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Digital holographic profilometry using multiwavelength from two laser diodes is applied to the measurement of the inner surface of a straight copper pipe and the detection of artificial defects such as holes, rust, and scratches made on the inner wall. To obtain the inner surface profile, a cone-shaped mirror (CSM) attached to a metal rod having two acrylic spacers is inserted into the pipe and illuminated by the collimated laser beam from the other open end of the pipe. The inspection of the pipe has been performed by shifting the CSM stepwise along the pipe axis. The new algorithm in which a positional misalignment of the CSM can be directly obtained from the experimental height profile can reduce the load for calculation of correcting the distorted experimental height profile. The pipe inspection has been done using the developed images of both the intensity and height profile for the inner wall of the pipe. [ABSTRACT FROM AUTHOR]

A combination method to study the drying process of paints, based on digital holography and gravimetric measurement, is proposed. The proposed method allows taking holographic measurement in a simultaneous way to compare the results obtained by the reconstructed image changes with gravimetric data. By directly comparing a phase change in the reconstructed images of a paint surface and weight change of the paint film, it is found that a stationary state of the paint surface detected by the phase change occurs in the last stage of solvent evaporation and corresponds to a dry-hard of the paint film. The proposed technique can also analyze dryness of clear coat having no scattering particle using the phase change. It is shown that the present technique can allow us to further investigate not only a film formation of clear coat but also an estimation of specific gravity of solvents by comparing directly the phase change with weight loss due to solvent evaporation in the simultaneous measurement. [ABSTRACT FROM AUTHOR]

An optical voltage sensor is presented which can be used for the measurement of dc voltage by use of a Pockets crystal associated with a pulse-controlled electrooptic quarter waveplate. The measurand dc voltage signal is converted into the amplitude of an ac pulse-modulated voltage-sensing signal. Therefore, the output sensing signal is immune to electromagnetic interference owing to the applications of pulse modulation and lock-in amplifying techniques. In addition, the voltage-sensing signal is obtained from a single light path and free from light intensity fluctuations. The dc voltage of ±0.4 to ±180 V has been measured with 1.8% nonlinear error. [ABSTRACT FROM AUTHOR]

A new algorithm for fringe phase analysis is proposed for shape and deformation measurement of diffusely reflecting surfaces by digital holography. It derives the phase of the averaged conjugate product of complex amplitudes before and after wavelength change or object deformation, corresponding to the complex coherence factor, and is consistent with a theory on fringe formation in holographic interferometry. By experiments and computer simulations, it is demonstrated that the algorithm is much more immune to speckle noise in phase analysis and unwrapping than conventional methods. [ABSTRACT FROM AUTHOR]

Digital holography is applied to analyze the spatial distribution of the polarization state of light transmitted through anisotropic objects by successive hologram recording using polarization switching of the reference wave by an optical fiber Faraday rotator. For a preliminary object to confirm the principle of polarization analysis, a quarter wave plate (QWP) is used, and the distribution of the polarization ellipse over the object surface is analyzed for various azimuths of the QWP. By inserting a polarizer into a part of the object wave after the object as a reference area, a phase drift of the reference waves caused by polarization switching and/or environmental disturbances can be evaluated and compensated for by using the reference area. The principal axis and ellipticity are calculated and compared with their theoretical values. A good agreement between the experimental and theoretical values is observed. For an application, a photoelastic effect induced in a stressed PMMA specimen is also investigated. [ABSTRACT FROM AUTHOR]