Vortex beam interactions for the measurement of nonlinear acoustic behaviour

Abstract

Spatially shaped optical fields have been widely implemented for remote sensing, enhanced imaging and communications. Many of these principles can be readily translated into acoustics, where acoustic fields that carry orbital angular momentum (OAM) have gained considerable interest in recent years. These spatially shaped fields can provide unique acoustic interactions with materials and gasses as they propagate that can be leveraged to create novel sensor technologies. We will present a technique to amplify the visibility of nonlinear acoustic effects in gasses, via the controlled interference of acoustic pulses that carry OAM. This amplification allows accurate determination of the nonlinear parameter with acoustic pressures that are 66dB lower than a direct measurement of pulse chirping. In controlled conditions, non-linear parameters can be directly measured; however, variations in environmental parameters can lead to ambiguity, which can be addressed through the use of a trained Support Vector Machine machine learning approach. This will allow measurements in variation in the nonlinear parameter 0.01 with over 99.5% accuracy and 0.001 with over 75% accuracy based on single measurements, where repeated measurements can further reduce the power requirements and increase accuracy. This approach can be used for monitoring changes in air quality and if extended to other frequencies could be used for monitoring fatiguing in metals.