Reflectron second-order, dual-stage

Second-order solutions are also possible for the dual-stage source (Figure 10.3c), and they result in a much shorter optimal drift length. This configuration is rarely used in a simple linear spectrometer, but can be used to form an intermediate virtual point source for a reflectron (see below). A shorter, higher-order focal plane has also been used in the development of instruments of compact size. 

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