The theory to investigate capillary waves using optical diffraction with oblique incidence is proposed.When the laser beam obliquely impinges on capillary waves at a certain angle,steady and visible diffraction patterns are observed.The diffraction intensity will change with the amplitude of capillary waves,and the missing order is formed.Furthermore,obvious asymmetry of patterns is observed.The proposed theory is derived from the theory of Fourier optics,and the capillary wave acts as a sinusoidal reflecti...