  Using the QCD dipole picture of the BFKL pomeron, the cross-section of single
diffractive dissociation of virtual photons at high energy and large
diffractively excited masses is calculated. The calculation takes into account
the full impact-parameter phase-space and thus allows to obtain an exact value
of the triple BFKL Pomeron vertex. It appears large enough to compensate the
perturbative 6-gluon coupling factor (alpha/pi)^3 thus suggesting a rather
appreciable diffractive cross-section.
