Distributed feedback X-ray lasers in single crystals

There are two main obstacles in the way of obtaining laser action in the X-ray region. The first involves the pumping necessary to obtain the critical inversion. The second one is that of the optical feedback

Virtual dielectric waveguide mode description of a high-gain free-electron laser I: Theory

A set of mode-coupled excitation equations for the slowly-growing amplitudes of dielectric waveguide eigenmodes is derived as a description of the electromagnetic signal field of a high-gain free-electron laser, or FEL, including the effects of longitudinal space-charge. This approach of describing the field basis set has notable advantages for FEL analysis in providing an efficient characterization of eigenmodes, and in allowing a clear connection to free-space propagation of the input (seeding) and output radiation. The formulation describes the entire evolution of the radiation wave through the linear gain regime, prior to the onset of saturation, with arbitrary initial conditions. By virtue of the flexibility in the expansion basis, this technique can be used to find the direct coupling and amplification of a particular mode. A simple transformation converts the derived coupled differential excitation equations into a set of coupled algebraic equations and yields a matrix determinant equation for the FEL eigenmodes. A quadratic index medium is used as a model dielectric waveguide to obtain an expression for the predicted spot size of the dominant system eigenmode, in the approximation that it is a single gaussian mode.Comment: 14 page

Computation of bipolar transistor base parameters for general distribution of impurities in base

A procedure is suggested by which dc and ac base gain parameters can be computed for general impurity distributions in the base. The procedure consists of solving the current equation as series in the recombination time (1/τ). The series expansion coefficients are computed for a Gaussian distribution up to first order, along with the resulting base alpha transport factor and the transit time. Mobility variation with impurity concentration is also taken into account. Explicit expressions for cutoff frequencies and excess phase shift ω_T, ω_ɑ, ω_β, m) are developed using the coefficients of the series expansion up to the second order. Computation of these parameters for the case of an exponential distribution, with and without assumption of diffusion coefficient variation, results in new expressions and values

Free-Electron–Bound-Electron Resonant Interaction

Here we present a new paradigm of free-electron–bound-electron resonant interaction. This concept is based on a recent demonstration of the optical frequency modulation of the free-electron quantum electron wave function (QEW) by an ultrafast laser beam. We assert that pulses of such QEWs correlated in their modulation phase, interact resonantly with two-level systems, inducing resonant quantum transitions when the transition energy ΔE=ℏω₂₁ matches a harmonic of the modulation frequency ω₂₁=nω_b. Employing this scheme for resonant cathodoluminescence and resonant EELS combines the atomic level spatial resolution of electron microscopy with the high spectral resolution of lasers

Monolithic solid-state traveling-wave amplifier

A new monolithic structure for solid-state traveling-wave amplifiers is proposed, which promises efficient interaction between a drifting charge carrier stream and a slow electromagnetic wave component. The suggested configuration is potentially suitable for operation in the far-ir frequency regime. A one-dimensional analysis of the interaction between the electromagnetic waveguide mode and the carrier current is presented, including the loss contribution due to the nonsynchronous space harmonics of the electromagnetic mode