Backscattered supercontinuum emission from high-intensity laser-plasma interactions.
We performed high-intensity subpicosecond laser-plasma interaction experiments to examine nonlinear scattering mechanisms in underdense plasmas. At incident laser intensities of 2 x 10(18) W/cm(2) the stimulated-Raman-backscattered spectrum exhibited an extremely broad, supercontinuumlike structure (Deltaomega/omega(0) > 1) extending from ~500 to >1200 nm (limited only by detector sensitivity). Large-amplitude modulations in the spectrum of the backscattered light were measured and are attributed to an interaction of the stimulated-Raman-scattered radiation with ion plasma waves.
Detection of ion plasma waves by collective Thomson scattering.
The first unambiguous experimental detection of ion plasma waves is reported. These short-wavelength ({ital k}{lambda}{sub De}{gt}1), purely electrostatic ion waves were first predicted by Tonks and Langmuir in 1929. The waves are observed in a long-scalelength ({ital L}{gt}10{sup 4}/{ital k}), multiply ionized ({ital Z}=22), laser-produced plasma. The frequency ({omega}), wave number ({ital k}), and amplitude evolution of the ion waves are measured by time-resolved spectroscopy of the scattering from the ion waves of a probe laser beam. The wave frequency is approximately the ion plasma frequency ({omega}{sub {ital pi}}) when {ital k}{lambda}{sub De} exceeds 1, as predicted by the theoretical dispersion relation.
Conserved Quantities of a Class of Nonlinear Difference-Difference Equations
Higher-order conserved quantities of a class of nonlinear difference-difference equations which are related to the discrete-time Toda equation are obtained using the Miura transformations.