Fully planar laser-generated focused ultrasound transmitter

Abstract

Laser-generated focused ultrasound (LGFU) has been attracting great interest due to its great potential in high-resolution ultrasound imaging and high-precision therapy. However, the existing methods suffer from distinct issues such as complicated film coating control, difficult technical transfer toward device miniaturization, and limited output acoustic pressure as well as operation condition. In order to explore an effective solution for LGFU working under more universal excitation conditions with a single nanosecond pulsed laser, a new strategy based on directly patterning the flat photoacoustic (PA) source is developed in this paper. For proof of concept demonstration, a planar PA transmitter is constructed using a chromium mask with transparent rings as the substrate. Considering the broadband nature of the generated PA signal, the effects of the ring structure on focusing characteristics are explored experimentally for the first time. Besides, its capability to provide a X-wave like focused acoustic field with output pressure at MPa level and a small lateral size of several hundred micrometers yet large focal depth of a few centimeters has been successfully demonstrated, which would benefit applications requiring large ultrasound working distance. Based on the same concept, various methods can also be involved to increase its adaptability and applicability further. • A planar ring-shape photoacoustic transmitter is used for focused ultrasound. • The effects of the ring parameters on the focusing characteristics are revealed. • X-wave like focused acoustic field with extended focal depth has been demonstrated.