Second Order In Field Strength Research Articles

Radiation Functionals for Non-stationary Optical Radiation and Their Determination

Investigation of non-stationary optical radiation, by means of a spectrometer or interferometer, results in a signal that is related to a functional of the electric field strength, the so-called radiation functional. The output spectrum of a spectrochronograph (which consists of a grating spectrometer combined with square-law detectors, e.g. a streak camera), depends on a radiation functional of second order in field strength. In the present paper a new general class of second-order radiation functionals is introduced that includes as special cases the time-dependent spectrum and the Wigner distribution function (recently used in treating this problem). Utilizing the aspect of time-ordering in spectral measurement, the suitability of various radiation functionals for the representation of the relationship between the input properties of the radiation and the measured output spectrum is studied. A radiation functional of first order in field strength is also introduced. Making use of a ‘generalized spectro...

Plasma Fluctuations Induced by Subthreshold Pump Fields

We present in this work three equivalent methods to calculate stable plasma density fluctuations induced by a uniform oscillating electric field near the plasma frequency, somewhat below threshold for generation of parametric electrostatic instabilities. The first method is essentially that of Silin and Sanmartin which is based on the electron and ion Vlasov equations, each transformed to their respective oscillating frames of reference, but here we include effects associated with atomicity of the charges to obtain plasma density fluctuations below threshold. The second approach, which is a more straightforward development of the pumped plasma fluctuations, uses the 'dressed test particle' concept and the nonlinear Poisson equation in the frame of reference oscillating with the electrons. These equations are given for any number of waves and the two results agree exactly. The third and most demanding derivation undertaken here is a modified DuBois–Goldman theory, limited to three waves plus pump, developed by one of us from the rest frame nonlinear Poisson equation for parametric stability analysis. Contrary to an assertion by Hagfors and Gieraltowski, the modified DuBois–Goldman method gives the same results as the other two to second order in field strength.

Collision Integral for a Plasma in a Strong Magnetic Field

Starting from the Bogoliubov-Born-Green-Kirkwood-Yvon hierarchy of statistical mechanics, we derive the magnetic-field dependence of the collision integral to second order in field strength. The field is sufficiently strong to make the Larmor frequency of the same order as the plasma frequency. The calculation is carried out explicitly for a Landau plasma (small-momentum-transfer regime). The simplicity of the result makes it particularly suitable for calculating transport coefficients for a plasma.