Photoacoustic Experiment using Smartphones and LEGO

The photoacoustic (PA) effect is a powerful tool for teaching integrated concepts in spectroscopy, optics, and acoustics. To overcome the high costs of traditional instrumentation, this article presents a simplified experimental setup using smartphones and LEGO® bricks. By modulating a laser to excite ethene gas, we demonstrate that a smartphone microphone paired with free Android applications can effectively detect and analyze acoustic signals. Comparative studies between glass and LEGO-built PA cells show that these accessible systems accurately reflect theoretical resonant frequencies and harmonics. Our results prove that signal intensity correlates precisely with gas concentration and cell length. This approach provides a reproducible, low-cost framework for laboratories, encouraging student engagement through familiar technology while maintaining high scientific standards.