Diffraction of a Helium-Neon laser beam, producing a classic case of Fresnel diffraction on an edge (also called half-infinite screen, razor blade, knife edge). A portion of a Helium-Neon laser beam is blocked and the resulting diffraction pattern is observed on a screen some distance away. Because of the diffraction, characteristic intensity ripple occurs in the area of geometric shadow (right hand side). Characteristic laser speckle pattern is apparent. The speckle results from scattering of the monochromatic beam by the screen that is rough on a microscopic (wavelength) scale.