The paper is concerned with the experimental study of the time evolution of a single laminar vortex ring generated at the interface between water and dimethyl carbinol. The experiments were performed by the submerged injection with a constant rate of dimethyl carbinol (isopropyl alcohol) in a water tank. The dynamics of the vortex formation was recorded at 1000 fps with a Photron Fastcam SA1 camera, equipped with a microscopic Edmund Optics objective. A symmetrical buoyant vortex ring with an elongated topology was observed at the interface between the two immiscible liquids. The analyses of the time dependence of the vortex rings disclosed three regions for the evolution of the interface: one dominated by inertia force, a transition region and a third region, dominated by buoyancy force.
This study is presenting the theoretical approach and the practical results of a precise activity involved in the hologram reconstruction in order to find the optimally focused image of MG63 osteoblast-like cells cultivated on polymeric flat substrates. The morphology and dynamic of the cell is investigated by digital holographic microscopy (DHM) technique. The reconstruction is digitally performed using an algorithm based on the scalar theory of diffraction in the Fresnel approximation. The quality of the 3D images of the cells is crucially depending on the focusing capability of the reconstruction chain to fit the parameters of the optical recorder, particularly the focusing value. Our proposal to find the focused image is based on the images decomposition on gray levels and their histogram analysis. More precisely the focusing criterion is based on the evaluation of the form of this distribution.
The diffraction patterns (DPs) from helical phase distributions were intensively studied due to their peculiar capability of carrying orbital angular momentum. In the present study, we investigated the combination between a helical phase distribution and another distribution: axicon in our case. Such phase distributions were digitally embedded into holographic masks (HMs). The reconstruction step is performed by simulating the propagation through these HMs, using scalar diffraction theory, Fraunhofer approximation. The spatial intensity arrangement of the DPs is investigated linked with the radial and azimuthal constructive parameters values of the diffractive phase structures embedded in the HMs and transferred in these DPs. Keywords: helical phase distribution
In this paper we present several numerical simulations of the surface plasmon resonance for Kretschmann type configuration in a metal-chalcogenide waveguide. We assume that the chalcogenide (GaLaS) waveguide layer have finite thickness, whereas the gold film layer and the air cover layer are semi-infinite layers (from an optical point of view). We determined the thickness of the chalcogenide film for which plasmonic resonant coupling of the incident radiation to the waveguide occurs. We calculated the propagation constant for the TE- and TM- modes (both for visible and IR domain), the attenuation coefficient and the electromagnetic field distribution within the waveguide. The obtained results provide the conditions for design an optical memory device 2D based on light-light interaction in plasmonic configuration.
We generated holographic masks starting with the interference between the reference beam and the signal beam, which is diffracted by the object. We investigate additive and multiplicative combinations between conical and helical phase distributions as compound objects to be inserted in the signal beam. We explored experimentally the dynamics of the diffracted intensity patterns, in two and three dimensions, after these holographic masks are addressed onto a programmable spatial light modulator. The diffracted intensity spatial arrangement contain information about constructive parameters used for holographic masks generation and exhibit asymmetric shapes and peaks along the optical axis in all analyzed compound objects. We introduce a reading mask in the optical path and, by analyzing changes of the spatial distribution in the final diffracted intensity arrangement, is possible to read the values of the constructive parameters. The generation of these reading masks in each case is discussed.
The study of cells-substrate interaction became a stringent subject in the past decades, since an increasing
variety of new materials and methods have been involved in tissue engineering or implants techniques. The investigation
of this interaction using optical methods is a challenge, especially since these substrates are not optically polished. Due
to their roughness in the micrometric or submicrometric range, the polymeric substrates offers good conditions for cells
adhesion, but the characterization of cells properties can be hindered. In this study, we use Polypyrrole thin films, acting
as substrates for cultured osteoblast-like MG63 cells having applications in tissue engineering for in vivo-like scaffolds.
As characterization technique, we chose digital holographic microscopy, a single-shot technique, to obtain quantitative
information about the sample features in a plane perpendicular to the substrate. Different parameters were tested in the
experimental setup with the aim of finding the optimal conditions for details visualization. The reconstructed 3D images
were filtered using a combination of analytical and implicit functions from MATLAB to exclude small/large objects,
which correspond to Polypyrrole droplets to clearly identify the cells contour for quantitative measurements regarding
their dimensions. These data were correlated with the effects on osteoblasts viability and differentiation. Also, the
thickness and the refractive index of the substrate were determined using the decoupling procedure.
