A simple interferometric technique which uses a diverging spherical comparison wave for study of laser beams is described. The interference pattern resulting from superposition of the primary beam and a small portion of the expanded comparison wavefront provides information about both the phase and some spatial coherence properties of the primary radiation. Expected interference patterns have been obtained for a spatially coherent beam from a He&sngbnd;Ne gas laser. The phase character and spatial coherence features of the beam from aQ‐switched ruby laser have been investigated.