Sets Of Interference Fringes Research Articles

Real-time quantitative phase imaging by single-shot dual-wavelength off-axis digital holographic microscopy.

A single-shot dual-wavelength digital holographic microscopy with an adjustable off-axis configuration is presented, which helps realize real-time quantitative phase imaging for living cells. With this configuration, two sets of interference fringes corresponding to their wavelengths can be flexibly recorded onto one hologram in one shot. The universal expression on the dual-wavelength hologram recorded under any wave vector orientation angles of reference beams is given. To avoid as much as possible the effect of zero-order spectrum, we can flexibly select their carry frequencies for the two wavelengths using this adjustable off-axis configuration, according to the distribution feature of object's spatial-frequency spectrum. This merit is verified by a quantitative phase imaging experiment for the microchannel of a microfluidic chip. The reconstructed phase maps of living onion epidermal cells exhibit cellular internal life activities, for the first time to the best of our knowledge, vividly displaying the progress of the nucleus, cell wall, cytoskeleton, and the substance transport in microtubules inside living cells. These imaging results demonstrate the availability and reliability of the presented method for real-time quantitative phase imaging.

Asymmetrically infiltrated twin core photonic crystal fiber for dual-parameter sensing

We demonstrate a fiber-optic dual parameter sensor based on a water filled Mach–Zehnder interferometer. Such a sensor is fabricated by asymmetrically infiltrating a twin core photonic crystal fiber with water, and splicing it between single mode fibers. Two sets of interference fringes which result from multi-mode interference are obtained by such a structure. By measuring the wavelength shift of the small fringe and the big envelop of the spectrum, strain and temperature can be determined simultaneously.

A Dichromatic Interference Intensity Modulation Approach to Measurement of Lubricating Film Thickness

The study aims to extend the measurement range of dichromatic interferometry in lubricating film thickness measurement. Subtraction of two sets of interference fringes, which are produced by dichromatic (red and green) lights, gives a modulated signal of intensity against film thickness. The measuring range without wavelength ambiguity is limited to the first half-cycle of the beat wave in the modulated signal. Theoretical and experimental analyses of the modulated interference intensity variation against film thickness were conducted. The differences in the pattern of the modulated interference intensity were obtained in the first three half-cycles of the beat wave. Based on that, a robust dichromatic interference intensity modulation approach for lubricating film measurement was derived and its measuring range without wavelength ambiguity was successfully extended to the magnitude equivalent to three half-cycles of the beat wave. To test the feasibility and credibility of this approach, the film thickness in elastohydrodynamic and hydrodynamic lubricated contacts was measured. The results were well correlated with the classical theory. Using red and green lasers with wavelength of 653 and 532 nm, respectively, the measurement range can be extended to 4 μm.

Deep 3D Optical Metrology

Confocal technique and white light interferometry have demonstrated to be suitable for characterization of transparent thick films. Layer's thickness and 3D topographies of its upper and lower interfaces can be determined from the two peaks in the confocal axial response or from the two sets of interference fringes developed during a vertical scan. Refraction index mismatch between immersion medium and layer worsens the performance of these techniques when profiling lower surface.

Simultaneous measurement of changes in thickness and refractive index of weakly absorbing self-standing solid films using optical interferometry

A nondestructive optical interferometric method, which enables a direct and simultaneous measurement of small changes in both thickness and refractive index of thin films, is described. Optical interferometric methods are sensitive to the changes in the optical path length (the product of the refractive index and the physical thickness) through the film. Thus, when the film is subjected to changing environmental conditions such as changing temperature or humidity, it is a challenge to determine the change in thickness and the change in refractive index separately, using interferometry. By simultaneously monitoring two different sets of interference fringes, i.e., transmission and reflection fringes, we have been able to successfully address this challenge. Our measurements on well-characterized pedigree glass samples are presented. The results agree well with the expected values for these samples, supporting the feasibility of this characterization technique to new materials. Self-standing, transparent (weakly absorbing) films ranging in thickness from tens to hundreds of microns can be characterized from direct measurements.

Signal Processing Using Laser Speckle Technique

Laser speckles has been widely used as a carrier of information. Speckle pattern resulting from the interference of random scattered coherent light from an optically rough object, has been used by many authors as a medium that can code different information. Image multiplexing using a laser speckle photography technique is capable of taking two or more exposures on the same holographic plate, with translation of the plate between exposures. In this paper an extraction of three multiplexed signals using random diffuser as a carrier is presented. Interference fringes obtained displaying each signal. The detection of the difference between two images has been applied using the same technique, in the recording step for two-signal multiplexing, the double exposure speckle photography technique has been appliec for each signal a certain displacement between exposures. Two sets of interference fringes can be obtained, each displays the information of each signal. While in the filtering step the minimum fringes were allowed to pass and the difference between the two signals can be detected instead of using the maximum fringe pattern.

Geometric phase analysis of high-resolution electron microscopy images of antiphase domains: Example Cu3Au

Abstract A new method for analysing antiphase domains using high-resolution electron micrographs is described. A high-resolution electron microscope image taken at a zone axis is treated as the sum of many sets of interference fringes. The analysis extracts the information concerning the variations in the image periodicities as a function of position. In particular, the amplitude and phase variations of these fringes are analysed separately. The amplitude images reveal the antiphase boundaries in a similar way to a conventional dark-field experiment whilst the phase produces images of the translation domains and defines the associated translation vectors. The phase variations can also be related to the strain field associated with the corresponding lattice planes. Experimental images of antiphase boundaries in Cu3Au taken at [001] are used to demonstrate the technique. Antiphase boundaries perpendicular and parallel to the electron beam are characterized. The phase images are used to characterize disorder...

