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It is suggested that coherent X-rays can be produced by inverting the electron population in a suitable target, such as Li, through irradiation with X-rays generated by fast electrons traversing an electromagnetic field (as in a storage ring). Conditions to be satisfied by target and radiation parameters are stated, and examples given.
It is suggested that coherent soft X rays can be produced by inverting the electron population in a suitable target, such as Li, through irradiation with X rays generated by fast electrons traversing an electromagnetic field (as in a storage ring). Conditions to be satisfied by target and radiation parameters are stated, and examples given.
Solid state mechanism for generating coherent radiation in ultraviolet and X ray regions
Von Laue and Cowley diffraction theories of coherent diffuse X-ray scattering from random alloys, predicting diffuse intensity singularities at reciprocal lattice points
Microwave impedance measurements for determining space charge waves in semiconductors
Optical harmonic generation and mixing in the gas phase has been proposed as a technique for the generation of coherent radiation in the vacuum ultraviolet and soft X-ray spectral region. At the high field strengths required by these processes the interaction between atoms and the electromagnetic field shows intensity-dependent resonances. In this paper we modify harmonic generation theory to include the effect of these frequency shifts. Closed-form expressions for generated dipole moment, absorption probability, and coherence length are presented. The most important consequences of frequency shifts on resonantly enhanced processes are that the pump laser must be tuned away from the small-field resonance frequency, that the conversion efficiency may saturate, and that the dispersion of the medium may change sign. As an example, the generation of 198-A radiation by a five-photon mixing process in Li(+) is considered.
The paper presents theoretical and observational works in the field of planetary and astrophysical magnetospheres. The magnetospheres of earth and Jupiter are analyzed along with pulsar magnetospheres and X-ray source magnetospheres. Consideration is given to coherent radio emissions in space and astrophysics and collective radio emissions from plasmas. Theories of magnetospheres around accreting compact objects are also presented.
The paper describes the use of nonlinear optical techniques for the generation of coherent radiation at ultraviolet, vacuum ultraviolet, and soft X-ray wavelengths. Mixtures of metal vapors and inert gases, and other mixed gas systems, allow generation to regions of the spectrum where nonlinear optical crystals are opaque; and also allow generations at high incident power and energy densities. Progress is reported on programs aimed at efficient conversion from 1.064 microns to 3547 A, and from 3547 A to 1182 A. To date, the shortest wavelength generated by this technique is 887 A. Theoretical considerations indicate that generation into the soft X-ray region should be possible. Using 1182 A radiation, a holographic grating with a fringe spacing of 836 A has been constructed and examined on an electron microscope.
Pulsed soft X-rays (0.1 to 0.5 keV) with a period of 9 sec and a pulsed fraction that varies between 0 and 100% were detected from the dwarf nova SS Cygni at the peak of an optical outburst. This detection confirms for the first time the supposed high energy origin of optical pulsations seen in erupting dwarf novae. The pulse shape is remarkably sinusoidal for such a large-amplitude oscillation. The X-ray pulsation observed in this outburst is not coherent, in contrast to previous claims for the related optical oscillations.
Natural and controlled whistler-mode signals have been used to study nonlinear mechanisms of wave growth and wave-wave interactions (WWI) in the magnetosphere; three general classes of WWI (triggering, suppression, and entrainment) are identified and interpreted in terms of a model based on cyclotron resonance interaction. This model is also used to estimate the wave field intensity associated with different types of WWI. A new type of triggered emission, the band-limited impulse (BLI) is interpreted in terms of the switching of phase-bunched currents. In addition, an experiment to find a threshold for the excitation of the coherent wave instability is discussed, and observed VLF wave-induced transient bursts of X-rays, light and E-region ionization enhancements are considered with regard to a step function wave interacting with all resonant electrons in a given energy range.
Both SS Cyg and U Gem show enhanced soft X-ray emission (0.1 to 0.5 keV) during optical outbursts. The fact that a large fraction of this emission is pulsed confirms the general expectation that high energy pulsations are the ultimate source of the optical pulsations observed during outbursts of dwarf novae. The present analysis leads to the conclusion that coherent optical oscillations, of the type exhibited by SS Cyg, can be explained by intrinsic phase instability. The quasi-coherent optical pulsations observed for several dwarf novae on the decline from maximum brightness have a behavior similar to the X-ray pulsation in U Gem. It is suggested that all of the optical and X-ray oscillations are produced by the same mechanism.
The status of X-ray observations is summarized in tabular form along with general aspects of X-ray emission. Specific questions that arise when the observed phenomena are pieced together into a coherent picture are presented. Spectral states, transitions, periodic behavior, fluctuations, and bursts are among the topics discussed.
