We propose a novel all-optical focused ultrasound detector for intravascular optoacoustic imaging and demonstrate its imaging capabilities experimentally; the detector has a bandwidth of more than 75MHz and a spatial resolution of at least 50μm.
One of the main challenges in intravascular photoacoustic (IVPA) imaging is the limited sensitivity and bandwidth of miniaturized piezoelectric probes. Optical detectors of ultrasound can drastically improve both these features, but often lack acoustic focusing. In this work, we developed a focused ultrasound detector by integrating a miniaturized acoustic lens, made out of glass, with a silicon-photonics-based detector. A detection bandwidth of up to 80 MHz and lateral resolution beyond 50 µm was demonstrated with a lens diameter of 0.8 mm. Our device is transparent in the near-infrared window, simplifying its integration in a miniaturized IVPA probe.
Coherence-restored pulse interferometry (CRPI) is a recently developed method for optical detection of ultrasound that achieves shot-noise-limited sensitivity and high dynamic range. In principle, the wideband source employed in CRPI may enable the interrogation of multiple detectors by using wavelength multiplexing. However, the noisereduction scheme in CRPI has not been shown to be compatible with wideband operation. In this work, we introduce a new scheme for CRPI that relies on a free-space Fabry-Perot filter for noise reduction and a pulse stretcher for reducing nonlinear effects. Using our scheme, we demonstrate that shot-noise-limited detection may be achieved for a spectral band of 80 nm and powers of up to 5 mW.
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