Contrast enhancement of pulsed ESPI addition fringes

In this paper, the contrast enhancement produced by the subtraction of two sets of double pulse electronic speckle pattern interferometry (ESPI) addition fringes is investigated. It is shown that in most practical cases this process will produce a second set of interference fringes in addition to those which can be directly related to the vibration mode of interest. The formation of this second fringe pattern is explained by theory and computer simulation. Finally, the results are verified using an ESPI system with a pulsed Nd: YAG laser.

Reflection-interference method to determine droplet profiles

An optical method is developed to determine the instantaneous profile near the contact region of a minute droplet evaporating on a horizontal plate. A parallel coherent beam is split into two rays: one directed on the droplet at an oblique angle to the plate and the other passed through the droplet at a normal angle with the plate. The former produces a set of interference fringes by the light beams reflected from the droplet surface. Simultaneously, the latter creates a shadowgraph of the droplet on a screen. The liquid–vapor interfacial profile can be determined from the fringe patterns utilizing the droplet size on the plate calculated from its image on the shadowgraph. In addition, the contact angles can be uniquely defined and determined from the droplet profile.

On The Strength of Adhesive Bonds Between Rigid, Non-Crystalline Polymers

Abstract The relatively high strengths exhibited by well-prepared, rigid adhesive bonds partly reflect the crack-growth inhibiting properties of the surrounding bulk. Dispersion forces alone are unable to inhibit crack growth significantly, as is indicated, for example, by the low strengths of low molecular weight glassy polymers. The source of crack-growth inhibition of adhesive bonds was revealed by examining crack fronts with a microscope. Examined were crack fronts along the self-bond between pieces of poly(methyl methacrylate) and along the adhesive bond between pieces of poly(methyl methacrylate) and polystyrene. Associated with each crack front were two sets of interference fringes, indicating the presence of a craze preceding the crack. Crazes form in high molecular weight brittle polymers, and their presence along the adhesive bond ahead of the crack indicates the involvement of the high molecular weight bulk polymer adjacent to the bonding plane. Crazes ahead of cracks are known to inhibit fract...

An Elementary Theoretical Approach to the Abbe Theory of Optical Image Formation

An approach to the Abbe theory using only fairly simple mathematics is presented. The approach was originally developed for use in training students preparing for the graduateship examination of the Institute of Physics. Regarding the image as a set of interference fringes, it is shown from considerations of coherence that (a) the fringes are localized in the true image plane, and (b) that the faithfulness with which the object is imaged improves as the number of diffraction orders passing through the system is increased.

The Profiles of Chromospheric H and D3 from Interferometric Observations

Five plates showing the chromospheric D 3 and H α lines as sets of interference fringes are analysed by Treanor's method (16). This reduction, for the lowest 3000 km in the chromosphere, gives a D 3 profile which shows no systematic change with height (intensities normalized) and an H α profile whose broadening decreases from 1.15 A at 200 km to 0.795 A at 3200 km. It is supposed therefore that the H α line is broadened in part by self-absorption, and a method of eliminating this is described. Assuming that the significant contributions to the H α and D 3 emissions come from the same regions in the chromosphere, it is deduced from a comparison of the resultant helium and hydrogen Doppler profiles that the turbulent velocity is about 16 km/sec and that, though the temperature cannot be accurately determined, it is probably higher than that of the photosphere.

The calibration of disc recordings by light-pattern measurements

The paper sets out an analysis, in terms of geometrical optics, of the Buchmann-Meyer, or light, pattern which is formed by reflection from the modulated grooves of a recorded tone-disc. The pattern is considered as lying in the focal plane of the circular groove walls and not on the disc surface, as is usually assumed. A new apparatus for measuring the width of the patterns is described and the errors in disc-surface and focal-plane measurements found when using it are compared. The latter results are shown to possess the higher degree of consistency and their correctness is confirmed by an examination of the pattern formation in terms of physical optics. The origin of two sets of interference fringes which are visible in the patterns is also described. The decrease of luminous intensity which occurs at the edge of the patterns is then computed and it is shown that the new method of measurement described should give a higher degree of accuracy than hitherto available, even under some practical conditions when the edge of the pattern is not sharply defined.

The calibration of disc recordings by light-pattern measurements

The paper sets out an analysis, in terms of geometrical optics, of the Buchmann-Meyer, or light, pattern which is formed by reflection from the modulated grooves of a recorded tone-disc. The pattern is considered as lying in the focal plane of the circular groove walls and not on the disc surface, as is usually assumed. A new apparatus for measuring the width of the patterns is described and the errors in disc-surface and focal-plane measurements found when using it are compared. The latter results are shown to possess the higher degree of consistency and their correctness is confirmed by an examination of the pattern formation in terms of physical optics. The origin of two sets of interference fringes which are visible in the patterns is also described. The decrease of luminous intensity which occurs at the edge of the patterns is then computed and it is shown that the new method of measurement described should give a higher degree of accuracy than hitherto available, even under some practical conditions when the edge of the pattern is not sharply defined.

Multiple Sets of Fringes in the Michelson Interferometer

By using an unsilvered dividing plate in a Michelson interferometer or an intense source with the usual half-silvered plate several groups of interfering rays are produced due to internal reflections in the dividing and compensating plates. These lead to four distinct sets of interference fringes whose shapes change with variations of the distances and angles between plates and mirrors. They are circles, ellipses, straight lines and double sets of hyperbolas.