  A Stochastic Simulator (SS) is proposed, based on a semiclassical description
of the radiation-matter interaction, to obtain an efficient description of the
lasing transition for devices ranging from the nanolaser to the traditional
"macroscopic" laser. Steady-state predictions obtained with the SS agree both
with more traditional laser modeling and with the description of phase
transitions in small-sized systems, and provide additional information on
fluctuations. Dynamical information can easily be obtained, with good computing
time efficiency, which convincingly highlights the role of fluctuations at
threshold.
