Using minimum deviation of a secondary rainbow and its application to water analysis in a high-precision, refractive-index comparator for liquids

A new method for measuring the refractive-index difference of a liquid has been developed. The liquid to be measured is contained in a 60-mm-diameter, cylindrical glass cell, and a He-Ne laser light is passed into the cell so that the laser light incidence fulfills the condition of minimum deviation. In this condition, the beam emerging from the cell has a fine interference fringe. The position of the interference fringe is read out as a marker to measure the deflection of the laser light. Directly reading the peak shift of the interference fringe makes it easy to obtain the refractive index difference of the liquid with a fairly high precision of at least 6 x 10(-6). Further high precision is potentially expected to be realized by use of an improved data analysis treatment of the overall interference fringe pattern.     

Two-beam interferometer for measuring aberrations of optical components with axial symmetry

We present a concept of interferometric testing, believed to be novel, that can be applied to measuring aberrations of optical components that have rotational symmetry. The optical configuration uses two coherent, collimated wave fronts that are tilted to impinge upon the optical component being tested such that one beam is on axis and the other is off axis. For small tilt angles the two aberrated wave fronts can be considered to be carrying the same aberrations. Furthermore, the off-axis beam is displaced along a direction orthogonal to the optical axis of the component. Interference between the two aberrated wave fronts produces a fringe pattern that is similar to a lateral shear interference pattern. Moiré fringes are obtained by spatial beating of the interference pattern with a CCD TV camera array. Under such conditions it is possible to subtract most of the linear carrier that is intrinsically present in the resultant fringe pattern owing to the large defocus aberration and tilt.     

Evaluation of the luminous flux intensity in a double-beam interferometer

Conclusion The luminance of the interference pattern in the plane of the photodetector slot can be determined by using the value of the luminous energy received through the input diaphragm for computing the attenuation of the luminous flux transmitted through the interferometer system. The half width of the utilized spectral line affects both a reduction in the fringe contrast with a rise in the interference-beam path-length difference and the total luminous intensity of the interference pattern. The photodetector slot which picks out a segment of the interference fringe produces definite conditions for modulating the luminous flux incident to the photomultiplier.Translated from Izmeritel'naya Tekhnika, No. 12, pp. 5–7, December, 1966.     

Bayesian neural-networks-based evaluation of binary speckle data

We present a new method using Bayesian probability theory and neural networks for the evaluation of speckle interference patterns for an automated analysis of deformation and erosion measurements. The method is applied to the fringe pattern reconstruction of speckle measurements with a Twyman-Green interferometer. Given a binary speckle image, the method returns the fringe pattern without noise, thus removing the need for smoothing and allowing a straightforward unwrapping procedure and determination of the surface shape. Because no parameters have to be adjusted, the method is especially suited for continuous and automated monitoring of surface changes.     

Thanks to 2012 Reviewers

The projector is designed to present a photoelectric scan of an interference fringe pattern together with a fiducial pulse as cathode-ray oscilloscope traces. Using alignment of the two traces as a setting criterion the position of fringes within an interferogram may be evaluated to better than 1/50 of the fringe period. The projector is able to make measurements from two-beam interferograms of low contrast and varying periodicity.     

Determining small angles of beam splitter rotation in optical vortex shearing interferometer

It is suggested to use a singular beam of unit topological charge in a scheme of vortex shearing interferometer intended for the observation of isoclinic fringes. In the interference pattern, the regions of fringe splitting determine the localization of wavefront dislocations and exhibit a shift that depends on the beam splitter rotation angel. Using the proposed method, it is possible to evaluate small angles of beam splitter rotation with an accuracy determined by the interference fringe width.     

Pulse-laser electroholography by use of interference fringe patterns captured by a CCD

Digital holography is combined with a pulse-laser electroholographic system for a real-time three-dimensional display. Owing to the one-dimensional characteristics of the Bragg-regime acousto-optic spatial-light modulator, vertical parallax cannot be generated from the acoustic signal propagating along the fan-shaped beam direction of the incident laser. To obtain a proper interference pattern, we attach a horizontal slit to the confocal lens system for recording the fringe data, significantly reducing the bandwidth of the vertical fringe data. When the bandwidth-reduced fringe data are displayed by use of a pulse-laser electroholographic system, the clarity and the quality of the image are found to be appreciably improved.     

