Comment: Influence of illuminating beyond the object support on Zernike-type phase contrast filtering

In this comment, we clarify some serious misinterpretations that can arise from an uncritical use of the results presented in [Appl. Opt. 41, 2607, (2002)]. In particular, we point out that their suggestion of using "illumination beyond the object support" for measuring phase disturbances can result in distorted or strongly inaccurate interference patterns. We also point out that Llave and Castillo have misinterpreted our previous work describing the effect of phase object fill factor on the output interference patterns, which is in fact one of the key factors considered in the generalized phase contrast (GPC) method. Unlike the Zernike method, the GPC method results in an optimized visualization of the phase disturbance by the achievement of a matching condition between the applied filter and the spatial average of a given phase disturbance, thereby implying the optimal use of fill factor information.     

Phase filtering in nonlinear-imaging technique with a phase object

Using the nonlinear-imaging technique with a phase object (NIT-PO), we have studied third-order nonlinearities of various samples. In this work, we develop, for pure nonlinear refractive materials, an approximate method to calculate the nonlinear refractive coefficient analytically. By decomposing the object field passing through the phase object into two top-hat beams of different phases and beam radius, we acquire the approximate phase contrast, from which we extract the nonlinear refractive coefficient. This approximation is valid when the on-axis nonlinear phase shift by the sample is less than π. In addition, this approximation serves to estimate the sensitivity and monotonic interval for nonlinearity measurements more easily and thus helps us to maximize both the sensitivity and monotonic interval of measurements. We test this method with CS(2), a well-characterized third-order nonlinear refractive material using 21 ps laser pulses at 532 nm. We expect this method can be applied to high-order nonlinear refraction cases.     

Noise-residue filtering of interferometric phase images

The effect of noise-induced phase inconsistency on interferometric phase information content is studied. Phase inconsistencies, or residues, hinder a correct unwrapping of the phase signal. The probability of noise-induced phase inconsistencies is obtained as a function of the signal-to-noise ratio. Moreover, a two-dimensional noise-residue filter, intended to be applied as a preprocessing step before phase unwrapping, is proposed. The method is based on the observation that the noise creates adjacent phase inconsistencies mainly in interferometric phase images. A local analysis leads to a set of rules to be applied to reduce noise-induced phase inconsistencies. The filter performances are tested on noisy synthetic and real phase data.     

The effect of the phase of transmission on contrast agent echoes

Ultrasound contrast agents consist of a gas bubble, encapsulated by a shell for stabilization. The shell dampens the fluctuations in the bubble radius when insonified. The detection of contrast microbubbles during a medical examination can indicate whether a region is perfused with blood. Here, the authors consider the effect of the phase of sonification signal on the backscatter by the bubble echo. By transmitting two short pulses of ultrasound with opposite phases, the authors demonstrate that a unique pair of echoes can be generated by a single microbubble, and that the properties of these echoes may be useful in the discrimination of bubble and tissue echoes. Specifically, the significant echo amplitude begins coincident with each transmitted rarefactional half-cycle, and the mean frequency of this echo depends on the transmitted phase. When rarefaction is transmitted first for a 2.25 MHz signal, the mean frequency is 0.8 MHz higher for an albumin-shelled bubble and 0.9 MHz higher for a lipid-shelled bubble. The experimental results agree with the predictions of the Gilmore-Akulichev equation.     

Influence of geometry on polychromatic speckle contrast

Understanding speckle behavior is very important in speckle metrology application. The contrast of a polychromatic speckle depends not only on surface roughness and the coherence length of a light source, as shown in previous works, but also on optical geometry. We applied the Fresnel approach of diffraction theory for the free-space geometry and derived a simple analytical relationship between contrast, coherence length, size of illuminated spot, and distances between source, object, and observation plane. The effect of contrast reduction is found to be significant for low-coherence light sources.     

Inverse problem in the X-ray phase contrast method

An analysis is made of the possibility of solving the inverse problem of reconstructing the internal structure of an object using a set of experimental distributions measured in an x-ray beam for various orientations of the object. Pis’ma Zh. Tekh. Fiz. 25, 1–7 (February 12, 1999)     

Influence of properties of filtering liquids on the permeability of disperse systems

A method is proposed for determining the filtration characteristics of finely dispersed systems (clayey soils) through a calculation of their adsorption and rheological properties.Translated from Inzhenerno-Fizicheskii Zhurnal, Vol. 27, No. 6, pp. 1002–1008, December, 1974.     

