A quasi point wave is first generated from a strongly focused laser beam and then is incident on circular apertures of different radii. By varying the distance between the aperture and the point source, one is able to observe several diffraction orders of the Fresnel diffraction on a fixed screen. With different-radius apertures in the experiment, an experimenter is able to learn the importance of a spherical wavefront in generating Fresnel diffraction.
2. Fraunhofer Diffraction
Fraunhofer diffraction is a kind of far-field diffraction and its diffraction pattern is the Fourier transform of the diffraction aperture. A series of circular and rectangular apertures are used in this experiment to verify the far-field diffraction theory. The dimensions of the apertures are deduced from the measured diffraction patterns.