Acoustic, Phononic, Brillouin Light Scattering and Faraday Wave-Based Frequency Combs: Physical Foundations and Applications

Abstract

Frequency combs (FCs)—spectra containing equidistant coherent peaks—have enabled researchers and engineers to measure the frequencies of complex signals with high precision, thereby revolutionising the areas of sensing, metrology and communications and also benefiting the fundamental science. Although mostly optical FCs have found widespread applications thus far, in general FCs can be generated using waves other than light. Here, we review and summarise recent achievements in the emergent field of acoustic frequency combs (AFCs), including phononic FCs and relevant acousto-optical, Brillouin light scattering and Faraday wave-based techniques that have enabled the development of phonon lasers, quantum computers and advanced vibration sensors. In particular, our discussion is centred around potential applications of AFCs in precision measurements in various physical, chemical and biological systems in conditions where using light, and hence optical FCs, faces technical and fundamental limitations, which is, for example, the case in underwater distance measurements and biomedical imaging applications. This review article will also be of interest to readers seeking a discussion of specific theoretical aspects of different classes of AFCs. To that end, we support the mainstream discussion by the results of our original analysis and numerical simulations that can be used to design the spectra of AFCs generated using oscillations of gas bubbles in liquids, vibrations of liquid drops and plasmonic enhancement of Brillouin light scattering in metal nanostructures. We also discuss the application of non-toxic room-temperature liquid–metal alloys in the field of AFC generation.

Biomechanical Sensing Using Gas Bubbles Oscillations in Liquids and Adjacent Technologies: Theory and Practical Applications

“…Since viscous forces acting in the fluid near the wall are neglected, one can use the potential flow theory to replace the wall with an identical ‘mirror’ bubble image that is located symmetrically with respect to the rigid wall and oscillates with the same frequency, amplitude, and phase as the original bubble [ 71 , 83 ]. Even though in reality Bjerknes forces could cause the distance between the bubble centre and the wall vary [ 67 , 85 , 86 , 87 ] (see also Section 2.3 ), for simplicity it is often assumed that it remains constant ( Figure 5 ). The corresponding equation is know as Keller-Miksis-Parlitz equation [ 65 , 83 ].…”

“…For a review of the recent developments in the emergent field of acoustic frequency combs (AFCs) readers are referred to [ 87 ]. Here, we first describe an important class of AFCs based on the oscillations of acoustically-driven bubbles in liquids and then discuss their potential applications in the field of biosensing.…”

“…In [ 86 ], an alternative strategy for broadening spectra of AFCs generated using bubble oscillations was suggested. The question of long-term stability of AFC signals was comprehensively addressed (see also [ 87 ]). In [ 86 ], polydisperse clusters consisting of mm-sized bubbles with equilibrium radii were used, where is the equilibrium radius of the largest bubble in the cluster and is the total number of bubbles.…”

“…OFCs are widely used in the field of spectroscopy [ 87 , 175 , 187 , 188 ], where they both optically excite and interrogate a sample under study ( Figure 14 a). The spectral response of a sample, which may arise due to linear or nonlinear absorption of light specific to the sample’s molecular composition, may span the entire OFC spectrum.…”

“…The physical properties of Faraday waves also present significant interest for biosensing applications. Interested readers are referred to a recent review [ 87 ] that discusses this topic in more detail.…”