  A novel imaging principle based on the interaction of electromagnetic waves
with a beam of relativistic electrons is proposed. Wave-particle interaction is
assumed to take place in a small spatial domain, so that each electron is only
briefly accelerated by the incident field. In the one-dimensional case the
spatial distribution of the source density can be directly observed in the
temporal spectrum of the scattered field. Whereas, in the two-dimensional case
the relation between the source and the spectrum is shown to be approximately
the Radon transform.