Microinterferometry: Three-Dimensional Reconstruction of Surface Microtopography for Thin-Film and Wetting Studies by Reflection Interference Contrast Microscopy (RICM)

We present an improved theory of image formation by reflection interference contrast microscopy (RICM) for structural studies of stratified films on planar substrates and propose a new theoretical approach to analyzing the surface profile of nonplanar films. We demonstrate the validity of the new approach by analyzing the fringe patterns of RICM images from wedge-shaped liquid films and spherical probes. By simulation of various scenarios, we study the effect of finite-aperture illumination and the shape of the nonplanar interface on the interference fringe pattern of RICM images. We show how the reconstruction of the microscopic topography of the sample from the fringe spacing is corrected by angular and curvature correction terms. We discuss the variation of the mean intensity of the fringe patterns and the decay in the fringe amplitude with increasing fringe order that is caused by nonplanar interfaces of different slope.     

Measurement of a fiber-end surface profile by use of phase-shifting laser interferometry

We describe a laser interferometric system in which two objectives are used to measure surface profile on a connectorized fiber-end surface. By the use of the proposed illumination design a He-Ne laser as a point light source is transformed to an extended light source, which is beneficial to localize interference fringe pattern near the test surface. To obtain an optimal contrast of the interference fringe pattern, the flat mirror with an adjustable reflection ratio is used to suit different test surfaces. A piezoelectric transducer attached on the reference mirror can move precisely along the optical axis of the objective and permits implementation of four-step phase-shifting interferometry without changing the relative position between the CCD sensor and the test surface. Therefore, an absolutely constant optical magnification can be accurately kept to capture the interference fringe patterns resulting from a combination of light reflected from both the reference flat mirror and the test surface. The experimental result shows that surface profile on a fiber-end with surface features such as a small fiber diameter of 125 microm and a low reflection ratio of less than 4% are measurable. Measurements on a standard calibration ball show that the accuracy of the proposed setup is comparable with that of existing white-light interferometers and stylus profilometers.     

Measurement of in-plane and out-of-plane displacements and strains using digital holographic moiré

The paper proposes a non-destructive method for simultaneous measurement of in-plane and out-of-plane displacements and strains undergone by a deformed specimen from a single moiré fringe pattern obtained on the specimen in a dual beam digital holographic interferometry setup. The moiré fringe pattern encodes multiple interference phases which carry the information on multidimensional deformation. The interference field is segmented in each column and is modeled as multicomponent quadratic/cubic frequency-modulated signal in each segment. Subsequently, the product form of modified cubic phase function is used for accurate estimation of phase parameters. The estimated phase parameters are further utilized for direct estimation of the unwrapped interference phases and phase derivatives. The simulation and experimental results are provided to validate the effectiveness of the proposed method.     

Interference of Acoustically Phase-modulated Light Transmitted by a Semi-transparent Film with a Slit Opening

Spatial interference of acoustically phase-modulated light is explained experimentally and theoretically. If the acoustically phase-modulated light is transmitted by a semi-transparent sheet film with a slit opening, the light diffracted by the slit opening is superposed on the undiffracted background light in the Fresnel diffraction region to yield an acoustically modified interference pattern. This pattern is successfully explained as a result of the partially coherent illumination which is due to acoustic wave modulation. An application of this method is described for measurements of the Raman-Nath parameter and the acoustic wavelength from the variational aspect of the interference fringe pattern.     

Theory of Ultra-high-resolution Optical Raman Ramsey Spectroscopy

A non-perturbative theoretical analysis of Ramsey interference lineshapes in three-level lambda systems excited by laser fields has been developed for the general case of several interaction regions. In conventional Ramsey excitation, two laser fields excite the lambda system each in two separate spatial interaction regions. Here we examine how increasing the number of interaction regions or altering the interaction times change and improve the lineshape characteristics such as fringe visibility. For short interaction times the fringe pattern is strongly dependent on the number of interaction regions, with the n = 2 sinusoidal fringes replaced by sharper fringes of greater visibility. With larger interaction times, the fringe pattern is virtually unchanged on increasing the number of interaction regions. The optimum fringe pattern is obtained with short interaction times and a larger (n a 9) number of regions.     

