Characterization of a Hadamard transform time-of-flight mass spectrometer

A pseudorandom time-of-flight method (also called the cross-correlation method) has been used to perform time-of-flight mass spectrometry with a duty cycle of 50%. Modulation of an ion beam is accomplished by deflecting the ion beam with an interleaved comb of oppositely charged elements. Maximum-length pseudorandom sequences based on Hadamard-type difference sets are produced by feedback shift register circuitry and used for ion beam modulation. The inverse transformation of the recorded signal is carried out speedily with the help of the fast Hadamard transform, which allows real-time monitoring of the mass spectrum. The components of the instrument are described, and its performance is characterized. Trajectory simulations are found to be in good agreement with experimental findings, which aids in understanding the modulation dynamics. It is found that the wire comb modulator can be modeled as a set of ideal deflection plates of length 0.875 l, where l is the spacing between oppositely charged wires. (C) 2000 American Institute of Physics. [S0034-6748(00)00403-2].