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The requirement for a wideband recording capability for instrumenting electromagnetic fields with nanosecond rise time perturbations and long duration reactions lead to the development of a modulated laser beam analog recorder. The original concept of the recorder yielded 100 MHz bandwidth records of Â±40 db dynamic range of approximately 25 Â¿sec duration but required synchronization of the event to the rotating mirror camera of the recorder. Normalization of data required digital computer processing of densitometer conversion of film density data to analog electrical signal. An improvement of the original system, which permits continuous recording up to several minutes at 100 Mbit digital writing solves the major shortcomings of the analog recorder. Using techniques of signal conditioning and laser beam splitting and modulation of the previous system, the data stream is split into four channels recorded simultaneously and continuously on moving 70 mm film in a four-to-one interlace pattern. Each channel is organized into discrete blocks with data synchronizing words to provide block and timing identification. The physical arrangement of the recorder is such that film readout is effected on the same transport deck. Simultaneously scanned data tracks generate a parallel serial data train which is buffered, multiplexed, and recombined to produce the serial data stream.