Photoacoustic generation of intense and broadband ultrasound pulses with functionalized carbon nanotubes
Alexandre D. Silva, César A. Henriques, Daniel V. Malva, Mário J. F. Calvete, Mariette M. Pereira, Carlos Serpa, Luı́s G. Arnaut
Abstract
Carbon nanotubes (CNT) functionalized with siloxane groups were dissolved in polystyrene/tetrahydrofuran to produce thin films that generate broadband and intense ultrasound pulses when excited by pulsed lasers. These films absorb >99% of light in the visible and near-infrared and show no signs of fatigue after thousands of laser pulses. Picosecond laser pulses with fluences of 50 mJ cm-2 generate photoacoustic waves with exceptionally wide bandwidths (170 MHz at -6 dB) and peak pressures >1 MPa several millimeters away from the source. The ability to generate such broadband ultrasound pulses is assigned to the ultrafast dissipation of heat by CNT-siloxanes, and to the formation of very thin photoacoustic sources thanks to the high speed of sound of polystyrene. The wide bandwidths achieved allow for axial resolutions of 8 μm at depths less than 1 mm, similar to the resolution of histology but based on real-time non-invasive methods.