Measurement of nanomovements of an object from the optical phase image

We examine a method for measuring small movements of an object, based on calculation of the displacement of the image obtained using an optical interferometer. We estimate the effect of phase noise in reconstruction of the coherent structure of the field on the accuracy in measuring the movements. We have made practical estimates of the displacements of the real object from phase image data. We compare the estimates with the results of direct measurements of the displacements. We show that it is possible to detect movements of less than 10 nm using a commercial microscope.     

Optical phase contrast measurement of ultrasonic fields

This report describes an optical phase contrast imaging technique for the measurement of wide bandwidth ultrasound fields in water. In this method, a collimated optical wavefront (λ_l = 810 nm) impinges on a wide bandwidth ultrasound pulse. The method requires that refractive index perturbations induced by the ultrasound field be sufficiently small. Specifically, on exit from the acoustic field, the phase of the optical wavefront must be proportional to the ray sum of local density taken in the direction of propagation of the incident optical wave. A similar restriction is placed on the dimensions of the ultrasound pulse. Repeated measurement of this phase as the ultrasound field is rotated through 180° about an axis normal to the direction of propagation of the incident optical wave generates the Radon transform of the ultrasonically induced refractive index perturbation. Standard tomographic reconstruction techniques are used to reconstruct the full three-dimensional refractive index perturbation. A simple two-lens imaging system and an optical signal processing element from phase contrast microscopy provide a method of directly measuring an affine function of the desired optical phase for small optical phase shifts. The piezo- and elasto-optic coefficients (the first partial derivatives of refractive index with respect to density and pressure) relate refractive index to density and pressure via a linear model. The optical measurement method described in this paper provides a direct, quantitative measurement of the piezo- and elasto-optic coefficients (from the density or pressure fields)     

Focal-plane detection and object reconstruction in the noninterferometric phase imaging

In this paper, we propose effective methods to detect focal planes and recover objects in the noninterferometric phase imaging. A strategy using different aberration coefficients is developed, and a series of diffraction intensity maps is sequentially recorded by a charge-coupled device. During numerical reconstruction, a phase retrieval algorithm is applied to extract object wavefront from diffraction intensity maps. Subsequently, numerical methods are proposed to detect focal planes, and high-quality phase maps are recovered by using the detected focal distances. Theoretical results are presented to demonstrate feasibility and effectiveness of the proposed methods.     

弯曲磁过滤电流对TiN膜质量的影响

为研究弯曲磁过滤弧离子镀工艺的磁过滤电流变化对薄膜质量的影响,用弯曲磁过滤弧离子镀工艺在3.0～4.5A内变化磁过滤电流制备了TiN薄膜样品,用扫描电子显微镜观察了薄膜表面与截面形貌,用X射线衍射研究了薄膜的组织结构,从等离子体角度分析了磁过滤电流对薄膜表面质量、结晶质量等薄膜质量及生长速率的影响.结果表明,引入磁过滤后,因去除大颗粒的结果使薄膜表面均很光滑,且表面大颗粒的尺寸与磁过滤电流的大小关系不大.当磁过滤电流为4.0A时,TiN薄膜结晶良好、膜基结合紧密,生长速率达到最大的1.1μm/h,且具有很强的[200]择优取向.在4.0A磁过滤电流下制备的TiN薄膜所呈现的质量特性是由于此电流下等离子体密度与能量高、基体的位置又正好处于聚集的等离子体区域中心.     

High-precision measurement of low reflectivity specular object based on phase measuring deflectometry

Phase measuring deflectometry (PMD) is a robust, noncoherent technique for the characterization of specular surface. For measuring high specular reflectivity surface, PMD can deliver micron radian range local gradient. However, when the measured surface has low specular reflectivity, the accuracy of the measured gradient is low since the captured fringe pattern shows low signal to noise ratio. The phase error characteristics in PMD system when testing low reflectivity surfaces are analyzed. The analysis illustrates that the random phase error increases rapidly while the nonlinear error drops slowly with the decreasing of the tested surface reflectivity. In order to attain high precision measurement of low reflectivity specular surface, a robust error reduction method based on wavelet de-noising is proposed to reduce the phase error. This error reduction method is compared with several other normally used methods in both simulation and experiment work. The method based on the wavelet de-noising shows better performance when measuring the low reflectivity specular surface.     

