Interference between two laser beams, as could be observed using Michelson interferometer with a red Helium-Neon laser. Single laser beam is split into two beams which are then recombined and crossed at a small angle to each other. The interference fringes are observed in a plane perpendicular to the beams' propagation direction. Conceptually, this is a modern-day replication of Thomas Young's double-slit experiment. Apparent laser speckle results from scattering of the monochromatic beam by the screen that is rough on a microscopic (wavelength) scale.