Simple Optical System for Fraunhofer Diffraction Experiments

Abstract

When an aperture (or obstacle) is placed within the cross section of a beam of light and the transmitted light is observed on a screen, the resulting distribution of light is called a diffraction pattern. There are two basic forms of diffraction: Fresnel and Fraunhofer. If both source and observation screen are at a finite distance from the diffracting object, the pattern is called a Fresnel diffraction pattern (near-field diffraction). Under these conditions an image of the aperture (or obstacle) is projected onto the observation screen. The image is clearly recognizable despite some fringing around its periphery. If the observation screen is placed very far from the diffracting object, the pattern is called a Fraunhofer diffraction pattern (far-field diffraction). At a very great distance the projected pattern will bear little or no resemblance to the diffracting object. Moving the observation screen even further away will only change the size of the pattern but not its shape.