Field Distribution of Diffracted Laser Beam through a Finite Aperture Lens

The diffraction field of a laser beam through a finite aperture lens is investigated. The transverse and the longitudinal field distributions vary depending on the focal length and the aperture radius of the lens. The variations of the field in the Fresnel region become noticeable as the observation point approaches the lens. The theoretical and the experimental results coincide within the experimental errors when the observation point is far from the lens but the difference between them becomes salient as it comes to the lens