We derive the photocount statistics of the radiation emitted from a chaotic
laser resonator in the regime of single-mode lasing. Random spatial variat
ions of the resonator eigenfunctions lead to strong mode-to-mode fluctuatio
ns of the laser emission. The distribution of the mean photocount over art
ensemble of modes changes qualitatively at the lasing transition, and displ
ays up to three peaks above the lasing threshold.