Plano-convex optical microresonator detectors have been developed as an alternative to planar Fabry-Pérot (FP) sensors used in all-optical photoacoustic imaging systems with the potential to provide two or more orders-of-magnitude higher detection sensitivity. This study further characterises the performance of these detectors by investigating their normal incidence frequency response and frequency-dependent directivity. It is shown that sensors with thicknesses in the range ~50-320μm provide broadband, smooth frequency response characteristics and low directional sensitivity. This suggests that a photoacoustic imaging system based on microresonator detectors may be capable of imaging with similar performance to the FP system but with significantly higher sensitivity, paving the way to deep tissue imaging applications such as the clinical assessment of breast cancer and preclinical whole body small animal imaging.
We present novel concave Fabry Perot (FP) sensor arrays for photoacoustic imaging which were fabricated using a high-precision inkjet printing approach to produce the cavity and employed physical vapor deposition to form the dielectric mirrors. Our concave FP cavity design provides excellent beam confinement within the cavity enabling high finesse and thus high sensitivity to be achieved. Two such concave sensors are evaluated in terms of their sensitivity and acoustic bandwidth. A 66 μm thick concave sensor is shown to provide a noise equivalent pressure (NEP) of 85 Pa and an acoustic bandwidth of 16 MHz, and can potentially be used as a sensitive broadband sensor for superficial imaging. A 250 μm thick sensor with an NEP of 12 Pa and acoustic bandwidth of 4 MHz was also developed for deep tissue imaging applications.