Photoacoustic microscopy (PAM) does not rely on contrast agent to image the optical absorption contrast in biological tissue. It is uniquely suited for measuring several tissue physiological parameters, such as hemoglobin oxygen saturation, that would otherwise remain challenging. Researchers are designing new clinical diagnostic tools and multimodal microscopic systems around PAM to fully unleash its potential. However, the sizeable and opaque piezoelectric ultrasonic detectors commonly used in PAM impose a serious constraint. Our solution is a coverslip-style optically transparent ultrasound detector based on a polymeric optical micro-ring resonator (MRR) with a total thickness of 250ǎ €...I 1/4m. It enables highly-sensitive ultrasound detection over a wide receiving angle with a bandwidth of 140ǎ €...MHz, which corresponds to a photoacoustic saturation limit of 287ǎ €...cm ǎ ̂'1, at an estimated noise-equivalent pressure (NEP) of 6.8ǎ €...Pa. We also established a theoretical framework for designing and optimizing the MRR for PAM.
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