Analysis of Lau interferometric fringe for measurement of focal length by using wavelet filtering techniques

New filtering scheme is investigated and implemented on Lau interferometric fringes to enhance the signal-to-noise ratio (SNR) in the Lau interferograms. Towards this, the applicability of Haar, Daubechies and Symlet wavelet based filtering schemes have been tested. Of these schemes, the Symlet based filtering scheme gives the best results in terms of improved signal to noise ratio and speckle index. This scheme is then used to analyse Lau interferograms recorded in the experimental arrangement for focal length measurement. The processed interferograms yield improved accuracy and precision of measurement.     

A simple phase unwrapping approach based on filtering by windowed Fourier transform: A note on the threshold selection

A simple phase unwrapping approach based on windowed Fourier filtering was proposed recently [K. Qian et al. A simple phase unwrapping approach based on filtering by windowed Fourier transform. Opt Laser Technol 2005;37:458–62]. The windowed Fourier filtering algorithm is an essential ingredient that suppresses the noise effectively and makes the phase unwrapping trivial. This paper adds a note on the threshold selection in the windowed Fourier filtering algorithm. A large interval can be selected as the threshold to obtain almost optimal filtering results. Once the selected threshold is suitable, it is almost optimal. This makes the threshold selection in the windowed Fourier filtering algorithm extremely easy.     

Application of digital speckle pattern interferometry and wavelet transform in measurement of transverse vibrations in square plate

In this paper the study of out-of-plane or transverse vibrations in a square plate using digital speckle pattern interferometry (DSPI) is presented. To improve the measurement accuracy, we have implemented a new filtering scheme based on combination of average/median filtering and Symlet wavelet filtering which enhances the signal to noise ratio in the speckle interferogram obtained from DSPI. A large number of fringe patterns are shown for square plate with two different boundary conditions. Experimentally obtained resonance frequencies for the square plate for the boundary condition one edge fixed and other edges being free, the resonance frequencies obtained from DSPI show good agreement with that obtained from classical theory for thin plates.     

Measurement of out-of-plane static and dynamic deformations by processing digital speckle pattern interferometry fringes using wavelet transform

In this paper, we are presenting measurement of static and dynamic deformations in rectangular plate fixed at one end using digital speckle pattern interferometry (DSPI). To improve the measurement accuracy, we have developed a new filtering scheme based on combination of average/median filtering and Symlet wavelet filtering which enhances the signal-to-noise ratio (SNR) in the speckle interferogram obtained from DSPI. Experimental results show that our filtering scheme is quite effective in improving SNR of the speckle interferogram. The measurements by DSPI and calculations from beam theory in the case of out-of-plane static deformation and the measurements by DSPI and accelerometer in the case of dynamic deformation are in good agreement.     

Theoretical model for the transverse interference pattern of GRIN optical fiber using a laser sheet of light

A new technique (El-Ghandoor et al., Opt. Laser Technol. 31(7) (1999) 481–488) has been applied to study the shape of transverse interference fringes, instead of multiple beam Fizeau fringes (Marhic, Stein, Appl. Phys. Lett. 35 (1975) 1678–1682), from a GRIN optical fiber. In this technique, a laser light sheet is used to illuminate and pass directly through the optical fiber. Theoretical expressions are derived for the optical path differences of three groups of interference beams. The first one passes through the cladding, the core, and then the cladding once again; the second passes through the cladding only, and the third passes through the surrounding air. Theoretical expressions for the shape of transverse interference fringes formed across isotropic non-absorbing optical fibers are also calculated.     

Application of wavelet filtering techniques to Lau interferometric fringe analysis for measurement of small tilt angles

This communication presents the results of investigation undertaken towards testing the viability of wavelet filtering techniques in analyzing the Lau interferometric fringes. Towards this, the applicability of Haar, Daubechies and Symlet wavelet based filtering schemes have been tested. Of these schemes, the Symlet based filtering scheme gives the best results in terms of improved signal to noise ratio. This scheme is then used to analyze Lau interferograms recorded in the experimental arrangement for tilt angle measurement. The processed interferograms yield improved accuracy and precision of measurement.     

相干激光雷达图像散斑噪声抑制算法

提出了一种新的用于散斑噪声抑制的非线性加权均值多方向形态滤波算法。运用此算法和先前提出的散斑噪声抑制算法以及小波软阈值算法和Lee滤波算法一并对相干激光雷达图像进行了噪声抑制处理，并且对处理的结果进行了比较，证明了本算法的进步，即在不降低噪声抑制能力的前提下，较好地保持了图像边缘。     

Polarized Multiply Scattered LIDAR Signals

In this paper we shall present our stochastic model for the transfer of polarized light. We introduce the polarized phase function which is necessary for the exact determination of the scattering distribution for polarized light. Finally, we compare results of variance reduction Monte Carlo simulations based on that model with measurements taken with the DLR-Microlidar. This LIDAR is designed especially for cloud and fog measurements and has two fields of view with two polarization channels each; see W. Krichbaumer et al. (Opt. Laser Technol. 25 (1993) p. 283).Presented at the 7th International Workshop on Multiple Scattering Lidar/Light Experiments (MUSCLE7), July 21–23 1994, Chiba, Japan.     

