  Degenerate two-photon indirect absorption in silicon is an important limiting
effect on the use of silicon structures for all-optical information processing
at telecommunication wavelengths. We perform a full band structure calculation
to investigate two-photon indirect absorption in bulk silicon, using a
pseudopotential description of the energy bands and an adiabatic bond charge
model to describe phonon dispersion and polarization. Our results agree well
with some recent experimental results. The transverse acoustic/optical
phonon-assisted processes dominate.
