@inproceedings{BuchmannZhangScharfenorthetal.2016, author = {Buchmann, Jens and Zhang, Edward and Scharfenorth, Chris and Spannekrebs, Bastian and Villringer, Claus and Laufer, Jan}, title = {Evaluation of Fabry-Perot polymer film sensors made using hard dielectric mirror deposition}, publisher = {Society of Photo-Optical Instrumentation Engineers (SPIE)}, url = {http://nbn-resolving.de/urn:nbn:de:kobv:526-opus4-15289}, pages = {920 -- 928}, year = {2016}, abstract = {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.}, language = {en} } @inproceedings{GilaniVillringerZhangetal.2018, author = {Gilani, Taravat Saeb and Villringer, Claus and Zhang, Edward and Gundlach, H. and Buchmann, Jens and Schrader, Sigurd and Laufer, Jan}, title = {Parallelised photoacoustic signal acquisition using a Fabry-Perot sensor and a camera-based interrogation scheme}, publisher = {SPIE}, url = {http://nbn-resolving.de/urn:nbn:de:kobv:526-opus4-15335}, pages = {217 -- 222}, year = {2018}, abstract = {Tomographic photoacoustic (PA) images acquired using a Fabry-Perot (FP) based scanner offer high resolution and image fidelity but can result in long acquisition times due to the need for raster scanning. To reduce the acquisition times, a parallelised camera-based PA signal detection scheme is developed. The scheme is based on using a sCMOScamera and FPI sensors with high homogeneity of optical thickness. PA signals were acquired using the camera-based setup and the signal to noise ratio (SNR) was measured. A comparison of the SNR of PA signal detected using 1) a photodiode in a conventional raster scanning detection scheme and 2) a sCMOS camera in parallelised detection scheme is made. The results show that the parallelised interrogation scheme has the potential to provide high speed PA imaging.}, language = {en} } @inproceedings{VillringerGilaniZhangetal.2019, author = {Villringer, Claus and Gilani, Taravat Saeb and Zhang, Edward and Pulwer, Silvio and Steglich, Patrick and Schrader, Sigurd and Laufer, Jan}, title = {Development of tuneable Fabry-P{\´e}rot sensors for parallelised photoacoustic signal acquisition}, series = {Proc. SPIE 10878, Photons Plus Ultrasound: Imaging and Sensing 2019, 108780M (8 March 2019)}, booktitle = {Proc. SPIE 10878, Photons Plus Ultrasound: Imaging and Sensing 2019, 108780M (8 March 2019)}, publisher = {Society of Photo-Optical Instrumentation Engineers (SPIE)}, issn = {1996-756X}, url = {http://nbn-resolving.de/urn:nbn:de:kobv:526-opus4-13769}, year = {2019}, abstract = {Fabry-P{\´e}rot (FP) sensors have enabled high resolution 3D photoacoustic (PA) imaging in backward mode. However, raster-scanning of the interrogation laser beam across the sensor can result in slow 3D image acquisition. To overcome this limitation, parallelized PA signal acquisition can be used for which FP sensors with uniform optical thickness are required. In this work, the optical thickness is tuned a) irreversibly through the use of a photopolymer host matrix and b) actively using embedded electro-optic (EO) chromophores. Polymer spacers (5 μm) were deposited using spin coating and sandwiched between two dielectric mirrors and transparent ITO electrodes. The employed polymer guest-host system consists of an EO chromophore (2-methyl-4-nitroaniline) and poly(vinyl cinnamate). EO tuneability was induced using contact poling and a tuneability of 68 pm was demonstrated. The optical thickness was homogenised by raster scanning a UV beam whilst varying the exposure time across a 4 mm2 detection aperture.}, language = {en} } @article{BaumannPohleZhangetal.2021, author = {Baumann, Elisabeth and Pohle, Ulrike and Zhang, Edward and Allen, Thomas and Villringer, Claus and Pulwer, Silvio and Gerhardt, Holger and Laufer, Jan}, title = {A backward-mode optical-resolution photoacoustic microscope for 3D imaging using a planar Fabry-P{\´e}rot sensor}, series = {Photoacoustics}, volume = {24}, journal = {Photoacoustics}, publisher = {Elsevier}, issn = {2213-5979}, url = {http://nbn-resolving.de/urn:nbn:de:kobv:526-opus4-14701}, pages = {100293}, year = {2021}, abstract = {Optical-resolution photoacoustic microscopy (OR-PAM) combines high spatial resolution and strong absorption-based contrast in tissue, which has enabled structural and spectroscopic imaging of endogenous chromophores, primarily hemoglobin. Conventional piezoelectric ultrasound transducers are typically placed far away from the photoacoustic source due to their opacity, which reduces acoustic sensitivity. Optical ultrasound sensors are an alternative as their transparency allows them to be positioned close to the sample with minimal source-detector distances. In this work, a backward-mode OR-PAM system based on a planar Fabry-P{\´e}rot ultrasound sensor and coaxially aligned excitation and interrogation beams was developed. Two 3D imaging modes, using raster-scanning for enhanced image quality and continuous-scanning for fast imaging, were implemented and tested on a leaf skeleton phantom. In fast imaging mode, a scan-rate of 100,000 A-lines/s was achieved. 3D images of a zebrafish embryo were acquired in vivo in raster-scanning mode. The transparency of the FP sensor in the visible and near-infrared wavelength region makes it suitable for combined functional and molecular imaging applications using OR-PAM and multi-photon fluorescence microscopy.}, language = {en} } @inproceedings{PohleBaumannPulweretal.2019, author = {Pohle, Ulrike and Baumann, Elisabeth and Pulwer, Silvio and Villringer, Claus and Zhang, Edward and Gerhardt, Holger and Laufer, Jan}, title = {Development of a backward-mode photoacoustic microscope using a Fabry-P{\´e}rot sensor}, publisher = {SPIE}, url = {http://nbn-resolving.de/urn:nbn:de:kobv:526-opus4-15349}, pages = {594 -- 598}, year = {2019}, abstract = {Optical-resolution photoacoustic microscopy (PAM) has been shown to enable the acquisition of high resolution (μm) functional and anatomical images. For backward-mode operation, conventional piezoelectric ultrasound transducers need to be placed far away from the signal source due to their opacity and size. This can result in reduced acoustic sensitivity. Planar Fabry-Perot polymer film interferometer (FPI) sensors have the potential to overcome this limitation since they are transparent to the excitation wavelength, can be placed immediately adjacent to the signal source for high acoustic sensitivity, and offer a broadband frequency response (0 -50 MHz). In this study, we present a high frame rate, backward-mode OR-PAM system based on a planar FPI ultrasound sensor. A ns-pulsed laser provides excitation pulses (<200 nJ, maximum pulse repetition frequency = 200 kHz, 532 nm) to generate photoacoustic waves that are detected using a planar FPI sensor interrogated at 765-781 nm. For backwardmode operation and highest acoustic sensitivity, the excitation and interrogation beams are coaxially aligned and rasterscanned. The optical transfer function of the sensor, the spatial resolution and the detection sensitivity were determined to characterise the set-up. Images of a leaf phantom and first in vivo images of zebrafish larvae were acquired. This approach will enable fast 3D OR-PAM with high resolution and high sensitivity for functional and molecular imaging applications. FPI-based ultrasound detection also has the potential to enable dual-mode optical- and acousticresolution PAM and the integration of photoacoustic imaging with purely optical modalities such as multi-photon microscopy.}, language = {en} }