In this paper we report some experimental results concerning the absorption/transmission measurements in the
canine oocytes. For this we used an argon ion laser radiation (having 514 nm, 502 nm, 496 nm, 488 nm, 477 nm, 472
nm, 465 nm, 457 nm wavelength). These absorption/transmission measurements have been performed using a UV/VIS
high resolution spectrometer from Ocean Optics as detector. The objective of this paper is to evaluate some
characteristics: refractive index, maturity and quality which characterize the canine oocytes. In our work, we have used
a noninvasive optical method for evaluation quality of canine oocytes.
Optoelectronic techniques can be applied for the study of transparent objects, followed by the processing of the recorded images on a video camera, after the laser beam passes through the investigated object. In this paper we present our study on a polycarbonate plate with optical polished surfaces, subjected on mechanical stresses perpendicular to the laser beam propagation axis. The results of this study include the values for material constants. Three experimental arrangements were employed: a plane polariscope, a circular polariscope and an interferometric setup. The recorded images in coherent light contain fringes variation with increased mechanical stress. They are processed using our MATLAB codes to determine the state of the stress at various points in the investigated sample. The measurements in a polariscopic assembly demonstrate the photoelastic properties of this composite material. In the plane polariscope arrangement, we can visualize the main stress directions and also the points with equal maximum shear stress magnitude; in circular polariscope we can visualize only the points with equal maximum shear stress magnitude; and in the interferometric setup are highlighted the refractive index variations which are linked with the phase changes and the applied stress. We apply the shift theorem from the Fourier theory, on the experimental images from the interferometric setup and on simulated ones.
Computer generation of holograms is a technique used to obtain a specific laser intensity distribution in far field starting from a desired image. In the process of hologram computing, the phase information must be considered. In this study we will present our code which ensures a fast link between the CCD camera (which records real macroscopic scenes), computer (where holograms are generated) and the spatial light modulator (where the holograms are displayed) to obtain on a screen a holographic displayed movie in real time. The aim of this work was to build interactive holographic systems. The challenge was not only to develop such a code, which can work for a suite of images taken by the CCD, but also to process them in a way that the delay of resulting reconstruction is unperceivable for human eye. For the veracity of the method we will present both simulation and experimental results.
Digital holographic microscopy is a technique which enables real time monitoring of fast phenomena by using high
speed sensors of video cameras. Using this advantage, we obtain holographic images of flow in microcavities,
employing a CMOS video camera sensor with acquisition rate of 10 000fps. The corresponding reconstructed 3D image
for different flow conditions is obtained from a single hologram using simulations based on the Fresnel approximation.
We develop an automated image processing procedure in order to obtain quantitative information about the dynamic
contact angle evolution, the shape and velocity of an approximately 300μm wide portion from the water-air meniscus
interface in different microscopic cavity geometries.
The aim of this research is to calculate the refractive index of transparent atmospheric aerosols, which have biological
origin, using a digital holographic microscopy technique (DHM). The samples are collected on filters, using miniature
impactors for particles with dimensions smaller than 10μm (on even one axis), from a height of over 20 meters, in
Magurele, a rural location near the urban and industrial agglomeration of the capital city, Bucharest. Due to their organic
or inorganic origin, each atmospheric aerosol particle has different size, shape and optical properties which have a
determinant role in LIDAR measurements. We record on a CCD camera hundreds of holograms which contain the
diffraction pattern from every aerosol particle superposed with the reference wave. Digitally, we scan the entire volume
of one particle with nanometric resolution (using an algorithm based on the Fresnel approximation). The calibration was
done using an object with known dimensions fabricated by e-beam lithography and some complementary measurements
were done in confocal microscopy. Our analysis separates four main classes of atmospheric aerosols particles (wires,
columns, spherical fragments, and irregular). The predominant class in the investigated period is the first one, which has
biological origin and the refractive index was calculated starting from the phase shift introduced by them in the optical
path and models for their cylindrical shape. The influence of spatial filtering in the reconstructed object images was
A numerical analysis of TE mode of electric field propagation through the interface between a thin film of TiO2 and
periodic metal slits of silver is presented. The lossy metallic slits are optically described by Drude model. A grid of
regular slits generates sharp hotspots of electric field at the exit plane. Adding a 2D rectangular photonic crystal made of
air cylinders in titanium dioxide will enhance the electric field at the exit from the metallic slits without any loses in
propagation distance and peak width. An optimization of geometrical parameters of metallic slits and photonic crystals is
made for the propagation of a visible incident radiation with the wavelength of 650nm.