Vibration-compensated interferometry system using phase-modulating interference fringe subdivision technology

An innovative vibration-compensation method, with phase-modulating interference fringe subdivision technology, is described. It simulates fringe movement by the phase difference of signals and can detect the fringe movement with an accuracy of 1/400 fringe spacing using this subdivision technology. A closed-loop vibration-compensation system is built, and the measurement of an interference fringe movement and a vibration-compensation test are successfully demonstrated. Because of this new method and a new feedback algorithm that was introduced, interference fringes can be stabilized at any preset phase position in real time. Compared with known methods, this method is simple and inexpensive, as well as effective.     

Analysis of capillary interferometry for measuring refractive indices of minute samples

A method of measuring the refractive indices of minute samples by analyzing capillary interferometry is introduced. With the interference theory of light, the intensity distribution of an interference fringe pattern formed by a cylindrical tube of a capillary is obtained, and the influence of some parameters on the fringes are discussed. The measurement accuracy and its relative problems are analyzed.     

条纹图形Heusler合金CoFeMnSi薄膜的制备及其磁特性研究

以CoFeMnSi作为研究对象,对其进行图形化设计,以研究图形化CoFeMnSi薄膜的磁学特性。利用感光溶胶-凝胶法和激光干涉法制得条纹图形ZrO2薄膜,之后利用磁控溅射法在其表面溅射沉积CoFeMnSi,以达到制得图形化CoFeMnSi磁性薄膜的目的,并对其表面形貌和磁学特性进行了表征。采用金相显微镜分析验证CoFeMnSi薄膜继承了ZrO2的条纹图形结构,条纹图形周期约为2μm;面内磁性测量显示薄膜398 kA/m磁场下的磁化强度与外磁场和条纹夹角θ呈180°周期性变化关系,且磁化强度介于390~440 kA/m;利用CoFeMnSi平膜面内磁化强度及面外磁化强度与外加磁场方向的变化关系,解释了条形薄膜磁化强度的θ角度依赖关系;采用磁力显微镜观察到磁畴结构形态为蜂窝状,磁畴尺寸大约1~2μm。     

Interferometric analysis of reorientational nonlinear phenomena at 10.6 microm in a nematic liquid crystal

We describe an infrared interferometric technique based on a two-dimensional spatial fringe analysis Fourier method for investigating the characteristic ring diffraction pattern generated by the self-phase-modulation effect induced in nematic liquid crystals (NLCs) by an infrared laser beam and for measuring the nonlinear refractive index of the NLCs. The experimental setup employs a Mach-Zehnder interferometer with a cw CO2 laser emitting at 10.6 microm and a pyroelectric optoelectronic sensor matrix to detect the modulated ring-pattern intensity distribution formed in the far field by a nematic E7 sample. A Fourier-transform-based analysis of the interference fringe pattern allows comparison of the measurements with the theoretical ring-pattern intensity distribution. We show that accurate determination of the nonlinear refractive index can be obtained by analyzing the two-dimensional phase distribution of the modulated ring pattern.     

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.     

Reversible interference fringe counter with a small measurement range

Conclusions On the basis of the above work we assembled an apparatus with an interference fringe counter which had a range of 50 fringes and a precision down to one interference fringe. The utilization of a single-stage photomultiplier type FÉU-2 made it possible to produce a counter which has a small measuring range and does not require a high voltage source. The displacement of one interference fringe system with respect to the other by half a period was attained, owing to the small number of fringes, by a simple adjustment of the slit positions. The electronic unit can also be used for measuring larger displacements, provided the number of counting cells is increased and the interference fringes fed to the photomultiplier have a sufficient brightness and contrast.     

Three-dimensional profilometry based on shift estimation of projected fringe patterns

This paper presents a new approach to fringe pattern profilometry. In this paper, a generalized model describing the relationship between the projected fringe pattern and the deformed fringe pattern is derived, in which the projected fringe pattern can be arbitrary rather than being limited to being sinusoidal, as are those for the conventional approaches. Based on this model, what is believed to be a new approach is proposed to reconstruct the three-dimensional object surface by estimating the shift between the projected and deformed fringe patterns. Additionally, theoretical analysis, computer simulation, and experimental results are presented, which show how the proposed approach can significantly improve the measurement accuracy, especially when the fringe patterns are distorted by unknown factors.