A triple correlator of fluctuating photocurrents is shown to be able to analyze asymmetrical spectrum profiles of light beams, such as laser beams, without the use of an additional light source. The resolving time of photodetectors, multipliers, and electronic delay lines involved must be shorter than the coherence time of the light beam to be analyzed. The method cannot determine the mean frequency of an incident beam and cannot distinguish between a spectrum profile and its mirror image around the mean frequency.