Absolute energy measurement in e/sup -/e/sup +/ colliders

A technique based on the Compton scattering of linearly polarized visible light is proposed for measuring the absolute energy of an electron beam in a linear collider. In the vicinity of 90 degrees in the rest frame of the electron the ratio of the cross-section for different linear light polarizations depends strongly on the absolute energy of the beam. This is especially true when the backscattering rates with light polarized perpendicular to the scattering plane is compared with light polarized in the scattering plane. As a result, the absolute energy of the beam can be determined to a high degree of precision by measuring the ratio of two counting rates. Using a strong laser field (e.g. that in a Fabry-Perot resonant cavity), the measurement can be performed in a fraction of a second. Examples of possible practical arrangements are given.