An indispensable modified screen to assist automated optical fringe counting

In this article, we describe a simple experimental proposal for a modified screen to assist automated fringe counting in laser interferometry experiments. We choose a Michelson interferometer (MI) as our model experiment that has been reported in the literature (PHYWE Systeme GmbH & Co. KG 2017 Catalogue: Physics & Applied Sciences University Experiments (Michelson interferometer, item number: P2220500), ) and frequently practiced in the laboratory. The calculation of wavelength by exploiting MI requires a tedious manual method of counting fringes with the naked eye, which causes error in the measured wavelength. This error is elegantly avoided with the proposed screen, which has a small needle-sized hole at its center for the passage of light. It is also equipped with a digital fringe counter (using an ordinary calculator) combined with a photodiode (used as an optical sensor) installed at the rear side of the screen directly beneath the central hole. In principle, every time the central bright circular fringe falling on the screen replaces the dark one, the change is efficiently sensed by the photodiode, which sends a pulse to the calculator that will cause it to show an increment in its display. Our results show greater accuracy of measurement using the proposed fringe counter as opposed to the tedious traditional method. These results strongly recommend that a stand-alone digital screen with in-built light sensor and counting display is adopted and manufacturers (for example, PHYWE Systeme GmbH & Co. KG, PHYWE webpage ()) should include it in their MI setups. To the best of our knowledge, this paper is the first to propose this kind of digital screen. Finally, in this modern age of electronics, the proposal will be a vital addition to all physics laboratory experiments that involve the concepts of fringes, optics, laser interferometry, interference and electronics.