Cause Of Gain Research Articles

Optical gratings in the collective interaction between radiation and atoms, including recoil and collisions

The introduction of collisions and of a thermal distribution for the atomic momentum in the model for the Collective Atomic Recoil Laser (CARL) is at the origin of important modifications in the interpretation of the mechanisms that give rise to the amplification of the backreflected wave. It is shown that the atomic density grating, considered to be the cause of gain in CARL, disappears in the presence of collisions, while other gratings—in population and polarization phase—survive. While the population grating appears to be merely a consequence of the collective interaction, the latter is the likely cause for the instability. Finally, simulations show that models that make use of an exponential relaxation mechanism for the atomic momentum,rather than accounting for collisions explicitly, largely overestimate the strength of the interaction.

The Declining Drain Line Lengths Circuit--A Computer Derived Design Concept Applied to a 2 26.5-GHz Distributed Amplifier

The principle of the declining drain line lengths has emerged as a successful concept in the pursuit of improved gain flatness and bandwidth. The optimized performance parameters of an identical links gain module are compared to those of a declining drain line lengths gain module, and the advantages of one design principle over the other are discussed. In addition, the paper studies the RF voltages and currents of the circuits' GaAs MESFETs and draws some qualitative conclusions as to the causes of gain limiting when approaching nonlinear operation. Finally, experimental results of a power module based on the declining drain line lengths principle are reported. The hybrid amplifier which incorporates five active devices with 0.25-µm gates achieves a small signal gain of G = 6.1+-0.6 dB from 2-27 GHz. Measurements of its output power, reflection coefficients and noise figure are afso discussed.