Abstract
The natural diffraction of acoustic vortex beams results in vortices whose bright core is larger than the wavelength, limiting their use for practical applications such as long-range underwater communications. In this work, we synthesize a vortex beam of sub-wavelength size at a distance beyond Rayleigh diffraction length using the nonlinear mixing of two confocal, high-frequency and detuned vortex beams of different topological charges. A helicoidal focused acoustic source with two different curvatures is used to generate a pair of finite-amplitude vortex beams. A difference-frequency component emerges due to nonlinearity. By tuning the primary beams, a low-frequency beam of integer topological charge is observed, whose distance between magnitude maxima is about 18 times smaller than its wavelength at a distance about 3 times the Rayleigh diffraction length. Subwavelength vortices of arbitrary topological charge emerge due to the spatiotemporal interference of two primary vortex beams and due to the conservation of angular momentum during nonlinear wave-mixing. This mechanism opens new venues to design directive parametric antennas for vortex transceivers or particle manipulation systems at scales well below the diffraction limit.
BibTeX citation
@inproceedings{ISNAJimenez2022,
author = {Noé Jiménez and Joao Ealo and Rubén D. Muelas-Hurtado and Aroune Duclos and Vicente Romero-García},
booktitle = {ISNA 22: 22nd International Symposium on Nonlinear Acoustics. Oxford, UK. 4-8 July},
doi = {https://doi.org/10.1121/2.0001629},
editor = {Proceedings of Meetings on Acoustics},
isbn = {ISBN: 978-84-87985-30-4},
month = {9},
organization = {University of Oxford},
pages = {045001},
publisher = {American Institute of Physics},
series = {Oral},
title = {A helicoidal parametric antenna for subwavelength vortex generation},
url = {https://asa.scitation.org/doi/10.1121/2.0001629},
volume = {48},
year = {2022}
}