J. Eur. Opt. Society-Rapid Publ. 21, 26( 2025) 271
Figure
34. A series of WGMR-based magnetometers.( a) microtoroid with a microsized magnet encapsulated using poly( dimethylsiloxane),( b) microtoroid with an embedded Terfenol-D cylinder,( c) microtoroid with a thin film of Terfenol-D sputter coated on top,( d) a mm-size CaF 2 microdisk resonator with a cylinder of Terfenol-D embedded inside. Adapted from [ 71 ].
Figure
35. Left: sketch of the experimental setup used to demonstrate PA detection through a microbubble resonator. Right: PA response against excitation fluence measured through the MBR transducer for a GNRs colloidal solution.
In these works, it has been demonstrated that the mechanical spectrum can be exploited as a filter to reduce the environmental noise. In addition, the extremely small volume, the direct implementation and the absence of an acoustic impedance-matching material are promising elements for wearable appliances and / or an endoscope. The applicability range of the MBR transducer extends beyond the medical area: in particular, applications in biology, material science and chemistry could benefit from its features. For example, the transducer could be used as a compact biosensor or as a gauge for development of new contrast agents. Additionally, the MBR would allow to interrogate the hosted material with an high repetition rate, ultimately limited by the decay time of the MBR mechanical modes. For the system here presented this limit is close
Figure 36.( a) Sketch of the experimental setup. MR: mirror, AL: aspherical lens, PD: photodiode, Pol. Con.: polarisation controller.( b) Power-normalized optical shifts for an aqueous solution containing GNRs( 1.5 mM Au) and milk powder( 1 % w / w)( dots). The crosses refer to a solution with only the milk powder.( c) Same shift profiles normalized to their 740 nm values, together with a reference profile from a spectrophotometer( cyan curve).
to 40 kHz and would allow, for example, to track the evolution of a chemical reaction with a 25 ls time step by measuring the PA response of one reagent( e. g., growth of GNR, oxidation of the heme group).