Szabolcs Tőkés

In-line color digital holographic microscope for water quality measurements

We introduce a color digital holographic microscope for measuring the biological content of water samples. Our approach uses single shot RGB exposure in an in-line holographic setup to obtain color images. With the application of appropriate numerical algorithms we can fulfill color crosstalk compensation, segmentation, and twin image removal tasks, and we obtain good quality color image reconstructions with 1μm resolution from a 1mm3 volume. We briefly compare the conventional color CCD/CMOS and the Foveon X3 sensor for color digital holographic applications. The in-line holographic setup and reconstruction algorithms are presented with demonstrative simulations, experimentally captured and numerically reconstructed images.

Special multicolor illumination and numerical tilt correction in volumetric digital holographic microscopy

We introduce a color imaging method in our digital holographic microscope system (DHM). This DHM can create color images of freely floating, or moving objects inside a large volume by simultaneously capturing three holograms using three different illumination wavelengths. In this DHM a new light source assembly is applied, where we use single mode fibers according to the corresponding wavelengths that are tightly and randomly arranged into a small array in a single FC/PC connector. This design has significant advantages over the earlier approaches, where all the used illuminations are coupled in the same fiber. It avoids the coupling losses and provides a cost effective, compact solution for multicolor coherent illumination. We explain how to determine and correct the different fiber end positions caused tilt aberration during the hologram reconstruction process. To demonstrate the performance of the device, color hologram reconstructions are presented that can achieve at least 1 µm lateral resolution.

In-line hologram segmentation for volumetric samples

We propose a fast, noniterative method to segment an in-line hologram of a volumetric sample into in-line subholograms according to its constituent objects. In contrast to the phase retrieval or twin image elimination algorithms, we do not aim or require to reconstruct the complex wave field of all the objects, which would be a more complex task, but only provide a good estimate about the contribution of the particular objects to the original hologram quickly. The introduced hologram segmentation algorithm exploits the special inner structure of the in-line holograms and applies only the estimated supports and reconstruction distances of the corresponding objects as parameters. The performance of the proposed method is demonstrated and analyzed experimentally both on synthetic and measured holograms. We discussed how the proposed algorithm can be efficiently applied for object reconstruction and phase retrieval tasks.

Combined optically addressable spatial light modulator for affordable adaptive optics

Combining high-end sensor, display and field programmable gate array technologies a new combined optically addressable spatial light modulator device is developed, and built. Parallel, programmable hardware provides an efficient way to process the measured wavefront data. Using these data and appropriate phase modulation of the built in LCOS display a complete adaptive optic system can be implemented. As it is built from commercially available, sophisticated components it provides an affordable solution, without real compromise between the achievable resolution, speed and overall performance. Primarily, we intend to apply this device in solar telescopes, where high speed, high resolution, correlation based wavefront sensing is required.