Multiphoton effects in energy loss spectra

The effect of radiation of many photons by a single electron traversing a target is discussed. When the summary energy of emitted photons (the energy loss spectrum) is measured only, the photon spectrum is distorted compared to the photon spectrum in one interaction. The influence of this effect is discussed for the cases (1) bremsstrahlung (described by the Bethe-Heitler formula), (2) the strong Landau-Pomeranchuk-Migdal effect, and (3) the transition radiation. The qualitative picture of the phenomenon is discussed in detail. A comparison with the recent SLAG experiment in a relatively thick target (2.7% of the radiation length), where the effect of the emission of many photons by a projectile is very essential, shows perfect agreement between the theory and data. [S0556-2821(99)01703-8].