Acoustic helical dichroism (HD) is a fascinating phenomenon that occurs when vortex beams carrying orbital angular momentum (OAM) interact with chiral media. However, these chiral sound-matter interactions are often weak, limiting their potential applications. In a recent study, researchers Qing Tong, Tong Fu, Yuqiong Cheng, and Shubo Wang have found a way to enhance acoustic HD using a novel approach involving quasi-bound states in the continuum (QBICs) in acoustic meta-cavities.
The team designed both achiral and chiral meta-cavities composed of coupled Helmholtz resonators that support QBICs in the form of vortex states with high Q-factors. Using full-wave numerical simulations, they demonstrated that the QBICs in the achiral meta-cavities cannot enhance acoustic HD due to the absence of a chiral wavefront. However, the chiral meta-cavity exhibited a pronounced HD enhancement through the QBICs with a 3D helical wavefront, which can be excited by incident waves either with or without OAM.
The researchers identified two essential requirements for enhancing the acoustic HD effect via QBICs: a high Q-factor of the states and 3D chirality of the state fields. These two factors usually compromise each other in conventional acoustic resonators, making the team’s findings particularly significant.
The implications of this research are far-reaching. By achieving strong chiral sound-matter interactions, we could see advancements in acoustic chiral sensing and acoustic OAM manipulation. This could lead to new applications in fields such as medical imaging, non-destructive testing, and communication technologies. The team’s innovative approach to enhancing acoustic HD opens up new avenues for exploration and could pave the way for exciting developments in the field of acoustics.
