Electron channeling effects can create measurable signal intensity variations in all product signals that result from the scattering of the electron beam within a crystalline specimen. Of particular interest to the X-ray microanalyst are any variations that occur within the characteristic X-ray signal that are not directly related to a specimen composition variation. Many studies have documented the effect of crystallographic orientation on the local X-ray yield; however, the vast majority of these studies were carried out on thin foil specimens examined in transmission. Only a few studies have addressed these effects in bulk specimen materials, and these analyses were generally carried out at common scanning electron microscope microanalysis overvoltages (>1.5). At these overvoltage levels, the anomalous transmission effect is weak. As a result, the effect of electron channeling on the characteristic X-ray signal intensity has traditionally been overlooked in the field of quantitative electron probe microanalysis. The present work will demonstrate that electron channeling can produce X-ray variations of up to 26%, between intensity maxima and minima, in low overvoltage X-ray microanalyses of bulk specimens. Intensity variations of this magnitude will significantly impact the accuracy of qualitative and quantitative X-ray microanalyses at low overvoltage on engineering structural materials.

Anomalous absorption of an intense short laser pulse in overdense plasmas is analyzed with a stochastic theory. A diffusion equation describing a time evolution of the electron distribution function is derived. From the equation it is shown that the electron distribution function becomes anisotropic in the momentum space, which gives rise to the absorption of the energy. The diffusion is not dominant in the pz direction, which is longitudinal to the vacuum-plasma boundary, rather it is dominant in the px direction, which is transverse to the boundary. However, the diffusion in pz enhances the absorption. Analytical expressions of the absorption coefficient and skin depth are obtained for the anomalous skin effect regime (ω02c2 << ωp2ve2), which evolves in time as the electron distribution becomes anisotropic. The asymptotic value of the absorption coefficient is proportional to [square root]I. The temperature and density dependence of the absorption coefficient is also discussed.