A tabletop experiment for speed of light measurement using a Red Pitaya STEMlab board

Abstract

The speed of light is an important fundamental constant in physics, and so determining its value is a common undergraduate laboratory experiment. Methods to measure the light speed can help students practice their experimental skills and become familiar with the concepts of modern precision measurement techniques. In this paper, we demonstrate that a tabletop optical setup, comprised of an affordable Red Pitaya STEMlab board and a low-cost laser diode module, can be used to accurately determine the speed of light by measuring the frequency response of the phase shift between intensity-modulated light beams reflected by two end mirrors separated by 50 cm. By using the STEMlab built-in Bode analyzer to automatically scan the modulation frequency over the range from 10 to 40 MHz, the frequency response of phase is measured and recorded. These phase shift data are then used to calculate the speed of light with an uncertainty of less than 0.5%. With the help of the Red Pitaya board, the number of required electronic instruments for our setup is reduced. All of the required components are commercially available, and no electronic construction work is necessary so that teachers and students can implement the experiment in a plug-and-play manner.