Accurate triplet phase determination in non-perfect crystals--a general phasing procedure

A completely different approach to the problem of physically measuring the invariant triplet phases by three-beam X-ray diffraction is proposed. Instead of simulating the three-beam diffraction process to reproduce the experimental intensity profiles, the proposed approach makes use of a general parametric equation for fitting the profiles and extracting the triplet phase values. The inherent flexibility of the parametric equation allows its applicability to be extended to non-perfect crystals. Exploitation of the natural linear polarization of synchrotron radiation is essential for eliminating systematic errors and to provide accurate triplet phase values. Phasing procedures are suggested and demonstrative examples from simulated data are given.