2026 Frikkin Lasers Challenge: Measuring Nanometer-Scale Displacements with an Optical Cavity

Hackaday reports that a maker named Timothy Giles has built an optical cavity from three-D-printed parts to measure displacements smaller than a wavelength of light. The setup uses two semi-transparent mirrors, with one mounted to a speaker's diaphragm—the speaker itself becomes the actuator. As the diaphragm moves, it changes how light interferes within the cavity, creating brightness patterns that a webcam captures. By counting those peaks, Giles could precisely measure microscopic movements. As a bonus, the experiment revealed an unexpected detail about the laser diode itself—during startup, its wavelength drifts as the diode warms up, visible in the same interference signatures.

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