Resolution and frequency response in secondary emission devices

The resolution of a secondary emission tube is characterized by an equivalent, or effective, current distribution in the beam. This current distribution is defined as that which would cause the actual resolution degradation when landing on the target surface in an ideal way, i.e., without redistribution nor charge-to-potential mapping on the target. A "frequency response" technique is then introduced to measure the equivalent current distribution, and the theoretical responses for two distributions assumed a priori as possible, i.e., the Gaussian and the cosinusoidal, are derived. These findings are compared with experimental results which show that (1) it is legitimate to characterize the resolution of a storage tube by means of its effective distribution, and (2) both the Gaussian and the cosine distribution are good models for the real situation, the former giving a better fit for somewhat defocused beams. The formulas and experimental techniques describe the tube behavior for all values of scanning speed during both the writing and reading cycles, and for all input frequencies. The results can also be used to determine spatial resolution when discontinuous scanning is used.