First-in-human application of the optoacoustic effect

The optoacoustic effect describes the generation of sound through the absorption of laser light. When a medium absorbs laser pulses of a certain length and energy, it undergoes rapid thermal changes which can, among other effects, cause the adjacent air to expand and contract, producing sound waves. This principle offers a novel approach to auditory stimulation that may serve as an alternative to conventional acoustic stimulation used in current hearing aid technologies. To assess its feasibility, a first-in-human study was conducted with three normal-hearing participants. A multilayer absorber patch was positioned on the skin in the cavum conchae, and an 808 nm pulsed laser was used to generate tones of different sound pressure levels (27.3, 34.7, and 40.3 dB SPL) and frequencies (440, 500, 523, and 659 Hz), as well as three familiar melodies. Subjects correctly identified the order of tones by sound pressure levels with 80%–100% accuracy and by frequency with 90%–100% accuracy. All participants successfully recognized the presented melodies. Although this report is based on a limited number of individual observations and does not represent a systematic study, it nevertheless provides the worldwide first demonstration of successful optoacoustic stimulation in humans and reliable transmission of simple auditory signals via pulsed laser light.