Improvements in optical generation of high-frequency ultrasound

The thermoelastic effect in a black poly-dimethylsiloxane (PDMS) film is used to produce high-frequency, high-intensity ultrasound for applications in water and soft tissue. We show that the optoacoustic transduction efficiency is improved by about 10 dB by decreasing the thickness of the black PDMS film from 25 mum to 11 mum. The center frequency of the generated ultrasound is 60 MHz, with a -6 dB bandwidth of 80%. When a 5 ns laser pulse with energy of 50 ns is delivered to a spot size of 25 mum, the acoustic pressure 10 mm away from the film surface is about 800 kPa. Furthermore, we demonstrate that the center frequency and bandwidth of the generated ultrasound is mainly determined by the temporal profile of the input optical pulse, and it has the potential to be easily improved to above 100 MHz