Characterizing Laser-induced Acoustic Signals Based on Thermal Expansion Mechanism: Simulation Studies and Experiment Verifications

The paper elaborates the principle of the interaction between laser and water, and further explores the design of air-to-underwater (A2U) communication systems, all corroborated by extensive experiment results. Based on the theory of laser-excited planar sound source under the thermal expansion mechanism, a laser sound generation system was designed, from which the laser sound signals were acquired and measured. In particular, the sound signals generated under different laser conditions were compared and analyzed. Each optoacoustic signal induced in the experiment has a wide frequency band, relatively dispersed energy, and the spectral energy center is in tens of kHz, which makes it not suitable for long-distance underwater transmission. To tackle this challenge, this paper makes the attempt to utilize the re-frequency method to modulate the laser-induced acoustic signal, showing a glimmer of hope of adopting laser-induced acoustic signals in underwater applications.