Optomechanische Ultrasoonsensoren voor Fotoakoestische Beeldvorming

Photoacoustic imaging combines the deep penetration of ultrasound with the high contrast of optical imaging by converting pulsed light into sound waves. This non-invasive technique provides excellent optical contrast and deep ultrasound penetration, enabling detailed 3D molecular visualisation of optical absorption distributions in biological tissue. Traditional systems rely on bulky, high-energy pulsed lasers and piezoelectric transducers, which limit scalability, sensitivity, and miniaturisation. This work introduces optomechanical ultrasound sensors (OMUS) based on silicon photonics, featuring optical ring resonators coupled to acoustic membranes via a nanoscale air gap. Two types of OMUS sensors are investigated: single-membrane point-like detectors for 3D tomography and novel long OMUS for 2D cross-sectional imaging, offering a simpler and more scalable optical readout compared to conventional ultrasound heads. A comprehensive multiphysics model enables accurate performance predictions, showing excellent agreement with experimental results. The long OMUS device, consisting of 50 × Ø20 µm membranes with a pitch of 30 µm over an optical racetrack length of 1.5 mm, has a measured noise equivalent pressure below 0.75 mPa/√Hz up to 30 MHz. This demonstrates that the OMUS operates near the thermomechanical noise limit. The OMUS sensors show low-noise operation and broadband performance, both in laser and LED-based imaging systems. These advancements enable high-resolution, low-noise photoacoustic imaging with greater sensitivity and scalability. The long OMUS, with its elongated detection aperture, offers a significant reduction in the number of sensors required compared to single-membrane arrays, making it more cost-effective and easier to integrate at scale. These results showcase the potential of OMUS technology for non-invasive imaging applications, including the monitoring of vascular diseases, brain imaging in freely moving mice, and point-of-care diagnostics. By combining high sensitivity, scalability, and cost-effectiveness, OMUS technology holds promise for advancing both (pre)clinical research and medical diagnostics.