  Engineering single atomic defects into wide bandgap materials has become an
attractive field in recent years due to emerging applications such as
solid-state quantum bits and sensors. The simplest atomic-scale defect is the
lattice vacancy which is often a constituent part of more complex defects such
as the nitrogen-vacancy (NV) centre in diamond, therefore an understanding of
the formation mechanisms and precision engineering of vacancies is desirable.
We present a theoretical and experimental study into the ultra-fast laser
generation of vacancy-interstitial pairs (Frenkel defects) in diamond. The
process is described by a set of coupled rate equations of the pulsed laser
interaction with the material and of the non-equilibrium dynamics of charge
carriers during and in the wake of the pulse. We find that a model for Frenkel
defect generation via the recombination of a bound biexciton as the electron
plasma cools provides good agreement with experimental data, reproducing an
effective non-linearity of $\sim$ 40 for Frenkel defect generation with respect
to laser pulse energy.