It is proposed that many of the X-ray sources associated with the galactic bulge are accreting neutron stars or black holes with masses of at least about 1 solar mass in ultrashort-period binary systems with very low-mass (no more than about 0.5 solar mass) stellar companions. It is demonstrated that this hypothesis may provide a coherent picture of the evolutionary history and observational properties of these sources, including the apparent lack of conspicuous optical counterparts and the apparent absence of X-ray eclipses.
We examine the large-scale spatial and temporal variations in the emergence of X-ray bright points on the sun, in order to study the global properties of magnetic flux emergence. Major variations in the rate of flux emergence are observed at all solar latitudes, on a time scale of 3-5 months. The most economical explanation of the observations is that the full sun participated in a single large eruptive event during the available 8 month observing period from Skylab in 1973. The peak of this global event corresponds in time to the eruption of a major complex of activity. Moreover, it appears that the only portion of the solar surface which deviates from the above pattern of behavior is the low latitude region in the vicinity of the AR complex; this area shows a temporary depletion immediately following the AR outburst. The high-latitude regions in both hemispheres show the same variation and appear to lead the low-latitude emergence by approximately 1 month.
Considerations made in developing a model of pulsars are explored. Observational data seems to support the argument that pulsar magnetospheres may contain large masses of plasma. The cascade process resulting from pair creation enables one to interpret the X-ray emission from the Crab and Vela pulsars as synchrotron radiation. On the other hand, the optical radiation from the Crab pulsar is best understood as coherent curvature radiation. Radio emission is interpreted as curvature radiation produced by charge bunches moving along magnetic-field lines. Certain tests of this model are proposed.
VLBI radio and X-ray observations were made of the bright X-ray quasar NRAO 140. The radio structure consists of two very compact components plus a more diffuse jet. Based on the standard synchrotron theory, the Compton X-ray emission from one of these compact components was found to exceed the observed value by three orders of magnitude. Since this result is independent of distance and there is no evidence for coherent emission, it is concluded that the component is moving toward us at a relativistic speed with a Lorentz factor exceeding 4. Future observations should reveal superluminal separation of the components, as well as help in determining which components are undergoing relativistic motion.
A Warren-Averbach x-ray line profile analysis was applied to, broadened x-ray diffraction peaks from copper deformed in fatigue. The copper specimens were fatigued by four point bending at various strain amplitudes, and measurements were made at various fractions of the total fatigue life. The analysis results in an estimation of 1) an average coherently diffracting domain size in a direction normal to the diffracting planes; and 2) a strain distribution function. The strain distribution function is in terms of the root mean square strain, <ϵ^(2)> where ϵ is averaged over a given distance at all points in the diffracting crystals. This rms strain is expressed as a function of averaging distance for a direction normal to the diffracting planes. The rms strains were found to be a function of the fatigue strain amplitude level, increasing with amplitude and reaching a maximum limiting value during the first 2% of the fatigue life. The strains were normally larger in the 4lO0 direction compared to the <111> direction and the absolute values were quite small. These results may be explained by assuming the dislocations are present in the form of dipoles because the lattice strain around a dipole is much less than around single dislocations. Conclusions arrived at in this analysis are in agreement with current theories of fatigue damage in metals. The result that maximum hardening is achieved during the initial few percent of the fatigue life is confirmed by many other investigators using entirely different analytical techniques. It is felt that the structure of the material is changing during this initial hardening stage to an eventual steady state characteristic of the testing conditions. A unique substructure is developed which thereafter persists, and the remainder of the fatigue test is taken up by crack propagation through this substructure until ultimate failure occurs by fracture. The formation of this steady state structure is dependent on the maximum fatigue strain amplitude and on the frequency and temperature of cycling for a particular material.
A computerized technique is proposed for obtaining cross-sectional images of the dynamic spatial distribution of X-ray attenuation covering the entire anatomic extent of the thorax and its contents in living dogs with a resolution of 1 mm and at time intervals of 1/60 sec. Use is made of an X-ray imaging chain which is a new high-performance video-fluoroscopic system, unique in its design and construction and called SSDSR for single source dynamic spatial reconstructor. This dynamic spatial reconstruction system is shown to provide the temporally and spatially coherent multiple cross sections required to obtain the full three-dimensional anatomic and simultaneous hemodynamic information necessary for detailed quantitative analyses of regional cardiopulmonary and vascular functions in both basic investigations of animals and clinical diagnostic applications to patients. Numerous photographs supplement the text.