Photoacoustic Technologies beyond Medical Imaging–PASA and LGFU
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Photoacoustic (PA) effect has been extensively studied as a direct and efficient light-to-sound conversion mechanism. This dissertation is aimed to explore the possibilities of applying photoacoustic effects in fields beyond medical imaging, including non-imaging analysis, therapeutic treatment and nozzle-free jetting printing towards flexible electronics. On one hand, we have found a solid relationship between the morphological characteristics of PA generators and the spectrum of the PA signals, which is referred to photoacoustic spectrum analysis (PASA). By implementing an ultra-broad-bandwidth ultrasound detector"”microring, we are able to characterize the size and shape of bio-samples in cellular size fast and accurate, which has been demonstrated for blood freshness determination. On the other hand, we developed photoacoustic way for ultrasound focusing called laser-generated-focused-ultrasound (LFGU) with lab-developed PA lens, made from cheap and simple-fabricated candle soot/PDMS composite. A tightly focused pressure field within an ellipsoid with 90um (minor axis) * 200um (major axis) has been achieved. The induced cavitation bubbles release large mechanical energy to be applied in both ablation of bio-tissues and generation of thin(~10µm) and high-speed streams. The former provides a non-invasive way for precise Acne treatment, and we have demonstrated the ablation effect in vitro on sectioned human skin and ex vivo on mouse whole ear and pork skin sample. The latter provides a nozzle-free jet printing method that has been demonstrated to print 2D materials such as graphene and MoS2 with ~200µm resolution.