  The threshold properties of very small lasers (down to the nanoscale) are a
topic of active research in light of continuous progress in nanofabrication.
With the help of a simple rate equation model we analyze the intrinsic,
macroscopic dynamics of threshold crossing for Class B lasers. We use the
deterministic aspects of the basic rate equations to extract some fundamental
time constants from an approximate analysis of laser dynamics in the threshold
region. Approximate solutions for the population inversion and for the field
intensity, up to the point where the latter reaches macroscopic levels, are
found and discussed. The resulting timescales characterize the laser's ability
to respond to perturbations (external modulation or intrinsic fluctuations in
the lasing transition region). Numerical verifications test the accuracy of
these solutions and confirm their validity. The predictions are used to
interpret experimental results obtained in mesoscale lasers and to speculated
about their extension to nanolasers.

Optics