Observation of Phase Change of X-ray Polarizability in Rocking Curves

By tuning the X-ray energy from synchrotron radiation very close to the K-absorption edges of Ga and As, rocking curves were measured of the GaAs 200 diffraction and the transmitted beams in the symmetric Laue case. The rocking curve of the transmitted beam is asymmetric with respect to the angle of the exact Bragg condition. The asymmetry reverses as the sign of the Fourier transform of either the real or the imaginary part of the X-ray polarizability changes. From the turning point of asymmetry, the accuracy of the existing calculated values of anomalous scattering factors was examined.