Measuring apparatus for monitoring the position of the center of mass of a semiconductor wafer is disclosed. Coherent dual scanning laser systems are disclosed and some applications thereof. The linear conversion process of an F function corresponding to each of the plurality of rounds is performed as a linear conversion process which employs an MDS matrix, and a linear conversion process is carried out which employs a different MDS matrix at least at each of consecutive odd number rounds and consecutive even number rounds. A cathode electrode is formed on the surface of the n+ cathode layer.