激光显示中消散斑方案研究

激光显示消散斑问题是激光显示的重要研究课题,是阻碍激光显示真正实用化的一个关键难题。综述了国内外已有的消散斑方案的优劣以及可行性,并重点分析了双屏幕振动消散斑方案。在此基础上,提出了新的三种理论消散癍方案：铁电液晶消散斑,波导扰动光纤消散斑和旋转散射片消散斑。     

Cryptanalysis and improvement of multiparty quantum secret sharing schemes

A scheme of multiparty quantum secret sharing of classical messages (QSSCM) [Z.J. Zhang et al., Opt. Commun. 269 (2007) 418] was proposed. Lin et al. [S. Lin et al., Opt. Commun. 281 (2008) 4553] showed the last agent can obtain half of the secret in Z.J. Zhang's et al. three-party QSSCM scheme and gave an improved version. We further show the first agent and the last agent can obtain all the secret without introducing any error in Zhang's et al. multiparty QSSCM scheme by a special attack with quantum teleportation. We also present an improved version.     

Information leakage in three-party simultaneous quantum secure direct communication with EPR pairs

In 2007, Wang et al. [M. Y. Wang and F. L. Yan, Chin. Phys. Lett. 24 (2007) 2486] proposed a three-party simultaneous quantum secure direct communication (3P-SQSDC) scheme with EPR pairs. Recently, Chong et al. [S. K. Chong and T. Hwang, Opt. Commun. OPTICS-15438 (2010(online))] proposed an enhancement on Wang et al.'s scheme. The communications in Chong et al.'s 3P-SQSDC can be paralleled and thus their scheme has higher efficiency. However, we find that both of the schemes have the information leakage, because the legitimate parties' secret messages have a strong correlation. This kind of security loophole leads to the consequence that any eavesdropper (Eve) can directly conjecture some information about the secrets without any active attack.     

Spatial filtering of holographic interferograms of lateral shift

With the Fresnel approximation we consider the formation of lateral shift interferograms in diffusely scattering fields during double-exposure recording of Fresnel holograms of a dull screen on the basis of superposition of the objective speckle fields of the two exposures in the plane of the photographic film. It is shown that the interference pattern characterizing the phase distortions of the wave front of radiation, used to illuminate the dull screen, is located in its imaging plane, while the front of the supporting wave is located in the hologram plane. To record them it is necessary to carry out spatial filtering of the diffraction field in the corresponding planes.V. V. Kuibyshev Tomsk State University. Translated from Izvestiya Vyssikh Uchebnykh Zavedenii, Fizika, No. 8, pp. 106–111, August, 1994.     

2D single-shot imaging of OH radicals using tunable excimer lasers

Three schemes for imaging OH with tunable excimer lasers are compared: Excitation and detection at 308 nm (0–0 band, XeCl laser), excitation with a KrF laser at 248 nm (3–0 band) and a new scheme using excitation at 308 nm and detection at 343 nm (0–1 band). Each scheme has certain advantages: The first scheme gives by far the highest signal, the second is less sensitive to collisional quenching and the third is suited to dirty environments because of the long excitation wavelength and off-resonance detection.     

Measurement of angular dependence of M X-ray production cross-sections in Re,Bi and U at 5.96 keV

The M X-ray production differential cross sections in Re, Bi and U elements have been measured at the 5.96 keV incident photon energy in an angular range 135°–155°. The measurements were performed using a ⁵⁵Fe source and a Si(Li) detector. The present results contradict the predictions of Cooper and Zare [Atomic Collision Processes, Gordon and Breach, New York (1969)] and experimental results of Kumar et al. [J. Phys. B: At. Mol. Opt. 34, 613 (2001)]. that, after photoionization of inner shells, the vacancy state has equal population of magnetic substates and the subsequent X-ray emission is isotropic, but confirm the predictions of the calculations of Flügge et al. [Phys. Rev. Lett. 29, 7 (1972)] and experimental results of Sharma and Allawadhi [J. Phys. B: At. Mol. Opt. 32, 2343 (1999)] and Ertugrul [Nucl. Instrum. Meth. B 119, 345 (1996)]. Total M X-ray production cross sections from the decay at the 5.96 keV photon energies are found to be in good agreement with the calculated theoretical results using the theoretical values of M shell photoionization cross section.     

