Low-cost quadrature optical interferometer

We report on the construction and characterization of a low-cost Mach-Zehnder optical interferometer in which quadrature signal detection is achieved by means of polarization control. The device incorporates a generic green laser pointer, home-built photodetectors, 3D-printed optical mounts, a circular polarizer extracted from a pair of 3D movie glasses, and a python-enabled microcontroller for analog-to-digital data acquisition. Components fit inside of a 12 "x 6 " space and can be assembled on a budget of less than US$500. The device has the potential to make quadrature interferometry accessible and affordable for instructors, students, and enthusiasts alike.