TY - CHAP A1 - Sievers, Jan A1 - Villringer, Claus A1 - Lebek, Werner A1 - Gilani, Taravat Saeb A1 - Laufer, Jan T1 - Photoacoustic tomography using a Fabry-Perot sensor with homogeneous optical thickness and wide-field camera-based detection T2 - Opto-Acoustic Methods and Applications in Biophotonics VI N2 - Fabry-Perot (FP) sensors are typically read out using a raster scan to acquire tomographic Photoacoustic (PA) images. To speed up the recording time, wide-field illumination of the sensor in combination with a camera as detector can be used. In this study, an sCMOS camera and wavelengths around 517 nm are used to interrogate a FP sensor with a homogeneous optical thickness over a 4 cm2 aperture. The recorded time series show PA signals are acquired over the entire area of the interrogation beam. The performance of the system, such as the noise equivalent pressure, is evaluated. KW - photoacoustic tomograph KW - Fabry-Perot sensor KW - camera-based setup KW - photopolymer KW - polyvinyl cinnamate KW - interferometer transfer function KW - acoustic sensitivity KW - detection aperture Y1 - 2023 U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:kobv:526-opus4-17850 ER - TY - CHAP A1 - Villringer, Claus A1 - Gilani, Taravat Saeb A1 - Zhang, Edward A1 - Pulwer, Silvio A1 - Steglich, Patrick A1 - Schrader, Sigurd A1 - Laufer, Jan T1 - Development of tuneable Fabry-Pérot sensors for parallelised photoacoustic signal acquisition T2 - Proc. SPIE 10878, Photons Plus Ultrasound: Imaging and Sensing 2019, 108780M (8 March 2019) N2 - Fabry-Pérot (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. Y1 - 2019 U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:kobv:526-opus4-13769 SN - 1996-756X ER - TY - CHAP A1 - Gilani, Taravat Saeb A1 - Villringer, Claus A1 - Zhang, Edward A1 - Gundlach, H. A1 - Buchmann, Jens A1 - Schrader, Sigurd A1 - Laufer, Jan T1 - Parallelised photoacoustic signal acquisition using a Fabry-Perot sensor and a camera-based interrogation scheme N2 - 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. KW - photoacoustic imaging KW - parallelised signal acquisition KW - Fabry-Perot polymer film sensor Y1 - 2018 U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:kobv:526-opus4-15335 SP - 217 EP - 222 PB - SPIE ER - TY - CHAP A1 - Pohle, Ulrike A1 - Baumann, Elisabeth A1 - Pulwer, Silvio A1 - Villringer, Claus A1 - Zhang, Edward A1 - Gerhardt, Holger A1 - Laufer, Jan T1 - Development of a backward-mode photoacoustic microscope using a Fabry-Pérot sensor N2 - 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. KW - optical-resolution photoacoustic microscopy KW - Fabry-Perot ultrasound sensor KW - in vivo imaging Y1 - 2019 U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:kobv:526-opus4-15349 SP - 594 EP - 598 PB - SPIE ER - TY - CHAP A1 - Buchmann, Jens A1 - Zhang, Edward A1 - Scharfenorth, Chris A1 - Spannekrebs, Bastian A1 - Villringer, Claus A1 - Laufer, Jan T1 - Evaluation of Fabry-Perot polymer film sensors made using hard dielectric mirror deposition N2 - 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. KW - Fabry-Perot KW - ultrasound KW - photoacoustic KW - imaging KW - sensor Y1 - 2016 U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:kobv:526-opus4-15289 SP - 920 EP - 928 PB - Society of Photo-Optical Instrumentation Engineers (SPIE) ER - TY - CHAP A1 - Kirchner, Thomas A1 - Villringer, Claus A1 - Gutke, Marko A1 - Laufer, Jan T1 - Plano-concave optical sensor for transcranial photoacoustic measurements T2 - Opto-Acoustic Methods and Applications in Biophotonics VI N2 - Biomedical photoacoustics is usually used to image absorption-based contrast in soft tissues up to depths of several centimeters and with sub-millimeter resolution. By contrast, measuring Photoacoustic (PA) signals through hard bone tissue shows severe signal degradation due to aberration and high attenuation of high frequency acoustic signal components. This is particularly noticeable when measuring through thicker, human, skull bone. Which is the main reason why transcranial PA imaging in humans has so far proved challenging to implement. To tackle this challenge, we developed an optical resonator sensor based on a previous planar-concave design. This sensor was found to be highly suitable for measuring the low-pressure amplitude and low acoustic frequency signals that are transmitted through human cranial bone. A plano-concave optical resonator sensor was fabricated to provide high sensitivity in the acoustic frequency range of DC to around 2 MHz, a low noise equivalent pressure and a small active element size enabling it to significantly outperform conventional piezoelectric transducers when measuring PA waves transmitted through ex vivo human cranial bones. KW - transcranial KW - ex vivo KW - human KW - brain KW - optical resonator KW - photoacoustic KW - optoacoustic Y1 - 2023 U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:kobv:526-opus4-17840 