Measurement of electromagnetic radiation force using a capacitance interferometer

Interferometry forms the cornerstone of several high-precision sensing techniques in physics. We present a mechanical cantilever-based tabletop interferometer to measure the force exerted by light from a pulsed laser beam. The experiment uses the interference of two sinusoidal voltage signals passing through nominally similar dielectrics formed by two cantilever-based air capacitors on a PCB. The radiation force exerted by a pulsed laser beam on one of the air capacitors causes a change in its capacitance, which is measured as a proportional change in the interfering voltage signal. This experiment uses equipment commonly found in an undergraduate teaching laboratory for physics and electronics while providing excellent insight into electromagnetic wave theory, circuit design for low-noise measurements, Fourier analysis, and interpretation of experimental data.