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All-optical highly sensitive broadband ultrasound sensor without any deformable parts for photoacoustic imaging

We present a novel akinetic optical ultrasound sensor, consisting of a rigid, fiber-coupled Fabry-P´erot interferometer (FPI) with a central opening. The sensing principle relies exclusively on the detection of pressure-induced changes of the refractive index in the liquid located between the cavity mirrors. This enables resonance-free, inherently linear signal detection over a large bandwidth. We demonstrate that the sensor allows to realize exceedingly low noise equivalent pressure (NEP) values of 2 Pa over a 20 MHz measurement bandwidth, while maintaining a large full field of view of 2,7mm × 1,3mm as well as a flat frequency response. Imaging tests on phantoms and biological tissue show the suitability of the XARION-sensor for optical resolution photoacoustic microscopy (OR-PAM) applications. Transparent in axial direction, the sensor facilitates the implementation of highly sensitive fast-scanning reflection-mode OR-PAM setups, as well as easy integration with other imaging modalities such as confocal microscopy or OCT.