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Control of Broadband Optically Generated Ultrasound Pulses Using Binary Amplitude Holograms

BROWN Michael D., JAROŠ Jiří, COX Ben T. and TREEBY Bradley E. Control of Broadband Optically Generated Ultrasound Pulses Using Binary Amplitude Holograms. The Journal of the Acoustical Society of America, vol. 139, no. 4, pp. 1637-1647. ISSN 1520-8524. Available from: http://scitation.aip.org/content/asa/journal/jasa/139/4/10.1121/1.4944758
Czech title
Generování ultrazvuku pomocí laseru
journal article
Brown Michael D. (UCL)
Jaroš Jiří, doc. Ing., Ph.D. (DCSY FIT BUT)
Cox Ben T. (UCL)
Treeby Bradley E. (UCL)
ultrasound, photoacoustic , spectral methods, k-Wave
Optical generation of ultrasound with the photoacoustic effect is a promising alternative to piezoelectric transducers for certain biomedical applications of ultrasound including particle manipulation and high frequency imaging. It has been shown previously that precise control over the spatial distribution of pressure in optically generated acoustic fields is possible using patterned optical excitations and spectrally controlled acoustic pulses. However, the acoustic pressures achieved with this technique have been limited. In this work, the use of binary amplitude holography is investigated as a mechanism to focus broadband acoustic pulses generated by high peak-power pulsed lasers. Two algorithms are described for the calculation of the binary holograms; one using ray-tracing, and one using an optimisation based on direct binary search. It is shown using numerical simulations that when a binary amplitude hologram is excited by a train of laser pulses at its design frequency, the acoustic field can be focused at a pre-determined distribution of points, including single and multiple focal points, and line and square foci. For acoustic fields with a single focus it is shown the number of pulses needed for the volume of the focus to reach steady state is dependent on the aperture size, that two pulses are suffcient to form an axial focus, and that the focus depth can be steered by varying the pulsing frequency. The numerical results are validated by acoustic field measurements from binary amplitude holograms fabricated by laser cutting, excited by a high peak-power laser.
The Journal of the Acoustical Society of America, vol. 139, no. 4, ISSN 1520-8524
American Institute of Physics for the Acoustical Society of America
   author = "D. Michael Brown and Ji\v{r}\'{i} Jaro\v{s} and T. Ben Cox and E. Bradley Treeby",
   title = "Control of Broadband Optically Generated Ultrasound Pulses Using Binary Amplitude Holograms",
   pages = "1637--1647",
   journal = "The Journal of the Acoustical Society of America",
   volume = 139,
   number = 4,
   year = 2016,
   ISSN = "1520-8524",
   doi = "10.1121/1.4944758",
   language = "english",
   url = "https://www.fit.vut.cz/research/publication/10973"
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