Electron-positron pair creation by high-energy photons incident near crystalline planes

The process of electron-positron pair creation by polarized photons incident on a single crystal at a small angle θ0 to the crystalline planes is considered. A general description of the process, valid at any θ0, is obtained. The limiting cases are comprehensively analysed: 1. of small θ0 where the constant field approximation is applicable; 2. of relatively large θ0 where the theory of coherent pair creation is applicable; a modification of this theory with a broader range of applicability has been derived. A general description of the polarization effects is given and the prospects of using crystals to obtain and to measure the polarization of photons are studied. (orig.)