Design and characterization of a highly directional photoacoustic sensor probe

We present design and comprehensive characterization of a versatile, small-scale photoacoustic sensor stick. Due to its optimized forward-looking directional characteristic, it is a valuable tool for spatially resolved PA depth scanning and 3D imaging. The pencil-formed, optical fiber-coupled sensor has a diameter of only 6 mm, with a length of 15 cm. For characterization of its fundamental parameters, we applied a pulsed frequency-doubled Nd:YAG laser (532 nm) with a pulse repetition rate of 10 Hz. Different designs of the sensor tip are compared. We present a full characterization of the qualities of the system as imaging tool, i.e. lateral and depth resolution in dependence on light absorption and scattering properties of the samples as well as of the surrounding matrix. Specially tailored phantoms are introduced for these experiments. The phantoms in combination with a xy-scanning stage are applied to produce 2D and 3D images with the sensor. The imaging properties of the endoscope are explored by several methods of characterization. We test the sensitivity to absorbing structures of different size and absorptivity, which can be summarized as contrast. Finally, we present first tomographic images of tissue phantoms resembling the optical properties of human tissue.

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