The problem of Rainich for null fields is examined, and it is found that for particular geometries the electromagnetic field is not unique. In the special case where the propagation and polarization vectors are harmonic, the geometry admits an electromagnetic potential which excludes the existence of magnetic monopoles. An explicit solution for a null electromagnetic plane wave of arbitrary pulse shape is obtained. It is found that there is generated no gravitational field external to the pulse.
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- 1 - Physical Sciences ; 2 - Physics and Astronomy ; 3 - General Physics and Astronomy