  In strong-coupling superconductors with a short electron mean free path the
self-energy effects in the superconducting order parameter play a major role in
the phonon manifestation of the point-contact spectra at the above-gap
energies. We derive asymptotic expressions of the phonon structure in
MgB$%_{2}$ in the case $eV\gg\Delta $ for tunnel, ballistic, and diffusive
point-contacts and show that these expressions not only qualitatively, but also
semi-quantitatively correspond to the measurements of the phonon structure in
the point-contact spectra for the $\pi$-band of MgB$_{2}$ c-axis oriented thin
films.

Superconductivity