Computer generated holograms are designed starting with the images of the desired objects, which will be formed on a
screen, after laser diffraction on the holograms. In the design step, these digitized images are placed inside the signal
window. We analyzed the influence of the size and the position of the signal window on the parameters values of the
diffracted intensity distribution (diffraction efficiency and uniformity). First, we considered simple objects (three points
and a line with a given size) and then an object of a logo type. The distance between the hologram plane and the image
plane was also preset. Simulation and experimental results are presented.
We investigated the recording-erase processes of a hologram in photochromic glass using a continuum Nd:YVO4 laser
radiation (λ=532nm). Its dynamic was evaluated in the reconstruction step. A bidimensional micrograting pattern was
formed and visualized in photochromic glass. In the reconstruction step, we monitored the time decay of the diffraction
efficiencyin plane oh the reconstructed object image. It gave information about the processes induced inside the material.
Recording and reconstruction processes were done in an off-axis setup, and the movies of the reconstructed object
images were recorded on a CCD camera. Measurements from the reconstruction kinetic, gave us information used to
computing the variation of the refractive index of the photochromic glass during these processes.
We analyze an optical system consisting of a number of basically elements (BE) arranged in a quasi-periodic structure (QPS) of phyllotaxis type, which offers the best packing in many natural bodies. In our simulations, we change the parameters which generate this QPS to find its diffractive optical properties. This structure is then made on glass using e-beam lithography. To characterize this QPS, we use the digital holography (DH) method to reconstruct the amplitude and also the phase in object plane (QPS plane). Using different parameters of the spherical reference wave for holograms recording we change the contrast in holograms to improve the reconstruction of the object.
A new architecture with two phases-only diffractive elements and one decryption mask for optical control access system
is presented. Only three different persons which keep this element have the permission to access together. The Iterative
Fourier Transform Algorithm (IFTA) is analyzed for phase-only diffractive optical elements (PODE) design with
different constraints in the input and output plane and the optimal variant is chosen for better image quality in the output
plane (big value for diffraction efficiency and small value for merit function and signal to noise ratio). For higher
security we propose different incident waves. That are compared with the case when the first phase-only diffractive
element and decryption masks are designed together in an extended iteration and the output images of them (first desired
image) is taken over the second phase-only diffractive element. In order to increase security level, this finally PODE are
designed to increase some parts from the first desired image. Only with this condition the key image on the detector is
Here we study the temporal evolution of a magnetemechanical, inverted spherical pendulum. The oscillator is a rigid,
stainless steel, hollow needle. The needle has one end fixed in a spherical-like articulation, while the other extremity
has no mechanical contact. The oscillation is driven by a longitudinal, periodically magnetic field added to a constant
value of a static field. A video camera takes simultaneously the optical images of the projections of the oscillating
needle along two mutually normal directions. The pairs of temporal sequences are analyzed in the real space, phase
space and Fourier space. Among all the external parameter that can be usually varied, like the strength of the static
magnetic field, the amplitude and the frequency of the driving magnetic field, or the momentum of inertia of the
oscillating body, of a crucial importance seems to be the magnetc-mechanical feed-back of the oscillating system.
A pulsed laser has been used to generate a laser plasma plume (a dusty plasma) from a pressed powder target situated in the room atmosphere. This dusty plasma has been analyzed with a probe laser beam, a polarizing interferometer and a CCD camera. Our results show that this dusty plasma is a depolarizing medium. The maximum depolarization degree of the probe laser beam is 5%.
Considering the rise time (understanding the rise speed as well) of the electrical intensity of the pumping pulse as the key parameter characterizing the output power of a copper-type laser, we present here a simplified model of the main kinetic processes occuring during the electrical pumping pulse and afterglow in a Ne-CuBr laser. The a priori knowledge of the typical temporal behavior of the electron density and electron temperature reduces the number of coupled differential equation to be solved. The importance of the parasitic radiative filling of the lower laser levels 2D via channels that are not involving the upper laser levels 2P is enhanced. The comparative green-yellow lasing efficiencies and the temporal timing of the optical pulses with respect to the excitation pulse are consistent with the experiments.
In this paper we present a glycerin-filled interferometer which is suited to determine the thermally induced space-time refractive index profile of an optical, uranyl-ion-doped glass. The refractive index of the sample changes when irradiated with an Ar+ laser or a pulsed Nd-YAG laser and modifies the interference pattern of a probe beam. According to the task performed, the interferometer is used in longitudinal and transversal configurations. Using the model of the thermal absorption and diffusion, one can find the relation between the refractive index variation, temperature gradient and phase shift of the interference pattern. We calculate the refractive index changes of the on and off axis as well as its temporal variation during the relaxation process. The modifications of a thermally induced phase grating is interpreted in terms of a one-dimensional, structured gaussian beam obtained from a double refractive crystal of KDP (KH2PO3).