Retarding field energy analyser ion current calibration and transmission

International audienceAccurate measurement of ion current density and ion energy distributions (IED) is often critical for plasma processes in both industrial and research settings. Retarding field energy analyzers (RFEA) have been used to measure IEDs because they are considered accurate, relatively simple and cost effective. However, their usage for critical measurement of ion current density is less common due to difficulties in estimating the proportion of incident ion current reaching the current collector through the RFEA retarding grids. In this paper an RFEA has been calibrated to measure ion current density from an ion beam at pressures ranging from 0.5 to 50.0 mTorr. A unique method is presented where the currents generated at each of the retarding grids and the RFEA upper face are measured separately, allowing the reduction in ion current to be monitored and accounted for at each stage of ion transit to the collector. From these I-V measurements a physical model is described. Subsequently, a mathematical description is extracted which includes parameters to account for grid transmissions, upper face secondary electron emission and collisionality. Pressure-dependant calibration factors can be calculated from least mean square best fits of the collector current to the model allowing quantitative measurement of ion current density

Theoretical enquiry into the use of data entropy methods for optoelectronic-fiber system-digital design

The paper begins an investigation into the utility of the data entropy based 'quality budget method for optical telecommunications has recently arisen through the growing use of analogue optical amplifiers in what previously were exclusively digital fiber communication systems. The engineering of these now binary systems perhaps requires more than the established analysis tools of 'error budgets' and 'rise-time budgets'. The alternative 'quality budget' proposed and theoretically investigated here for the first time, seeks to directly link the measured output of systems to the measured performance of the system. This approach has previously been used very successfully to develop an amplitude modulated fiber optic system and delivered a very high 12-bit performance level for this AMFOS system. This new digital system application of the quality budget method provides a theoretical illustration of some of the most significant optoelectronic noise and loss components for both optoelectronic detectors and the laser source used in telecommunication systems. Demonstrations of using this approach of handling of the binary analogue and digital features are shown. Space restrictions do not allow a comprehensive analysis of the telecommunication issues and therefore simple quick reference tables of new results are used to condense the presentation of material. The data entropy description of digital signals is then investigated. The paper concludes with brief considerations into the advantages of this approach for the analysis of digital fiber systems using this two-sided approach to system performance quantification applying this integrated methodology for networking applications