All-optical ultrasound transducer

Recent advances in fabrication techniques have accelerated development of optical generation and detection of ultrasound, a promising technology to construct high-frequency arrays for high resolution ultrasound imaging. A two-dimensional (2-D) gold nanostructure has been fabricated to optically generate high frequency ultrasound. The structure consists of 2-D arrangements of gold nanoparticles, sandwiched between a transparent substrate and a 4.5 &mgr;m thick PDMS layer. A pulsed laser beam is focused onto the optically absorbing gold nanostructure, and consequently, a localized volume is heated, and thermal expansion launches an acoustic wave into the overlying layer. The high optical extinction ratio of the gold nanostructure provides a convenient method to construct an integrated transmit/receive optoacoustic array. A thin polymer Fabry-Perot etalon is used for optoacoustic detection. The etalon is an active optical resonator, where the relatively low elasticity of the polymer and the high quality factor of the resonator combine to provide high ultrasound sensitivity. An integrated device combining the gold nanostructure and the etalon has been fabricated. Preliminary results demonstrate its promise as an all-optical ultrasound transducer.

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