PB - Society of Photo-Optical Instrumentation Engineers (SPIE) ER - TY - JOUR A1 - Baumann, Elisabeth A1 - Pohle, Ulrike A1 - Zhang, Edward A1 - Allen, Thomas A1 - Villringer, Claus A1 - Pulwer, Silvio A1 - Gerhardt, Holger A1 - Laufer, Jan T1 - A backward-mode optical-resolution photoacoustic microscope for 3D imaging using a planar Fabry-Pérot sensor JF - Photoacoustics N2 - 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-Pérot 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. KW - optical-resolution photoacoustic microscopy KW - backward-mode imaging KW - dual-wavelength KW - continuous scanning KW - in vivo imaging KW - optical ultrasound sensing KW - planar Fabry-Pérot interferometer Y1 - 2021 U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:kobv:526-opus4-14701 SN - 2213-5979 VL - 24 SP - 100293 PB - Elsevier ER - TY - CHAP A1 - Lebek, Werner A1 - Heyroth, Frank A1 - Syrowatka, Frank A1 - Villringer, Claus A1 - Goerlitz, Sylvia A1 - Laufer, Jan T1 - Evaluation of fabrication methods for Fabry-Perot polymer film ultrasound sensors T2 - Opto-Acoustic Methods and Applications in Biophotonics VI N2 - Fabry-Pèrot (FP) interferometer sensors enable highly sensitive backward mode acoustic detection in Photoacoustic (PA) imaging. They are transparent to the excitation wavelength, can be placed directly next to the PA source, and offer a broadband frequency response and high acoustic sensitivity. PA tomography using parallelized detection requires high spatial uniformity of the optical and acoustic properties, which can be hampered by contaminations during fabrication that lead to the formation of inhomogeneities and artefacts. The quality and homogeneity of the dielectric and polymer layers have a direct effect on the maximum optical phase sensitivity, and hence acoustic sensitivity. In this study, cross-sectional images of FP sensors were obtained using focused ion beam milling and ultramicrotomy followed by Scanning Electron Microscopy (SEM) and Transmission Electron Microscopy (TEM) to evaluate different fabrication methods. KW - photoacoustic imaging KW - Fabry-Perot sensor KW - parylene-C KW - cocus ion beam KW - electron microscopy Y1 - 2023 U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:kobv:526-opus4-17864 ER - TY - JOUR A1 - Villringer, Claus A1 - Steglich, Patrick A1 - Pulwer, Silvio A1 - Schrader, Sigurd A1 - Laufer, Jan T1 - Electro-optical properties of doped polymers with high transparency in the visible wavelength range JF - Optical Materials Express N2 - The electro-optical (EO) properties of poly(methyl methacrylate) and the photopolymer poly(vinyl cinnamate) doped with varying concentrations of the EO chromophore 2-Methyl-4-nitroaniline were measured. The EO polymers were embedded in Fabry-Pérot etalons for the simultaneous determination of the Pockels and Kerr coefficients from measurements of the fringe shift induced by an external electric field. It was found that the host polymer has a significant impact on the EO performance and that the undoped host polymers exhibit a significant Pockels effect. Moreover, the Kerr effect provides a substantial contribution of 27% to the total change of the refractive index at relatively high electric field strengths of E = 91.2 MV m−1. KW - Bragg reflector KW - fiber optic coupler KW - refractive index KW - spatial light modulator KW - transparency KW - tunable filter Y1 - 2021 U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:kobv:526-opus4-15480 VL - 11 IS - 11 SP - 3801 EP - 3811 PB - Optica Publishing Group ER - TY - JOUR A1 - Kirchner, Thomas A1 - Villringer, Claus A1 - Laufer, Jan T1 - Evaluation of ultrasound sensors for transcranial photoacoustic sensing and imaging JF - Photoacoustics N2 - Photoacoustic imaging through skull bone causes strong attenuation and distortion of the acoustic wavefront, which diminishes image contrast and resolution. As a result, transcranial photoacoustic measurements in humans have been challenging to demonstrate. In this study, we investigated the acoustic transmission through the human skull to design an ultrasound sensor suitable for transcranial PA imaging and sensing. We measured the frequency dependent losses of human cranial bones ex vivo, compared the performance of a range of piezoelectric and optical ultrasound sensors, and imaged skull phantoms using a PA tomograph based on a planar Fabry–Perot sensor. All transcranial photoacoustic measurements show the typical effects of frequency and thickness dependent attenuation and aberration associated with acoustic propagation through bone. The performance of plano-concave optical resonator ultrasound sensors was found to be highly suitable for transcranial photoacoustic measurements. KW - transcranial KW - ultrasound sensor KW - photoacoustic KW - optoacoustic KW - Fabry-Perot Y1 - 2023 U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:kobv:526-opus4-17993 SN - 2213-5979 VL - 33 PB - Elsevier ER -