In JoVE (1)

Other Publications (6)

Articles by Jürgen W. Czarske in JoVE

Other articles by Jürgen W. Czarske on PubMed

Displacement, Distance, and Shape Measurements of Fast-rotating Rough Objects by Two Mutually Tilted Interference Fringe Systems

Journal of the Optical Society of America. A, Optics, Image Science, and Vision. May, 2013  |  Pubmed ID: 23695313

The precise distance measurement of fast-moving rough surfaces is important in several applications such as lathe monitoring. A nonincremental interferometer based on two mutually tilted interference fringe systems has been realized for this task. The distance is coded in the phase difference between the generated interference signals corresponding to the fringe systems. Large tilting angles between the interference fringe systems are necessary for a high sensitivity. However, due to the speckle effect at rough surfaces, different envelopes and phase jumps of the interference signals occur. At large tilting angles, these signals become dissimilar, resulting in a small correlation coefficient and a high measurement uncertainty. Based on a matching of illumination and receiving optics, the correlation coefficient and the phase difference estimation have been improved significantly. For axial displacement measurements of recurring rough surfaces, laterally moving with velocities of 5 m/s, an uncertainty of 110 nm has been attained. For nonrecurring surfaces, a distance measurement uncertainty of 830 nm has been achieved. Incorporating the additionally measured lateral velocity and the rotational speed, the two-dimensional shape of rotating objects results. Since the measurement uncertainty of the displacement, distance, and shape is nearly independent of the lateral surface velocity, this technique is predestined for fast-rotating objects, such as crankshafts, camshafts, vacuum pump shafts, or turning parts of lathes.

Axial Scanning in Confocal Microscopy Employing Adaptive Lenses (CAL)

Optics Express. Mar, 2014  |  Pubmed ID: 24663938

In this paper we analyze the capability of adaptive lenses to replace mechanical axial scanning in confocal microscopy. The adaptive approach promises to achieve high scan rates in a rather simple implementation. This may open up new applications in biomedical imaging or surface analysis in micro- and nanoelectronics, where currently the axial scan rates and the flexibility at the scan process are the limiting factors. The results show that fast and adaptive axial scanning is possible using electrically tunable lenses but the performance degrades during the scan. This is due to defocus and spherical aberrations introduced to the system by tuning of the adaptive lens. These detune the observation plane away from the best focus which strongly deteriorates the axial resolution by a factor of ~2.4. Introducing balancing aberrations allows addressing these influences. The presented approach is based on the employment of a second adaptive lens, located in the detection path. It enables shifting the observation plane back to the best focus position and thus creating axial scans with homogeneous axial resolution. We present simulated and experimental proof-of-principle results.

Volumetric HiLo Microscopy Employing an Electrically Tunable Lens

Optics Express. Jun, 2016  |  Pubmed ID: 27410654

Electrically tunable lenses exhibit strong potential for fast motion-free axial scanning in a variety of microscopes. However, they also lead to a degradation of the achievable resolution because of aberrations and misalignment between illumination and detection optics that are induced by the scan itself. Additionally, the typically nonlinear relation between actuation voltage and axial displacement leads to over- or under-sampled frame acquisition in most microscopic techniques because of their static depth-of-field. To overcome these limitations, we present an Adaptive-Lens-High-and-Low-frequency (AL-HiLo) microscope that enables volumetric measurements employing an electrically tunable lens. By using speckle-patterned illumination, we ensure stability against aberrations of the electrically tunable lens. Its depth-of-field can be adjusted a-posteriori and hence enables to create flexible scans, which compensates for irregular axial measurement positions. The adaptive HiLo microscope provides an axial scanning range of 1 mm with an axial resolution of about 4 μm and sub-micron lateral resolution over the full scanning range. Proof of concept measurements at home-built specimens as well as zebrafish embryos with reporter gene-driven fluorescence in the thyroid gland are shown.

Transmission of Independent Signals Through a Multimode Fiber Using Digital Optical Phase Conjugation

Optics Express. Jun, 2016  |  Pubmed ID: 27410664

Multimode fibers are attractive for a variety of applications such as communication engineering and biophotonics. However, a major hurdle for the optical transmission through multimode fibers is the inherent mode mixing. Although an image transmission was successfully accomplished using wavefront shaping, the image information was not transmitted individually for each of the independent pixels. We demonstrate a transmission of independent signals using individually shaped wavefronts employing a single segmented spatial light modulator for optical phase conjugation regarding each light signal. Our findings pave the way towards transferring independent signals through strongly scattering media.

Wavefront Shaping for Imaging-based Flow Velocity Measurements Through Distortions Using a Fresnel Guide Star

Optics Express. Sep, 2016  |  Pubmed ID: 27661942

Imaging-based flow measurement techniques, like particle image velocimetry (PIV), are vulnerable to time-varying distortions like refractive index inhomogeneities or fluctuating phase boundaries. Such distortions strongly increase the velocity error, as the position assignment of the tracer particles and the decrease of image contrast exhibit significant uncertainties. We demonstrate that wavefront shaping based on spatially distributed guide stars has the potential to significantly reduce the measurement uncertainty. Proof of concept experiments show an improvement by more than one order of magnitude. Possible applications for the wavefront shaping PIV range from measurements in jets and film flows to biomedical applications.

Spiral Phase Mask Shadow-imaging for 3D-measurement of Flow Fields

Optics Express. Nov, 2016  |  Pubmed ID: 27906309

Particle tracking velocimetry (PTV) is a valuable tool for microfluidic analysis. Especially mixing processes and the environmental interaction of fluids on a microscopic scale are of particular importance for pharmaceutical and biomedical applications. However, currently applied techniques suffer from the lag of instantaneous depth information. Here we present a scan-free, shadow-imaging PTV-technique for 3D trajectory and velocity measurement of flow fields in micro-channels with 2 µm spatial resolution. By using an incoherent light source, one camera and a spatial light modulator (LCoS-SLM) that generates double-images of the seeding particle shadows, it is a simply applicable and highly scalable technique.

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