  The high-intensity version of multiwavelength anomalous diffraction (MAD) has
a potential for solving the phase problem in femtosecond crystallography with
x-ray free-electron lasers (XFELs). For MAD phasing, it is required to
calculate or measure the MAD coefficients involved in the key equation, which
depend on XFEL pulse parameters. In the present work, we revisit the
generalized Karle-Hendrickson equation to clarify the importance of
configurational fluctuations of heavy atoms induced by intense x-ray pulses,
and investigate the high-intensity cases of transmission and fluorescence
measurements of samples containing heavy atoms. Based on
transmission/fluorescence and diffraction experiments with crystalline samples
of known structures, we propose an experimental procedure to determine all MAD
coefficients at high x-ray intensity, which can be used in \emph{ab initio}
phasing for unknown structures.
