15 March 2016 Evaluation of Fabry-Perot polymer film sensors made using hard dielectric mirror deposition
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Fabry-Perot (FP) polymer film sensors offer high acoustic sensitivity, small element sizes, broadband frequency response and optical transmission to enable high resolution, backward mode photoacoustic (PA) imaging. Typical approaches to sensor fabrication involve the deposition of stacks of alternating dielectric materials to form interferometer mirrors, which are separated by a polymer spacer. If hygroscopic soft dielectric materials are used, a protective polymer layer is typically required. In this study, methods for the deposition of water-resistant, hard dielectric materials onto polymers were explored to improve the robustness and performance of the sensors. This involved the optimisation of the fabrication process, the optical and acoustic characterisation of the sensors, and a comparison of the frequency response with the output of an acoustic forward model. The mirrors, which were separated by a 20 μm Parylene spacer, consisted of eight double layers of Ta2O5 and SiO2 deposited onto polymer substrates using temperature-optimised electron vapour deposition. The free spectral range of the interferometer was 32 nm, its finesse FR = 91, and its visibility V = 0.72. The noise-equivalent pressure was 0.3 kPa (20 MHz bandwidth). The measured frequency response was found to be more resonant at 25 MHz compared to sensors with soft dielectric mirrors, which was also in good agreement with the output of a forward model of the sensor. The sensors were used in a PA scanner to acquire 3-D images in tissue phantoms.
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Jens Buchmann, Jens Buchmann, Edward Zhang, Edward Zhang, Chris Scharfenorth, Chris Scharfenorth, Bastian Spannekrebs, Bastian Spannekrebs, Claus Villringer, Claus Villringer, Jan Laufer, Jan Laufer, "Evaluation of Fabry-Perot polymer film sensors made using hard dielectric mirror deposition", Proc. SPIE 9708, Photons Plus Ultrasound: Imaging and Sensing 2016, 970856 (15 March 2016); doi: 10.1117/12.2234698; https://doi.org/10.1117/12.2234698

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