1E-4 Optical Generation of High Frequency Ultrasound Using a Two Dimensional Array of Gold Nanoparticles

The thermoelastic effect in a thin film is used to produce high-frequency, high-intensity ultrasound for applications in water and soft tissue. We have fabricated a structure that consists of 2D arrangements of gold nanoparticles, sandwiched between a transparent substrate and a 4.5 mum thick PDMS layer. The acoustic signal displays significant improvements compared to a bulk black PDMS film (the current state of the art) at frequencies from 50-100 MHz. When a 5 ns laser pulse with energy of 25 muJ is delivered to a spot size of 25 mum, the acoustic pressure can reach 500 kPa at a distance of 10 mm away from the film surface. We also propose a convenient method to construct an integrated transmit/receive optoacoustic array based on the high optical extinction ratio of the film. These results show that this PDMS film with 2D array of gold nanoparticles can be used to produce high-frequency arrays for ultrasound imaging