Abstract: Based on the Fourier optics principle，the diffraction of a laser transmitting through a standing wave

and the imaging of that standing wave are studied. A spatial filtering experiment is designed to verify the formulas

which describes the fringe interval and contrast of the standing wave image. This method can also measure sound velocity

of the standing wave. We analyze the standing wave imaging completely and help to have a deeper understanding

of the spatial filtering method.

Key words: Fourier optics, standing wave, spatial filtering, sound velocity measurement