  We adapt the Quantum Monte Carlo method to the cascaded formalism of quantum
optics, allowing us to simulate the emission of photons of known energy.
Statistical processing of the photon clicks thus collected agrees with the
theory of frequency-resolved photon correlations, extending the range of
applications based on correlations of photons of prescribed energy, in
particular those of a photon-counting character. We apply the technique to
autocorrelations of photon streams from a two-level system under coherent and
incoherent pumping, including the Mollow triplet regime where we demonstrate
the direct manifestation of leapfrog processes in producing an increased rate
of two-photon emission events.
