Based on the Zernike method of the zeroorder spectral phase modification a single expanded laser beam can be converted into arbitrary illuminated shape with theoretical 100% efficiency with a pair of spec ific binary phase gratings. We have obtained the relation among the phases and t he phasemodulated space factor of the aperture.Experimental demonstration of 3/4 space factor, 3×3π phasemod ulatedsquare areas with 89% efficiency is given．