High Interaction Efficiency Research Articles

Density dependence of carrier-carrier-induced intersubband scattering inGaAs/AlxGa1−xAsquantum wells

Photoluminescence lifetimes of the $n=2$ level in a large quantum well show a clear nonmonotonic dependence on the density of optically generated carriers. Varying the power density over five orders of magnitude we prove directly the high efficiency of carrier-carrier interaction for intersubband scattering when longitudinal-optical phonon emission is suppressed. For low densities, the observed $n=2$ decay times get shorter (from 40 down to 5 ps) as the density is increased. At high densities Pauli blocking reduces significantly the intersubband scattering rates.

Three-dimensional nonlinear analysis of an E× B drifting electron laser

In this paper we numerically investigate the nonlinear evolution of the E × B drifting electron laser (DEL) [1, 2] for an amplifier configuration in which an electron beam propagates through a periodic magnetic field (wiggler) and undergoes a relativistic E × B drift in orthogonal static electric and magnetic fields. A set of coupled nonlinear differential equations is given in three dimensions which controls the self-consistent evolution of TE modes in a rectangular waveguide as well as the trajectories of an ensemble of electrons. Our numerical simulations are conducted to model a 35 GHz amplifier with an electron beam energy of 3.5 MeV. The results show that the radiation energy in the DEL mainly comes from the change in the kinetic energy of the electron beam, and the DEL, compared with the free-electron laser (FEL) with similar operating parameters, has higher interaction efficiency and peak power.

Analysis of velocity-matched Ti:LiNbO3 optical intensity modulators with an extended point-matching method

The point-matching method has been extended to analyse a travelling-wave electrode structure for shielded velocity-matched Ti:LiNbO3 Mach-Zehnder optical modulators. This method provides a simple and fast approach to analysing the coplanar waveguide with buffer layer, cover shield, and electrodes of finite thickness. The calculated characteristic impedances and microwave effective indices agree well with those obtained using the spectral domain technique and the finite-element method. It is found that in the coplanar waveguide without cover shield it is difficult to achieve velocity matching. The coplanar waveguide with cover shield can be used to achieve velocity matching, but the corresponding characteristic impedance is lower than 50Ω. Both velocity matching and impedance matching can be obtained using a narrow centre electrode. The calculated electric field has been used to estimate the modulation efficiency of the device. Velocity matching can be achieved by adjusting the height of the cover shield, but a compromise must be made between high interaction efficiency and low microwave reflection when choosing the buffer layer thickness and the electrode thickness.

On one mechanism of spurious oscillations in high-power gyrotrons

One of the problems encountered in the design of high-power gyrotrons is the need to ensure stable single-mode generation. The conditions of spurious self-excitation in a gyrotron resonator have been studied fairly completely, and methods for its suppression have been developed (see Petelin [1] and Nusionvich [2], for example). At the same time, stable gyrotron operation can also be disrupted by the generation of spurious oscillations in the transition region between the electron gun and the resonator, where the electromagnetic field is nonuniform. A theoretical basis for this assumption is provided by results [1, 3, 4] indicating a fairly high efficiency of interaction of a high-frequency field with an electron current guided by a nonuniform magnetostatic field.

A theory of multiwave devices on coherent magnetic bremsstrahlung of relativistic electron beams

Presented are the results of numerical simulation of coherent microwave radiation sources, based on magnetic bremsstrahlung of the relativistic electron beam. For the description of electromagnetic field the Fourier analysis of delayed potentials is used. Angular characteristics of collective radiation were studied. The possibility of high efficiency of multiwave interaction is demonstrated.