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 generates a pair of finite-amplitude vortex beams. Nonlinearity generates a low-frequency focused vortex beam, of integer topological charge, whose distance between magnitude maxima is about 18 times smaller than its wavelength at a distance about 3 times the Rayleigh diffraction length. Sub-wavelength vortices 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{JimenezEaloMuelas-HurtadoEtAl2021,
author = {Noé Jiménez and Joao Ealo and Rubén D. Muelas-Hurtado and Aroune Duclos and Vicent Romero-García},
booktitle = {EuroNoise 2021: European Congress and Exposition on Noise Control Engineering. Madeira, Portugal. 24-27 October},
doi = {http://www.sea-acustica.es/},
editor = {Conference proceedings},
month = {10},
organization = {Sociedade Portuguesa de Acústica},
pages = {316-320},
series = {Oral},
title = {Parametric generation of subwavelength acoustic vortices},
url = {http://www.sea-acustica.es/},
year = {2021}
}