Photoacoustic Demonstration: Making Music with Light

Abstract

In this paper, we present simple demonstrations aimed at explaining the fundamental principles of the photoacoustic effect. To display the audible phenomenon that occurs as laser radiation gets absorbed by ethene gas, an optical chopper was used to modulate the power of a continuous-wave laser whose beam was directed into a gas. The absorbed pulses of laser light resulted in time, harmonic, temperature, and pressure perturbations that excited the resonator, eliciting an acoustic response at its fundamental resonance frequency and harmonics. Multiple variables were changed to determine their effect on the photoacoustic signal and to replicate similar factors that influence the tones produced by musical instruments. Videos of the oscilloscope were recorded for various musical notes and then assembled into a combined demonstration video. This demonstration can be used to generate greater interest in the sciences as well as explain fundamental concepts that are at work in this experiment to students. The results of the student survey in General Chemistry 2 lectures show that the demonstration videos were useful resources.