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15 March 2016 High energy laser pulse coupling in a multimode fiber for photoacoustic tomography
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In traditional photoacoustic tomography, external illumination is used to excite acoustic waves. However, with the assistance of fibre-transmitted light, multidirectional illumination or internal illumination can be achieved which can obtain a better image at a deeper depth. Laser pulses delivered by fibre are energy-limited by the fibre core size and damage threshold. To increase the amplitude of photoacoustic waves and their penetration, it is necessary to improve the fibre coupling energy and efficiency. To improve the coupling performance of single fibres, we use a cylindrical lens array to homogenize the incident beam before a coupling lens. Simulation in Zemax shows that this approach flattens the beam profile on the front surface of the fibre, decreasing the risk of fibre damage. Experimental results with fibre core diameters of 1mm and 1.5mm show that both types of fibre can output more than 50mJ energy per pulse at 700nm wavelength. The coupling efficiency is measured to be above 70% and even reaches 90% as the wavelength changes from 675nm to 900nm. This improvement of coupling energy in single fibres will benefit photoacoustic tomography applications using internal illumination.
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Min Ai, Weihang Shu, Tim Salcudean, Robert Rohling, Purang Abolmaesumi, and Shuo Tang "High energy laser pulse coupling in a multimode fiber for photoacoustic tomography", Proc. SPIE 9708, Photons Plus Ultrasound: Imaging and Sensing 2016, 97084H (15 March 2016);

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