Suazou Nakadate

Bio: Suazou Nakadate is an academic researcher from Tokyo Institute of Technology. The author has contributed to research in topics: Holographic interferometry & Interference (wave propagation). The author has an hindex of 1, co-authored 1 publications receiving 33 citations.

Hybrid Holographic Interferometer For Measuring Three-Dimensional Deformations

Abstract: A method for automatically measuring the three-dimensional (3-D) deformations of a diffuse surface is studied, using a real-time holographic interferometer and a television-computer system. The object surface is illuminated from three different directions. The scattered waves are recorded on a thermoplastic hologram. Real-time holographic interference patterns are observed through the hologram in a fixed direction by sequentially applying the three illuminating beams. The three fringe patterns are put into the computer using a television (TV) camera. The relative fringe order numbers are determined over the whole surface. Calculations for obtaining 3-D deformation distributions are performed, and the results are displayed on a cathode-ray tube (CRT) monitor.

IV Advanced Evaluation Techniques in Interferometry

Abstract: Publisher Summary This chapter describes the advanced evaluation techniques in interferometry The chapter discusses the methods that rely on the adjustment of a fringe pattern The chapter examines the historically older interpolation methods where the phase information is extracted from the positions of the extrema The chapter also discusses more general methods that deliver the phase in a more continuous form A comparison of the different methods for phase evaluations necessitates a consideration of the error sources and limitations These error sources for the case of phase sampling interferometry (PSI) have been discussed The error causes are classified into statistical errors (measuring errors that can be diminished in their influence by averaging) and systematic errors (errors that cannot be quenched) The interferometers used in the assessment of test data are rather complex, thus, there is some necessity for calibration The interferometer aberrations, even with ideal test samples, are caused by deviations of optical elements and to also by the state of adjustment The chapter identifies the types of error sources—namely, environmental errors, errors that are dependent on the method, and errors typically encountered in interferometry

Fringe scanning speckle-pattern interferometry.

Abstract: Digital speckle-pattern interferometry systems for automatic measurement of deformations of a diffuse object are presented, which are based on a fringe scanning method with phase-shifted speckle interferograms. A digital speckle pattern before deformation of an object is recorded in the mass storage device of a computer facility. After deformation, four digital speckle patterns are recorded as changing the phase of reference light such as 0, π/2, π, and 3π/2, respectively. Four speckle interferograms, whose phases are shifted by 0, π/2, π, and 3π/2, are generated by calculating the square of the differences between speckle patterns before and after deformation. These interferograms are low-pass filtered to reduce speckle noise. The calculation of the arctangent with four phase-shifted speckle interferograms gives the optical path difference which is proportional to the deformation. A correction of the discontinuity of the calculated phase gives the numerical data of the deformation in the whole object area. Some experimental results for the measurement of out-of-plane, in-plane, and 3-D deformations are presented.

Real-time holographic interferometry: a microcomputer system for the measurement of vector displacements.

Abstract: A system is described which uses a diode array TV camera to view the real-time fringes and digital electronics to measure and store the irradiance levels at a 100 × 100 array of points. A microcomputer calculates the phase at each point from the irradiance values obtained from three successive scans of the array made with the phase of the reference beam shifted in steps of 120° by means of a mirror mounted on a piezoelectric translator. The optical system permits four holograms to be recorded in quick succession, using a photothermoplastic camera, with the object illuminated from four different directions. Phase data from these holograms are processed in a microcomputer to determine the components of the vector displacement at each of these points; these figures can then be transferred to a fast computer for further processing to evaluate the stress distribution.

Moiré profilometry using liquid crystals for projection and demodulation.

Abstract: A projection moire profilometer is presented in which both projection and optical demodulation are realized with liquid crystal light modulators. The computer generated grids, realized on thin film transistor matrices, allow phase-stepping and discrete grid averaging without the need for any mechanically moving component. Spatial line pitch and phase steps can thus be readily adjusted to suit the measurement precision and object geometry. The device is able to perform topographic measurements with a height resolution of 15 microm on every pixel of the recording device.

V Fringe Formations in Deformation and Vibration Measurements Using Laser Light

Abstract: Publisher Summary This chapter focuses fringe formations in deformation and vibration measurements using laser light. The chapter discusses a survey on the formation of the fringe patterns observed in these methods. The chapter helps in deriving dependences of their shape and visibility on object deformation parameters and optical systems by starting from the correlation properties of the light scattered from diffuse objects, and discuss the mutual relationships and features of each method by putting physical interpretations on derived mathematical relations. In holographic interferometry and speckle interferometry, the fringe shape represents the distribution of the phase change of the scattered light caused by object deformation, while the fringe visibility depends on the overlap of the corresponding speckle pair, therefore, on speckle displacement and speckle size. In speckle photography, on the other hand, the fringe shape represents the speckle displacement, while the fringe visibility is affected by the speckle decorrelation accompanying the displacement. In addition the relations derived in the present chapter would deliver a quantitative basis for selecting an adequate method of measurement and the optimum manner of signal processing in these modem interferometric techniques.