Edge enhancement of a phase-conjugate image with a mutually pumped phase conjugator

Usually edge enhancement of optical images is produced by introduction of loss into the low spatial frequency components of the image-bearing beam in the Fourier plane of a lens. We report on edge-enhanced phase-conjugate images from a mutually pumped conjugator accomplished by spatial filtering in the Fraunhofer diffraction region of the input beams. High-resolution (128-160 lines/mm) edge-enhanced images are obtained through traditional spatial filtering in the Fourier plane and in the Fraunhofer regime. Amplification of these edge-enhanced images is observed with some loss of high spatial resolution (50 lines/mm).     

Contrast enhancement of electronic speckle pattern interferometry addition fringes

The electronic speckle pattern interferometer in the double-pulse addition mode can be used to measure physical parameters in unstable environmental conditions. Owing to additive optical noise, however, the fringe patterns obtained have poor contrast. Some methods that use subtraction of addition double-pulsed fringe patterns improve fringe visibility but impose a limitation in measurement time ranges. To increase this range, to be limited by only the pulse separation, the contrast enhancement of double-pulsed addition-fringe patterns with a spatial filter based on local-standard-deviation measurements is investigated. Computer simulations and experimental results are presented.     

Phase recovery from a single interferogram with closed fringes by phase unwrapping

We describe a new algorithm for phase determination from a single interferogram with closed fringes based on an unwrapping procedure. Here we use bandpass filtering in the Fourier domain, obtaining two wrapped phases with sign changes corresponding to the orientation of the applied filters. An unwrapping scheme that corrects the sign ambiguities by comparing the local derivatives is then proposed. This can be done, assuming that the phase derivatives do not change abruptly among adjacent areas as occurs with smooth continuous phase maps. The proposed algorithm works fast and is robust against noise, as demonstrated in experimental and simulated data.     

Robust phase demodulation of interferograms with open or closed fringes

We present two robust algorithms for fringe pattern analysis with partial-field and closed fringes. The algorithm for partial-field fringe patterns is presented as a refinement method for precomputed coarse phases. Such an algorithm consists of the minimization of a regularized cost function that incorporates an outlier rejection strategy, which causes the algorithm to become robust. On the basis of the phase refinement method, we propose a propagative scheme for phase retrieval from closed-fringe interferograms. The algorithm performance is demonstrated by demodulating closed-fringe interferograms with complex spatial distribution of stationary points and gradients in the illumination components.     

Dynamic analysis of an embedded microbeam carrying a moving microparticle based on the modified couple stress theory

In this study, analytical and numerical solution procedures are proposed for vibration of an embedded microbeam under action of a moving microparticle based on the modified couple stress theory (MCST) within the framework of Euler–Bernoulli beam theory. The governing equation and the related boundary conditions are derived by using Hamilton’s principle. The closed form solution of the transverse deflections of the embedded microbeam is obtained using the finite Fourier sine transformation. In the numerical solution, the dynamic deflections are computed by using the Lagrange’s equations in conjunction with the direct integration method of Newmark. The static deflections are also obtained analytically. A detailed parametric study is conducted to study the influences of the material length scale parameter, the Poisson’s ratio, the velocity of the microparticle and the elastic medium constant as well as the solution procedures on the dynamic responses of the microbeam. For comparison purpose, static deflections and free vibration frequencies of the microbeam are obtained and compared with previously published studies. Good agreement is observed. The results show that the above mentioned effects play an important role on the dynamic behavior of the microbeam.     

Picoliter rheology of gaseous media using a rotating optically trapped birefringent microparticle

An optically trapped birefringent microparticle is rotated by a circularly polarized beam in a confined gaseous medium. By recording the terminal rotation velocity and the change in polarization of the incident trapping beam, we determine the viscosity by probing a picoliter volume of air, carbon dioxide, and argon in the vicinity of the microparticle. We also characterize the optical force acting on a trapped particle in air using the generalized Lorenz-Mie theory taking into account the aberrations present. This opens up a new potential application of optical tweezers for the accurate measurement of gas viscosity in confined geometries.     

Probing of a random phase screen by a focused spatially modulated laser beam: Deflection of interference fringes

Deflection of interference fringes in a diffraction field was investigated under conditions in which a laser beam with a regular interference structure was finely focused onto a random phase screen. It was established that the contrast of the average-intensity fringes depends analytically on the statistical parameters of the screen. Pis’ma Zh. Tekh. Fiz. 25, 56–61 (January 12, 1999)     

On the velocity of a moving phase boundary in solids

Summary A general relationship between the driving force and the velocity of a moving phase boundary in thermoelastic solids is established on the basis of non-equilibrium jump relations at the discontinuity. The non-equilibrium jump relations are formulated in terms of contact quantities and local equilibrium fields. The contact quantities are introduced following ideas of the thermodynamics of discrete systems. It is shown that under certain simplifications the derived relationship can be reduced to a known kinetic relation.     

Adaptive correction to the speckle correlation fringes by using a twisted-nematic liquid-crystal display

An innovative technique for reducing speckle noise and improving the intensity profile of the speckle correlation fringes is presented. The method is based on reducing the range of the modulation intensity values of the speckle interference pattern. After the fringe pattern is corrected adaptively at each pixel, a simple morphological filtering of the fringes is sufficient to obtain smoothed fringes. The concept is presented both analytically and by simulation by using computer-generated speckle patterns. The experimental verification is performed by using an amplitude-only spatial light modulator (SLM) in a conventional electronic speckle pattern interferometry setup. The optical arrangement for tuning a commercially available LCD array for amplitude-only behavior is described. The method of feedback to the LCD SLM to modulate the intensity of the reference beam in order to reduce the modulation intensity values is explained, and the resulting fringe pattern and increase in the signal-to-noise ratio are discussed.     

