In the case of in-line digital holographic microscopes the retrieval of the phase information is indispensable to remove the twin image noise and to characterize the thickness and refractive index distribution of the measured objects. The existing phase reconstructing algorithms, especially, when the goal is to reach high resolution, suffer from really slow convergence. This can prevent their practical applicability. We introduce here a simple method that ensures accurate, high resolution and fast phase retrieval from two holograms recorded in different distances. The so far frequently applied phase retrieval algorithms converge with tolerable speed if the Fresnel number of the system is small enough. This is the consequence that in this case the diffraction of the twin image spreads substantially over the applied object support and thus the support constraint can provide sufficient amount of data for the efficient phase retrieval. However, if the recording measurement Fresnel number is small, the finite aperture of the hologram limits the proper recording of the high spatial frequencies of the object diffraction. In this case the convergence of the phase retrieval will be really fast, but inaccurate. Therefore, we propose to record two different holograms with small and large Fresnel numbers accordingly. From the first one we can reconstruct the low spatial frequencies of the object at a high rate. Subsequently, we can use this partial reconstruction to speed up the reconstruction of the so far not correctly recalled high spatial frequencies, by applying the second hologram.
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.
Our digital holographic (DH) approach can be used to study tissue structures both in vitro and in vivo. This
DHM architecture can produce three color microscopic 3D and 4D (video) images. We record 3 color (RGB)
holograms with single exposures, and the perfect compensation of color crosstalk is solved. An in-line holographic
setup and reconstruction algorithms are presented with demonstrative simulations and experimentally captured
and numerically reconstructed images. Comparing the individually reconstructed color images with each other
can provide information both for recognition of different types of cells or microorganisms, and for diagnostic
purposes as well. Experimental example is given observing microscopic hydro-biological organisms using a color
digital holographic microscope.
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.
A portable programmable opto-electronic analogic CNN computer (Laptop-POAC) has been built and used to recognize and track targets. Its kernel processor is a novel type of high performance optical correlator based on the use of bacteriorhodopsin (BR) as a dynamic holographic material. This optical CNN implementation combines the optical computer's high speed, high parallelism (≈106 channel) and large applicable template sizes with flexible programmability of the CNN devices. Unique feature of this optical array computer is that programming templates can be applied either by a 2D acousto-optical deflector (up to 64x64 pixel size templates) incoherently or by an LCD-SLM (up to 128x128 size templates) coherently. So it can work both in totally coherent and partially incoherent way, utilizing the actual advantages of the used mode of operation. Input images are fed-in by a second LCD-SLM of 600x800 pixel resolution. Evaluation of trade-off between speed and resolution is given. Novel and effective target recognition and multiple-target-tracking algorithms have been developed for the POAC. Tracking experiments are demonstrated. Collision avoidance experiments are being conducted. In the present model a CCD camera is recording the correlograms, however, later a CNN-UM chip and a high-speed CMOS camera will be applied for post-processing.