Abstract
In order to combine sensitive optical detection with acoustic focusing in a compact device, we propose in this work the idea of large area optical ultrasound detection, utilizing the integrating effect of a probe laser beam propagating in a plane for enhanced interaction with the acoustic field. The key component of the setup is the sensor head consisting of an acoustic lens mounted on a glass cube. Two opposite side faces of the cube are coated with a reflective metal layer except a small stripe at the edges of the cube that enables the probe beam to enter and exit the interaction zone for ultrasound detection. An obliquely incident probe beam crosses the cube along a zigzag path, thereby increasing the interaction length compared to single-pass detection. Recorded signals are proportional to the beam deflection caused by acoustically generated pressure gradients in the glass cube. With the proposed detection approach a 5 MHz detection bandwidth, a lateral spatial resolution of 330 µm and an 8-times increased signal strength was observed compared to single pass detection without folded probe beam propagation. Although the proposed free beam detection setup cannot keep up with the performance of commonly used AR-PAM systems based on piezoelectric ultrasound detection, the idea of large area optical ultrasound detection equipped with an acoustic lens has high potential. For instance, it should be possible to transfer this idea to integrated optics equipped with an acoustic lens.
© 2019 SPIE/OSA
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