Acoustic vortices have attracted a great deal of attention in recent years due to their numerous applications. We introduce a highly efficient method for the generation of acoustic Bessel vortices in air, using spiral-shaped active diffraction gratings, which can be operated within a broad spectral range of ultrasonic frequencies. Using a single-arm active spiral source, we achieve the simultaneous generation of vortices of different topological charges, well separated among each other along the propagation axis. With a theoretical analysis, numerical simulations, and experiments, we demonstrate some features about spiral diffraction gratings, such as the equivalence between specific diffraction orders of an m-armed spiral and a single-arm spiral, and the annihilation of prescribed diffraction orders by tuning the width to pitch ratio.

中文翻译：

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通过有源衍射光栅产生多涡旋光束

近年来，声学涡旋因其广泛的应用而引起了极大的关注。我们介绍了一种使用螺旋形有源衍射光栅在空气中产生声学贝塞尔涡旋的高效方法，该光栅可以在很宽的超声波频率范围内运行。使用单臂有源螺旋源，我们实现了同时产生不同拓扑电荷的涡流，这些涡流沿传播轴相互分离。通过理论分析、数值模拟和实验，我们证明了螺旋衍射光栅的一些特征，例如m臂螺旋和单臂螺旋的特定衍射级之间的等效性，以及通过调谐消除规定的衍射级宽间距比。