Microbubble resonators for sensing and light generation applications

In this thesis microbubble resonators are studied for their implementation as optical sensors for the characterisation of photoacoustic contrast agents and as micro-cavities for the collection of the emission from single-photon sources. The first study is experimental and focuses on two experiments implementing the microbubble as an all-optical ultra-compact transducer. In particular, in the first experiment the microbubble optical resonances allow to sense the ultrasound wave produced by the contrast agent and deduce its photostability curve, both in a static and in a challenging flow-cytometry configuration. In the second experiment, instead, the microbubble resonances allow to reconstruct the contrast agent absorption spectrum by measuring the temperature shift produced in the system by the optical absorption. In prospective, the microbubble system is promising for the characterisation of novel contrast agents, the analysis of flowing samples (e.g. blood cells oxygenation, detection of venous thrombi and/or circulating tumour cells) and the measurement of absorption spectrum in biological samples. After these experiments, a feasibility study was performed to estimate the performances of the microbubble as a micro-cavity for the collection of fluorescence from single-photon sources. In particular, the coupling of the microbubble optical modes with the fluorescence of dibenzoterrylene molecules is studied and a series of collection figures-of-merit is evaluated. An unusual regime of high dephasing is also considered for the possible implementation of the system for a room temperature experiment.