Wave-optical evaluation of interference fringes and wavefront phase in a hard-x-ray beam totally reflected by mirror optics

The intensity flatness and wavefront shape in a coherent hard-x-ray beam totally reflected by flat mirrors that have surface bumps modeled by Gaussian functions were investigated by use of a wave-optical simulation code. Simulated results revealed the necessity for peak-to-valley height accuracy of better than 1 nm at a lateral resolution near 0.1 mm to remove high-contrast interference fringes and appreciable wavefront phase errors. Three mirrors that had different surface qualities were tested at the 1 km-long beam line at the SPring-8/Japan Synchrotron Radiation Research Institute. Interference fringes faded when the surface figure was corrected below the subnanometer level to a spatial resolution close to 0.1 mm, as indicated by the simulated results.     

Use of multiple loads to extract continuous isoclinic fringes by phase shifting technique

Using a monochromatic light source for illumination, a new approach is proposed which uses two different loads to get continuous isoclinic fringes. A new set of optical arrangements in a plane polariscope setup is proposed for this purpose. The intensity equations are obtained by Jones calculus. The methodology is verified for the problem of a disc under diametral compression.     

Control of phase of fringes in speckle interferometry for application of fringe scanning method

The speckle interferometry is an effective technique in the displacement measurement of a structure with a rough surface. However, when the fringe scanning technique is introduced to speckle interferometry for improving the measurement resolution, generally two speckle patterns before and after the deformation of the measurement object and another speckle pattern obtained under different conditions from these two speckle patterns are required at least. So, three speckle patterns are generally required for precise fringe analysis as a minimum condition. In this paper, a method for introducing the fringe scanning method is proposed by controlling the phase of the specklegram as a fringe image using filtering techniques. Then, the temporal fringe analysis method that uses only two speckle patterns are proposed for speckle interferometry. As the result of experiments, it is shown that high precise fringe analysis can be realized by the fringe scanning methods using only two speckle patterns for the displacement measurement with a large deformation.     

Vibration analyses of a portal frame under the action of a moving distributed mass using moving mass element

Four kinds of moving mass elements, 1st‐node, 2nd‐node, full and short‐range mass elements, are presented, where the 1st‐node (or 2nd‐node) mass element refers to that with mass distributed from the first node (or second node) to the arbitrary position of a two‐node beam element, the full mass element is the special case of the 1st‐node (or 2nd‐node) mass element with mass distributed over the full length of the beam element, while the short‐range mass element is the case with its location arbitrary on a beam element. If the total range of a distributed mass is denoted by R and the length of each beam element is denoted by ??, then, for the case of R???, one may model the distributed mass on the beam using the combination of the 1st‐node, 2nd‐node and full mass elements, while for the case of R<??, one may model the distributed mass using the short‐range mass element. It has been found that the effects of the vertical (?) and horizontal (x?) inertia forces, Coriolis force and centrifugal force induced by the moving distributed mass can be easily taken into the formulations by means of the last concept. To illustrate the application of the presented theory, the dynamic analysis of a pinned–pinned beam and that of a portal frame under the action of a moving uniformly distributed mass are performed by means of the finite element method and the Newmark integration method. Numerical results show that some pertinent factors, such as Coriolis force, centrifugal force, acceleration, velocity and total range of the moving distributed mass, have significant influences on the vertical (?) and horizontal (x?) response of a structure. Copyright © 2005 John Wiley & Sons, Ltd.     

Molecular detection of bacterial pathogens using microparticle enhanced double-stranded DNA probes

Rapid, specific, and sensitive detection of bacterial pathogens is essential toward clinical management of infectious diseases. Traditional approaches for pathogen detection, however, often require time-intensive bacterial culture and amplification procedures. Herein, a microparticle enhanced double-stranded DNA probe is demonstrated for rapid species-specific detection of bacterial 16S rRNA. In this molecular assay, the binding of the target sequence to the fluorophore conjugated probe thermodynamically displaces the quencher probe and allows the fluorophore to fluoresce. By incorporation of streptavidin-coated microparticles to localize the biotinylated probes, the sensitivity of the assay can be improved by 3 orders of magnitude. The limit of detection of the assay is as few as eight bacteria without target amplification and is highly specific against other common pathogens. Its applicability toward clinical diagnostics is demonstrated by directly identifying bacterial pathogens in urine samples from patients with urinary tract infections.     

Examination of singular scalar light fields using wavelet processing of fork fringes

A single frame fork fringe pattern automatic processing method for detecting optical vortices in coherent light fields using two-dimensional continuous wavelet transformation is proposed. When a vortex sign is of no importance, it is sufficient to calculate the fork interferogram modulation distribution and its normalized gradient map to establish vortex locations without resorting to complicated phase calculations. Normalization of modulation gradient maps enables unambiguous vortex discrimination from local modulation minima without phase singularity. The issue of vortex detection resolution versus carrier fringe frequency and orientation is discussed. Corroboration of simulation and experimental studies of integer and noninteger singular light beams as well as speckle fields reported in the literature and analyzed using different approaches is presented.