Non-coherent noise reduction in digital holography based on root mean square technique

In this paper, the root mean square (rms) technique is applied in order to reduce the non-coherent noise in phase-contrast image. The proposed technique is applied to a sample of 200 μm step height nominally. The recorded off-axis interferograms generated from two different wavelengths are processed to obtain an object wave (amplitude and phase) for each wavelength separately. The independent phase maps are subtracted and a phase map for the beat-wavelength is obtained and converted to height map. The rms values of 10 pixels profiles from the obtained height map are calculated automatically to show the three-dimensional (3D) profile. The experimental results show that the non-coherent noise is reduced by the order of 90% when the rms technique is applied and the uncertainty in measurement has been found to be of the order of 1.5 μm. The proposed technique can provide a simple and real solution for measuring 3D objects having high abrupt height difference.     

Time-average holographic interferometry with a sinusoidally modulated laser diode

Laser diodes have the features of a single-mode operation and a frequency tunability. Holographic interferometry is described for investigating the vibrating amplitude and phase with a frequency-modulated laser diode. Sinusoidal wavelength change by varying laser injection current produces the sinusoidal phase modulation of relative phase difference between the reference and vibrating object paths. Holograms are made by time-average exposure of three-type recording modes with a laser diode. The phase of vibrating object is extracted from the measurements of Bessel-type fringe irradiances in three kinds of time-average holographic reconstruction. Experimental results of phase and amplitude for a vibrating cantilever object are shown.     

A.第十九届国际高速摄影和光子学会议概况

本文对第19届国际高速摄影与光子学会议做了简介,主要谈到了光机式相机、高速视频技术、全息和干涉计量。     

Displacement measurements in structural elements by optical techniques

Speckle metrology and holographic interferometry (HI) have been used in several civil engineering applications. We present the results obtained by applying speckle photography (SP) to the study of two quadratic shearwalls with different boundary conditions, and the potential of the technique in the study of this kind of structures is described. The analysis of Young's fringes obtained with this technique at certain points on each shearwall provides the whole field of displacement measurements. HI has been used to measure the three components of absolute displacement, verifying that the bulging phenomenon does not affect the in-plane components when the applied load remains on the same plane as the shearwall. A qualitative analysis is carried out following an electronic speckle pattern interferometry (ESPI) technique. The results obtained by optical techniques are compared to the numerical results obtained by the finite element method (FEM), finding good correlation between them in all the cases.     

Quantitative strain analysis of flip-chip electronic packages using phase-shifting moiré interferometry

In order to gauge the reliability of electronic packages, it is valuable to analyze thermally induced displacements and strains around bimaterial corners and within interconnections. The increased demand for computing performance has created increasingly complex electronic packages with miniaturized features, making it increasingly difficult to extract these quantities. Often, material properties at these length scales are not fully known, making modeling and simulation problematic. Thus, determining displacements and strains experimentally is attractive. In this study, an advanced flip-chip package with fine interconnection features was analyzed using phase-shifting moiré interferometry (PSMI) in conjunction with image analysis software developed for this purpose. Before the analysis, PSMI was qualified using an isotropic solid undergoing uniform thermal contraction, which yielded a displacement precision of ±4 nm. Then a high-magnification, high-resolution displacement and strain analysis was performed for a small cross-sectional region of the flip-chip package containing 20–100 μm sized features. The analysis quantifies these results and gives displacements and strains obtained by differentiating the displacement data using a strain-energy-based finite element formulation.     

Polarizing interferometer with constant radial and azimuthal shears

An interferometer is described in which a rotatable Wollaston prism is used to achieve constant radial and azimuthal shears in a converging beam. These displacements may have applications in speckle shearing interferometry for the deformation measurement of objects with axial symmetry.     

刚体位移对应变测试的影响

通过运用波前干涉理论,得到了贴片云纹干涉法测圆柱壳的位移与应变公式,分析了刚体位移及曲率对测试结果的影响情况.指出了在对压力容器及管道进行测试时应注意的事项.     

Electronic speckle pattern interferometry analysis of tensile tests of semihard copper sheets

Uniaxial tension tests of semihard copper sheets were studied by means of electronic spekle pattern interferometry (ESPI). The setup allowed the authors to analyze in detail the transitions from elastic to plastic behavior and from homogeneous to inhomogeneous plastic deformation. In agreement with the conventional definition of the yield point for copper fully plastic behavior starded at permanent strains close to 0.005. The strain-hardening coefficient was very low at the early stage of plastic flow (“easy glide”), increasing progressively until values on the order of 0.13 to 0.14 were reached at maximum load. A this point, the appearance of unequally spaced fringes signaled the beginning of inhomogeneous deformation. With ESPI, this occurrence may thus serve as a criterion to establish the forming limit of the material.     

‘Best-case’ noise performance of feedback interferometers, potential for micromachine applications

We present a theoretical analysis of the noise performance of phase measuring feedback interferometers. We first analyse the operation of this kind of instrument and note that under certain circumstances bistability can occur. The bistable region should be avoided if possible when using feedback interferometry for high-accuracy measurement with low-input powers, as it can give rise to very high-noise levels. We then go on to investigate the effects of shot noise (on the interferometer output signal) and thermal noise (in the feedback loop), and relate these to the phase measurement accuracy of the interferometer. A ‘best-case’ calculation indicates that phase noise of about 0.005λ is possible at input powers in the nanowatt region. In practice, we expect that noise levels will be higher than predicted (particularly at high-input powers) due to the effects of vibration and air turbulence.     

A semi-automatic method for measuring interferometry fringes: prototype design and first results

A device for automatically obtaining the information contained in holographic interferometry fringes is proposed. The method may be applied to any kind of interferometric fringes. Accuracy has been demonstrated by contrasting the results obtained with our prototype system and those with the single-beam speckle interferometry technique for the measurement of displacements in a plane. The results show good correlation between the two series of measurements.