Monitoring pitting corrosion in real-time and non-destructively is a critical challenge in material science. This study introduces dynamic speckle analysis as an innovative approach to quantitatively track pitting corrosion in metallic structures. Pitting corrosion, a major cause of structural failure due to hole formation, is effectively visualized using this technique. Dynamic speckle patterns, generated by laser light scattering off the corroded surface, reveal both the activity and progression of corrosion. We employ a range of graphical and numerical statistical parameters for detailed analysis. Notable for its low cost, ease of implementation, and quasi-in-situ capabilities, our method offers a significant advancement in the study of corrosion. It holds great promise for broader applications in both natural and industrial settings, presenting a versatile tool for material degradation assessment.
This paper presents the use of oblique illumination in self-referencing digital holographic microscopy (SR-DHM) to separate the interfering beams and enhance the resolution. SR-DHM is a compact and vibration-immune quantitative phase microscopy technique in which the interference of the object beam with part of itself forms the digital hologram. However, one drawback with SR-DHM is that both interfering beams contain object information that may overlap and hinder proper reconstruction. This study shows that using oblique illumination in off-axis DHM configurations separates the two interfering beams' spectra in the Fourier space, which can be used in SR-DHM to separate the overlapping beams' information without any restriction on the sample or the Field of View (FoV). The technique's capability is first shown in lateral shearing SR-DHM using a glass plate in which the object beams reflected from the front and back surfaces of a thick glass plate interfere and form the hologram. Using oblique illumination in this setup removes the redundant information from the FoV and improves the resolution twice. On the other hand, the technique is applied in SR-DHM using Lloyd's mirror, in which part of the object beam reflected from the Lloyd's mirror interferes with the part that arrives straightly at the camera plane. By tuning the fringe density in this setup using the illumination angle, we show that the interfering beams can be separated and the two simultaneous holograms can be recorded and reconstructed without overlapping information. This feature can be used for single-shot 1D resolution enhancement without overlapping information. The samples used in our validation experiments are a USAF test target and a 1D phase grating.
Quantitative three-dimensional (3-D) imaging of living cells provides important information about the cell morphology and its time variation. Off-axis, digital holographic interference microscopy is an ideal tool for 3-D imaging, parameter extraction, and classification of living cells. Two-beam digital holographic microscopes, which are usually employed, provide high-quality 3-D images of micro-objects, albeit with lower temporal stability. Common-path digital holographic geometries, in which the reference beam is derived from the object beam, provide higher temporal stability along with high-quality 3-D images. Self-referencing geometry is the simplest of the common-path techniques, in which a portion of the object beam itself acts as the reference, leading to compact setups using fewer optical elements. However, it has reduced field of view, and the reference may contain object information. Here, we describe the development of a common-path digital holographic microscope, employing a shearing plate and converting one of the beams into a separate reference by employing a pin-hole. The setup is as compact as self-referencing geometry, while providing field of view as wide as that of a two-beam microscope. The microscope is tested by imaging and quantifying the morphology and dynamics of human erythrocytes.
KEYWORDS: Digital holography, Holograms, Holography, Microscopy, 3D image reconstruction, Optical signal processing, 3D image processing, Microscopes, Beam splitters, Visualization
Lateral in-homogeneities in lipid compositions cause microdomains formation and change in the physical properties of biological membranes. With the presence of cholesterol and mixed species of lipids, phospholipid membranes segregate into lateral domains of liquid-ordered and liquid-disordered phases. Coupling of two-dimensional intralayer phase separations and interlayer liquid-crystalline ordering in multicomponent membranes has been previously demonstrated. By the use of digital holographic microscopy (DHMicroscopy), we quantitatively analyzed the volumetric dynamical behavior of such membranes. The specimens are lipid mixtures composed of sphingomyelin, cholesterol, and unsaturated phospholipid, 1,2-dioleoyl-sn-glycero-3-phosphocholine. DHMicroscopy in a transmission mode is an effective tool for quantitative visualization of phase objects. By deriving the associated phase changes, three-dimensional information on the morphology variation of lipid stacks at arbitrary time scales is obtained. Moreover, the thickness distribution of the object at demanded axial planes can be obtained by numerical focusing. Our results show that the volume evolution of lipid domains follows approximately the same universal growth law of previously reported area evolution. However, the thickness of the domains does not alter significantly by time; therefore, the volume evolution is mostly attributed to the changes in area dynamics. These results might be useful in the field of membrane-based functional materials.
In this paper, the Transport of Intensity Equation (TIE) for testing of an aspheric surface is verified experimentally. Using simulation, a proper defocus distance Δ𝑧 that leads to an accurate solution of TIE is estimated whenever the conic constant and configuration of the experiment are known. To verify this procedure a non-nulled experiment for testing an aspheric is used. For verification of the solution, the results are compared with the Shack-Hartmann sensor. The theoretical method and experimental results are compared to validate the results.
In this paper we use digital projection moiré (DPM) method to analyze the non-linear behavior of sandwich beams with compliant foam core. These cores are highly flexible with respect to the face sheets and their behavior is associated with localized effects in the form of localized displacements and stresses, which in turn influence the overall behavior of sandwich beams. In this study we compare the results of three point bending with Finite Element Analysis (FEA) results that are obtained from the ABAQUS finite element code. We have shown that DPM experimental results are in good agreement with FEA simulations. It is suggested that the presented method can be used as a simple, advantageous and user friendly whole-field testing technique for many applications in evaluation of composite materials and sandwich structures.