Reconstruction of a vibrating object from its time-averaged image intensities by the use of exponential filtering

We consider the reconstruction of a complex-valued object that vibrates in some out-of-plane modes. The reconstruction is based on the phase-retrieval method with the use of two intensity measurements: the two time-averaged image intensities of the object illuminated coherently, which are modulated in two Fourier-transform planes of the object by the use of two filters with exponentially decaying transmittances that complement each other. We discuss the necessary condition of the vibration for the reconstruction method. Computer-simulated examples of retrieving the phases of one-dimensional objects demonstrate that the reconstruction of a sinusoidal-vibrating and a Gaussian random-vibrating object can be treated by this method.     

Improving the quality of phase maps in phase object digital holographic interferometry by finding the right reconstruction distance

Improved quality of phase maps in pulsed digital holographic interferometry is demonstrated by finding the right reconstruction distance. The objective is to improve the optical phase information when the object under study is a phase object and when it is out of focus, leading to low contrast fringes in the phase map. A numerical refocusing is performed by introducing an ideal lens as a multiplication by a phase field in the Fourier domain, and then a region of maximum speckle correlation is found by comparing undisturbed and disturbed subimages in different refocused imaging planes. After finding the right reconstruction distance, a phase map of high visibility is constructed. By this technique a 30% reduction of the phase error for a flow of helium gas and a 50% reduction of the phase error for a weak thin lens were obtained, which resulted in a significant improvement of the visual appearance of the phase maps.     

Autofocusing in digital holographic phase contrast microscopy on pure phase objects for live cell imaging

Digital holography enables a multifocus quantitative phase microscopy for the investigation of reflective surfaces and for marker-free live cell imaging. For digital holographic long-term investigations of living cells an automated (subsequent) robust and reliable numerical focus adjustment is of particular importance. Four numerical methods for the determination of the optimal focus position in the numerical reconstruction and propagation of the complex object waves of pure phase objects are characterized, compared, and adapted to the requirements of digital holographic microscopy. Results from investigations of an engineered surface and human pancreas tumor cells demonstrate the applicability of Fourier-weighting- and gradient-operator-based methods for robust and reliable automated subsequent numerical digital holographic focusing.     

Theoretical study of amplitude and phase filtering of guided waves

The design of integrated optics filters by use of refinement software based on the Abelès thin-film computation method and the film mode matching method is studied. The results obtained with the two computation methods are compared. Good agreement is obtained provided that the fill factor of the guided mode in the component is high and that modal losses between waveguide sections are simulated by absorption with the Abelès computation method. Integrated optics devices that manage either the amplitude of guided waves such as a dense wavelength division multiplexing narrow-bandpass filter and a gain-flattening filter or the phase of guided waves such as a broadband dispersion compensator are     

Influence of linear equality constraints on object restoration in incoherent light

We investigate how prior knowledge of the object in the form of linear equality constraints influences the inverse problem of incoherently illuminated object reconstruction by using an elimination method in the context of least squares by regularized singular-value decomposition. Some representative numerical calculations that use noisy images were carried out to illustrate the analysis. When compared with the corresponding unconstrained inversion it appears that the linear constrained inverse does not seem to be any better when viewed in the global sense.     

Influence of the form of the illuminating beam upon the error of length measurements made with a laser-type Michelson interferometer

Conclusions By solving the problem of the interference of Gaussian beams, we obtained formulas for the calculation of the systematic error which is made when a laser-type Michelson interferometer is used to measure length. We gave recommendations on the geometrical dimensions of the Michelson interferometer and its matching to the laser radiation so that the above error is reduced. We have described the experimental verification of our formulas.Translated from Izmeritel'naya Tekhnika, No. 2, pp. 40–42, February, 1976.