Numerical simulations on the formation of laser speckles with nanofluids

Our recent work revealed that speckles can be formed when nanofluids containing a proper volume fraction of nanoparticles are illuminated by a monochromatic laser beam [Qian M, Liu J, Yan M-S, Shen Z-H, Lu J, Ni XW, et al. Investigation on utilizing laser speckle velocimetry to measure the velocities of nanoparticles in nanofluids. Opt Express 2006; 14: 7559–66]. In this paper, two different physical models are established to figure out the speckle-formation mechanism. The photon–nanoparticle-collision model emphasizes the random collisions between photons and nanoparticles, and Monte Carlo method is used to simulate how the incident photons move in the vessel containing nanofluids. However, in the electric-dipole model, each illuminated nanoparticle becomes an electric dipole and sends out scattering lights, and the coherent addition of the scattering lights from nanoparticles is numerically calculated. Finally, from the numerical results, the speckle-formation mechanism is figured out.     

Measurement of dynamic crack tip displacement field by speckle photography and interferometry

Speckle interferometry has been used to measure the transient displacement field around a crack due to stress wave loading. Double exposure interferograms are recorded with a pulsed ruby laser, and correlation fringes formed by spatial filtering of the developed film. A new technique is presented for reducing the noise level in spatially filtered speckle interferograms. Independent fringe patterns, obtained from one interferogram but with the filtering aperture sampling different regions of the Fourier transform plane, are digitised by a CCD camera and combined numerically. It is demonstrated that accurate analysis of fringe patterns by the Fourier transform method can be carried out, even if no carrier fringes are present. The measurements are compared with those obtained by speckle photography. Least-squares fitting of the theoretical displacement field is used to calculate the stress intensity factor at the crack tip as a function of time.     

Experimental requirement of the error-compensating five-frame interferogram-collecting sequence used in phase-shifting interferometry

Digital phase-shifting interferometry (PSI), a technique widely used in optical testing, requires interferograms collected at optical phase differences separated by a definite phase step. The five-frame interferogram-collecting sequence suggested by Hariharan et al. [Appl. Opt. 26, 2504 (1987)] is extremely effective in significantly reducing the errors in height profiles derived using PSI that are caused by phase-step errors. In this Letter, we report on a class of five-frame sequence that, owing to its mathematical equivalence with the one suggested by Hariharan et al. and its ease of execution, is more commonly used but is much less effective in reducing the height profile errors caused by phase-step errors.     

Vector modes of rectangular-core dielectric waveguides: An improved perturbation approach

We present an improved analysis to obtain vector modes of a rectangular-core waveguide (RCW) structure whose dielectric constant profile is separable in x and y coordinates. Using this analysis, a perturbation method is then developed to obtain vector modes of a practical RCW. The propagation constants so obtained for a fully-buried and a ridge RCW structure using the present analysis are found to be in better agreement with reported numerical values than the ones obtained with an earlier reported perturbation approach [Kumar et al., Opt. Lett. 8 (1983) 63].     

Temperature field modeling during multi-modes CO2 laser irradiation of human enamel

We examine the temperature fields of human enamel [Yu D, Fox JL, Hsu J, Lynn Powell G, Higuchi WI. Computer simulation of surface temperature profiles during CO₂ laser irradiation of human enamel. Opt Eng 1993; 32(2)] during multi-modes CO₂ laser irradiation. For this we use the integral transform method as well as direct and inverse Laplace transform [Oane M, Sporea D. Temperature profiles modeling in IR optical components during high power laser irradiation. Infrared Phys Technol 2001; 42(1): 31–40; Oane M, Sporea D. Study of heat transfer in IR optical components during CO₂ laser irradiation. Proc SPIE 2001; 4430: 898–904; Oane M. Mathematical modeling of the thermal field distributions in solids under multiple laser irradiations. Proc SPIE 2003; 5227: 329–34; Oane M, Apostol I, Timcu A. Temperature field modeling in laser heated metals for laser cleaning of surfaces. Proc SPIE 2003; 5227: 323–8]. The enamel block is modeled as homogeneous cylinder in three dimensions. Results indicate that (i) the thermal field depends on multi-modes structure; (ii) heat transfer coefficient plays an important role in temperature distribution.     

Optical Haar Wavelet for Extracting Edge Features along Arbitrary Directions

A novel circular Haar wavelet (CHW), which is obtained by a radially distributed polarization state, is proposed. Optical wavelet transforms using the proposed CHW are implemented by computer simulations. The proposed CHW is shown to have remarkable features: (1) it is useful for detecting outlines of input images; (2) one polarization component is available for extracting an edge feature along a required direction; and (3) unlike the previously proposed CHW (Z. He and S. Sato: Opt. Lett. 19 (1994) 686), this one can be applied to a multi-resolution edge extraction (Y. Sheng, D. Roberge and H. H. Szu: Opt. Eng. 31 (1992) 1840).