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The photoacoustic technique (laser-induced acoustic waves), which is less affected by light scattering than the optical method, is based on optical absorption and the heat properties of illuminated media. Although photoacoustic techniques have been used to study tissues, only a few authors discuss the laser- induced photoacoustic source u the acoustic transmitter. This paper employs the Monte Carlo method to simulate a laser-induced acoustic transmitter in a two-layered tissue model. The shape and location of the transmitter is dependent not only on the optical parameters and heat properties of the tissue, but also on the diameter of the laser beam. A thin beam produces a cylindrical transmitter in a shallow layer of the tissue, whereas a sturdy beam tends to generate a plate-like transmitter and drive it deeply into the tissue. Studying the properties of the transmitter may provide useful insights in several respects: it may facilitate the reception of the acoustic signal, the measuring of the distribution of optical parameters, and the determination of layer thickness and the inner structure of tissues. The results of this paper also indicate that although a thin laser beam can produce a high transverse resolution in photoacoustic imaging, there may be a trade-off in imaging depth.
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