Observation of two truly independent laser interference made easy

Abstract

An interference of two beams coming from one laser is a well-known and popular experiment. But is it possible to obtain interference fringes using two completely independent laser sources? If the answer is ‘yes’, is such an observation available in a typical optical laboratory? We show a simple but spectacular method of observing such an interference, using very common continuous wave He–Ne lasers as well as diode lasers often found in atomic physics laboratories. The contrast of the fringes ranges from 27% to 87%, depending on the laser properties. The method works for both single and multi-mode unstabilized He–Ne lasers. The fringes are visible on a scientific as well as on a common security camera.