simultaneous Skylab and ground based flare observations

HeI and HeII resonance line data from Skylab were reduced, analyzed and compared with HeI D3 line intensities taken simultaneously from the Lockheed Rye Canyon Solar Observatory. Computer codes were developed for the calculation of total He line intensities and line profiles from model flare regions. These codes incorporate simultaneous solution of the line and continuum transport equations as needed together with the statistical equilibrium equations for a 30 level HeI, HeII, HeIII system. The energy level model consists of all terms through principal quantum number four. Interpretation of the observed data in terms of these parametric solutions and with simultaneous solution of the transport equations are discussed

Study of helium emissions from active solar regions

A theoretical study is made of the visible and UV line radiation of He I atoms and He II ions from a plane-parallel model flare layer. Codes were developed for the solution of the statistically steady state equation for a 30 level He I - II - III model, and the line and continuum transport equations. These codes are described and documented in the report along with sample solutions. Optical depths and some line intensities are presented for a 1000 km thick layer. Solutions of the steady state equations are presented for electron temperatures 10,000 to 50,000 K and electron densities 10 to the 10th power to 10 to the 14th power/cu cm

Theoretical aspects of intense field harmonic generation

We present theoretical studies of high-order harmonic generation in a rare-gas medium. The experimental results obtained at Saclay with a 1064 nm Nd-YAG laser in the 1013 W cm-2 intensity range are summarized. The harmonic emission strengths first decrease rather steeply for the first orders, then form a long plateau up to the 21st harmonic in xenon, or up to the 33rd harmonic in argon, before decreasing again rather abruptly. The theoretical description of these experiments consists first in the calculation of the photoemission spectra emitted by a single atom. The spectra are obtained by numerically integrating a time-dependent Schrôdinger equation for the laser-excited rare-gas atom. Second, one must account for collective effects in the medium, described by Maxwell’s equations. A theoretical framework for describing the generation and propagation of harmonics in strong laser fields is developed. A numerical solution of the propagation equations for the harmonic fields in xenon at 1064 nm provides results which agree well with experimental data. We discuss the role of phase matching in the high-order harmonic generation experiments. The main conclusion is that phase matching is determined not only by the variation of the phases of the interfering fields in the non-linear medium, but also by the variation of the amplitudes throughout the medium. We find orders of magnitude improvement in phase matching in a strong-field regime compared with the perturbative limit. © 1991 IOP Publishing Ltd

High-order harmonic generation from atoms and ions in the high intensity regime

We present calculated optical harmonic spectra for atoms and ions in the high intensity regime to current short-pulse experiments. We find that ions can produce harmonics comparable in strength to those obtained from neutrals, and that the emission extends to much higher order. Simple scaling laws for the strength of the harmonic emission and the maximum observable harmonic are suggested. These results imply that the photoemission observed in recent experiments in helium and neon contains contributions from ions as well as neutrals. © 1992 The American Physical Society

Field Guide to Joint Patterns and Geomorphological Features of Northern Ohio

Author Institution: Department of Geology, University of Toledo, Department of Geological Sciences, Wright State University, Department of Geology, Bowling Green State University and France Stone CompanyBedrock in northern and northwestern Ohio consists of Middle Paleozoic carbonates and shales and is pervasively jointed. The regional joint pattern and chronology, established by the characteristics of joint traces, mineralization, and surfaces, reveal a complex history of fracture development. Joint studies along the north-south trending Bowling Green fault zone indicate that northwest-trending joints formed first in response to extensional stresses associated with differential dip-slip movement in this fault zone, or by left lateral movement along this zone

Interference effects in above-threshold ionization from diatomic molecules: determining the internuclear separation

We calculate angle-resolved above-threshold ionization spectra for diatomic molecules in linearly polarized laser fields, employing the strong-field approximation. The interference structure resulting from the individual contributions of the different scattering scenarios is discussed in detail, with respect to the dependence on the internuclear distance and molecular orientation. We show that, in general, the contributions from the processes in which the electron is freed at one center and rescatters off the other obscure the interference maxima and minima obtained from single-center processes. However, around the boundary of the energy regions for which rescattering has a classical counterpart, such processes play a negligible role and very clear interference patterns are observed. In such energy regions, one is able to infer the internuclear distance from the energy difference between adjacent interference minima.Comment: 10 pages, 8 figures; discussions slightly modified and an additional figure inserted for clarit

Non-Sequential Double Ionization is a Completely Classical Photoelectric Effect

We introduce a unified and simplified theory of atomic double ionization. Our results show that at high laser intensities ($I \ge 10^{14}$ watts/cm$^2$) purely classical correlation is strong enough to account for all of the main features observed in experiments to date

Influence of Phase Matching on the Cooper Minimum in Ar High Harmonic Spectra

We study the influence of phase matching on interference minima in high harmonic spectra. We concentrate on structures in atoms due to interference of different angular momentum channels during recombination. We use the Cooper minimum (CM) in argon at 47 eV as a marker in the harmonic spectrum. We measure 2d harmonic spectra in argon as a function of wavelength and angular divergence. While we identify a clear CM in the spectrum when the target gas jet is placed after the laser focus, we find that the appearance of the CM varies with angular divergence and can even be completely washed out when the gas jet is placed closer to the focus. We also show that the argon CM appears at different wavelengths in harmonic and photo-absorption spectra measured under conditions independent of any wavelength calibration. We model the experiment with a simulation based on coupled solutions of the time-dependent Schr\"odinger equation and the Maxwell wave equation, including both the single atom response and macroscopic effects of propagation. The single atom calculations confirm that the ground state of argon can be represented by its field free $p$ symmetry, despite the strong laser field used in high harmonic generation. Because of this, the CM structure in the harmonic spectrum can be described as the interference of continuum $s$ and $d$ channels, whose relative phase jumps by $\pi$ at the CM energy, resulting in a minimum shifted from the photoionization result. We also show that the full calculations reproduce the dependence of the CM on the macroscopic conditions. We calculate simple phase matching factors as a function of harmonic order and explain our experimental and theoretical observation in terms of the effect of phase matching on the shape of the harmonic spectrum. Phase matching must be taken into account to fully understand spectral features related to HHG spectroscopy