This paper describes a new diagnostic technique to decode information contained in the spectral and spatial distribution of photons emitted by fast neutral beam particles and provide an estimate of the 2‐D beam density distribution function in a cross‐sectional slice. By scanning Doppler‐shiftedH&agr;radiation from the fast beam particles at a number of peripheral locations around the beam axis, tomographic reconstructions of the beam distribution with spatial resolution &Dgr;x&bartil;2 cm and time resolution &Dgr;t&bartil;10 ms can be made. Using a maximum entropy reconstruction algorithm (making no symmetry assumptions), experimental reconstructions are presented of the 2‐D profile of the beam generated by the prototype JET source for each of the Doppler‐shifted line radiation components. Applications of this image processing technique in other areas of high‐temperature plasma diagnostic development are discussed briefly.