Phase distribution may be determined by measuring only the intensity distributions along the optical axis via the Transport of Intensity Equation (TIE). TIE has been a viable alternative to interferometry techniques for experimental conditions where those techniques perform poorly. These conditions are either because of the requirement one applies on the spatial and temporal coherence of the optical source or because of sensitivity and resolution issues. Optical testing is crucial in applications using manufactured optical elements. In this paper, we developed a method and experimental realizations capable to use both Shake-Hartman wavefront sensing (SHWS) and TIE method for testing transparent and reflective optical surfaces. The integration of TIE and SHWS has the advantage for obtaining high spatial resolution and wide dynamic range which cannot be obtained using only one of those methods. We showed that the retrieved phase profile and quantified surface variations of unknown samples from both methods are in very good agreement with each other.
Digital holographic microscopy (DHM) is an effective and non-destructive technique for quantitative phase contrast imaging of biological samples and living organelles. In this paper, using a simple and stable common-path DHM setup we study lipid bilayer dynamics and detect their morphological changes. Stacks of lipid amphiphilic molecules in excess water and at the presence of an external stimulus, stress, or force have great capability for the formation of multilamellar cylindrical tubes that are called myelin figures(MFs). MFs can be found in various healthy and diseased living cells and their formation and dynamics in various conditions involve mysterious configurations that have been of high interest. We utilized nanoparticles solved in water with different concentrations as an external stimulus for MFs of POPC lipid. The nanoparticles are injected into the sample container via a microinjection pump in a constant rate and MFs growth rate and their volume changes are measured by a compact digital holographic system. The setup is based on a binocular conventional microscope making the setup very stable against vibrations and noises. The recorded holograms are then computationally reconstructed. The measurements and investigations are performed by analyzing the reconstruction process. We showed that nanoparticles increase the growth rate of MFs during the first few seconds. However, after few seconds, the growth rate does not alter significantly comparing to the absence of nanoparticles.
Digital holographic microscopy (DHM) provides a non-destructive measurement technique based on calculation of optical path length changes of the sample under study. If the changes are caused by refractive index variations within a constant physical thickness, the technique results in the precise measurement of the refractive index . In this paper, DHM is utilized to map the refractive index over a wide surface of a T-shaped micro channel. The micro channel is filled up by a solution of two chemical reactant fluids. In some chemical reactions the refractive index of the resultant may be highly different from the refractive indices of the reactants. Using microinjection pumps methane and water as reactants are injected into the channel at the same flow rates. Changes in optical path ways are measured by live recording the digital holograms during the fluids interaction for all the field of view pixels. The holograms are recorded by a detector and post processed by a computer in order to reconstruct the phase profile changes though angular spectrum propagation method. The changes in the refractive indices that take place during the reaction process, are viewed by the detector and are calculated and mapped for the T channel and Y channel.
In this paper using an optical method based on diffraction phenomenon, we studied surface tension of fluids. Diffraction patterns of a laser beam diffracted from surface waves, induced by an external acoustic wave generator, provides information of the surface of fluids. This information, in turn, enables calculating an experimental dispersion relation and surface tension of fluids. Spherical and cylindrical surface waves on fluids are generated by sticking a long thin needle and a thin metal plate, respectively, to a loudspeaker. Turning on the generator, the needle (or metal plate) causes waves on the surface, which act as a diffraction grating to the incident laser beam. The experiment and analysis were performed for both Newtonian and non-Newtonian fluids. Distilled water was used as a Newtonian sample fluid, and polyacrylamide solution was used as a non-Newtonian one. Our results predict considerable differences between Newtonian and non-Newtonian fluids behavior in terms of their surface wave dispersion.
In this work, we utilize digital holographic microscopy technique and also conventional video
microscopy to detect the dynamic morphological changes of bacteria membrane in presence of silver ions. Silver ions
have shown strong inhibitory effects on bacteria and can be used as antibacterial. We used E. coli as a sample and the
influences of the ions were compared in terms of the variations in volume of E. coli for different concentration of silver
ions in the buffer and various incubation times. In a controlled experiment using a microinjecting pump the concentration
of antibacterial is increased, the movement of a single or a set of bacteria are monitored live, and successive digital
holograms are recorded. The recorded holograms by digital camera can be post-processed to three dimensional
reconstruction of the samples and measurement of quantitative structural changes in various interacting time of the
bacteria.
Digital holographic microscopy (DHM) provides a non-destructive and quantitative phase contrast imaging that
is suitable for high resolving investigations of living cells. On the other hand, for many applications including cell
analysis the immobilization of the sample under study is a crucial task. Optical trap is an elegant candidate to
immobilize the micro samples. In this work, DHM is integrated with an optical trapping setup. This combination
is of particular advantage for quantitative visualization of three dimensional structures that are trapped by laser
beam. The recorded hologram by CCD can be post-processed to three dimensional (3D) reconstruction of the
trapped objects.
We discuss a new technique to generate force gradient in arrays of optical traps. The arrays can be configured in two or three dimensions by means of phase diffractive optical elements displayed on a spatial light modulator. The design of the diffractive optical elements is based on the approach of spherical wave propagation and superposition, which enables to individually control the strength of each optical trap. Computer simulation and experimental results are discussed for two and three dimensional arrays of traps. An example with silica micro-beads trapped with different forces in two different planes is presented to demonstrate the validity of our approach.
KEYWORDS: Diffraction, Fourier transforms, Near field, Fractional fourier transform, Direct methods, Free space, Wave propagation, Free space optics, Near field optics, Near field diffraction
In this paper we compare different free space propagation algorithms based on fast Fourier transform (FFT). They are
used to calculate 1D and 2D difiaction patterns in near field and far field as well. Four algorithms are considered:
angular spectrum propagation, direct integral formulation, fractional Fourier transform using single FFT (S_FFT) and
fractional Fourier transform using two FFT (D_FFT). We compare these algorithms and discuss their advantages and
drawbacks for one and two-dimensional objects.
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