Observation and verification of the Fresnel and Arago interference laws using adaptive photodetectors

The Fresnel and Arago interference laws relate the polarization of the electromagnetic field to the interference phenomenon. Different methods and interferometers have been reported to verify these laws; most of them rely on visual inspection to determine the positions of maximum and minimum interference. In this report, the observation and verification of the Fresnel and Arago interference laws using adaptive photodetectors are presented. These photodetectors generate an electrical current proportional to the square of the visibility of the interference pattern; thus the gradual change from the appearance of the interference pattern (maximum visibility) to its disappearance (minimum or null visibility) is detected as an electrical current. The extreme values of the interference pattern visibility can be accurately assessed, in real time and without any signal processing using. A difference of 3 orders of magnitude between the signals measured in the positions of maximum and minimum interference is demonstrated. Due to the adaptive properties of the adaptive photodetectors (compensation of the irregularities of the interfering beams and suppression environmental fluctuations), the proposed method can be suitable for teaching purposes in undergraduate laboratories.