  When the electromagnetic field is detected by stimulated emission, rather
than by absorption, antinormally ordered photodetection can be realized. One of
the distinct features of this photodetection scheme is its sensitivity to
zero-point fluctuation due to the existence of the spontaneous emission. We
have recently succeeded in experimentally demonstrating the antinormally
ordered photodetection by exploiting nondegenerate stimulated parametric
down-conversion process. To properly account for the experiment, the detection
process needs to be treated with time-dependent and continuous-mode operators
because of the broadband nature of the parametric down-conversion process and
the wide spectrum of the pump that we used. Here, we theoretically analyze the
antinormally ordered intensity correlation of the continuous-mode fields by
pursuing the detection process in the Heisenberg picture. It is shown that the
excess positive correlation due to zero-point fluctuation reduces because of
the frequency-distinguishability of the two emitted photon pairs.
