Improved Electrical Differentiation of Retarding Potential Measurements

An improved system for obtaining differential spectra from retarding potential measurements by the superposition of a small ac signal on the retarding voltage has been developed. The principal improvements are the choice of the point of injection of the modulation signal, the use of a low impedance preamplifier to improve the accuracy of the energy scale, and the use of a synchronous detector to improve the stability and reduce the effect of noise. The energy profile of a 15‐kev electron beam and the characteristic energy loss spectra in collodion and aluminum have been measured. The quality of these measurements illustrates the over‐all performance of the present system.