NASA Scientific and Technical Aerospace Reports

We discuss the temporal and spectral properties of self-amplified spontaneous emission (SASE) utilizing an energychirped
electron beam. A short temporal pulse is generated by using a monochromator to select a narrow radiation bandwidth
from the frequency chirped SASE. For the filtered radiation, the minimum pulse length is limited by the intrinsic SASE
bandwidth, while the number of modes and the energy fluctuation can be controlled through the monochromator bandwidth.
Two cases are considered: (1) placing the monochromator at the end of a single long undulator; (2) placing the monochromator
after an initial undulator and amplifying the short-duration output in a second undulator. We analyze these cases and show that
tens of femtosecond x-ray pulses may be generated for the linac coherent light source.
NTIS
Free Electron Lasers; Electron Beams
20040071085 Brookhaven National Lab., Upton, NY
Saturation of a High-Gain Single-Pass FEL
Krinsky, S.; 2003; 12 pp.; In English
Report No.(s): DE2004-15006737; BNL-71912-2003-CP; No Copyright; Avail: Department of Energy Information Bridge
We study a perturbation expansion for the solution of the nonlinear one-dimensional FEL equations. We show that in the
case of a monochromatic wave, the radiated intensity satisfies a scaling relation that implies, for large distance z traveled along
the undulator, a change in initial value of the radiation field corresponds to a translation in z (lethargy). Analytic continuation
using Pade approximates yields accurate results for the radiation field early in saturation.
NTIS
Free Electron Lasers; High Gain; Saturation; Perturbation
20040071090 Helsinki Univ. of Technology, Espoo
Spatial Correlations and Partial Polarization in Electromagnetic Optical Fields: Effects of Evanescent Waves
Setala, T.; 2003; 60 pp.; In English
Report No.(s): PB2004-105764; No Copyright; Avail: CASI; A04, Hardcopy
In this thesis, partial polarization and spatial correlation properties of electromagnetic optical fields are investigated. The
emphasis is on near fields which exist only within the distance of the light wavelength from the emitting or scattering object.
In the near-field region, the contribution of the evanescent (non-radiating) waves is overwhelming compared to the
propagating waves that can be observed far from the source. Certain fundamental issues related to the optical near-fields are
studied. The decomposition of the free-space Green tensor into its evanescent and propagating parts is performed. This issue
is of importance in near-field optics and it has attracted considerable attention in the recent literature. Another fundamental
issue investigated in the thesis concerns the three-dimensional degree of polarization needed to characterize of electromagnetic
fields having arbitrary planar or non-planar wave structures. The physical interpretation of the concept is presented, and its
differences in comparison with the conventional two-dimensional formulation of the degree of polarization are brought out.
The theory is applied to investigate the effects of evanescent waves and resonant surface waves on the polarization state of
the near fields generated by some thermal half-space sources. The thesis also includes a study of the partial polarization and
spatial correlation properties of homogeneous free electromagnetic fields. The fields are modelled as an isotropic distribution
of angularly uncorrelated and, in the 2D-sense, unpolarized plane waves propagating within a solid angle. When the solid
angle extends over the full space, the spatial correlations are found to be determined by the imaginary part of the associated
Green tensor, and the field is fully unpolarized in the 3D-sense. These results are the same as for black-body fields, although
here no thermal equilibrium is assumed. The same behavior is discovered for any electromagnetic field generated by a
statistically homogeneous and isotropic current distribution, which fluctuates within a medium having a vanishingly small
absorption. For the fields whose electric cross-spectral density tensor is proportional to the imaginary part of the Green tensor,
the degree of coherence has a universal form given by the sinc law.
NTIS
Electromagnetism; Evanescent Waves; Polarized Electromagnetic Radiation; Spatial Distribution; Correlation
20040071093 Lawrence Livermore National Lab., Livermore, CA
Spectral and Imaging Characterization of Tabletop X-ray Lasers
Dunn, J.; Faenov, A. Y.; Pikuz, T. A.; Osterheld, A. L.; Moon, S. J.; Dec. 01, 2000; In English
Report No.(s): DE2004-15005759; UCRL-JC-138687; No Copyright; Avail: National Technical Information Service (NTIS)
We have performed L-shell spectroscopy and one-dimensional (1-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
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