Visualization of an acoustic stationary wave by optical feedback interferometry

© 2018 Society of Photo-Optical Instrumentation Engineers (SPIE). This paper presents an experimental technique for two-dimensional imaging of dynamic acoustic pressure changes that is applied to visualize a stationary acoustic wave. This technique uses the optical feedback interferometry sensing scheme with a near-infrared laser diode and a two-axis scanning system. The stationary acoustic wave is generated by using a 40 kHz piezoelectric transducer pointing toward a concave acoustic reflector. The acoustic pressure dynamic changes are measured due to its impact on the propagating medium refractive index, which variation is integrated along the laser optical path from the laser diode to a distant mirror and back. The imaging system records a 100×50 pixels image of the acoustic pressure in 66 min.