**8. References**


However, the accuracy is better than the conventional averaging method with 11 by 11 pixels. The spatial resolution becomes worse when the number of windows becomes larger, that is, the window size becomes smaller. If the number of windows is constant, the accuracy and spatial resolution is better when the window size becomes larger. The calculation time increases according to the number of windows. In practice, it is useful when the number of windows is 16, 64 or 256 in our experiment. Three holographic systems were

A part of this study was supported by a grant aided project for creation of new regional industry of Kansai Bureau of Economy Trade and Industry. The authors also appreciate the support by Mr. Kita, Mr. Okazawa, Mr. Kawagishi, Mr. Kido and Mr. Shiotani, Graduate School of Systems Engineering, Wakayama University, and Mr. Kitagawa and Mr. Nakatani

Fujigaki, M., Matui, T., Morimoto, Y., Kita, T., Nakatani, M. & Kitagawa, A., (2005)

*Mechanics of Time Dependent Materials (MTDM05)*, pp. 160-163. Sep. 2005 Fujigaki, M., Kita, T., Okazawa, S., Matui, T. & Morimoto, Y. (2006) Calibration method with

Hayashi, T., Ugo, R. & Morimoto, Y. (1986). Experimental observation of stress waves

Kolenovic, E., Osten, W., Klattenhoff, R., Lai, S., Von Kopylow, C. and Ju¨ptner, W. (2003)

Appl. Opt. 42, pp. 5167–5172 ,ISSN 0003-6935, doi:10.1364/AO.42.005167 Morimoto, Y., Nomura, T., Fujigaki, M & Takahashi, I., (2004). "Reduction of speckle noise

Morimoto, Y., Nomura, T., Fujigaki, M., Yoneyama, S. and Takahashi, I. (2005a) Deformation

Morimoto, Y., Matui, T.,. Fujigaki, M & Kawagishi, N., (2005b) Accurate displacement

Morimoto, Y., Matui, T., Fujigaki, M. & Kawagishi, N. (2005c), Effect of weight in averaging

65–70, ISSN: 0014-4851, DOI: 10.1007/BF02428991

Portland, Oregon, USA, June 2005, pp. 7-9,.

Development of Real-Time Displacement Measurement System Using Phase-Shifting Digital Holography, *Proceedings of the 5th International Conference on* 

reference plane for phase-shifting digital holographic interferometry using spherical wave. *Int. Symp. Adv. Fluid/Sol. Sci. Technol. Exp. Mech., Sapporo, Japan,* pp.

propagating in laminated composites, *Experimental Mechanics*, Vol. 26, No. 2, pp.

Miniaturized digital holography sensor for distal three-dimensional endoscopy.

effect by divided holograms in phase-shifting digital holography", *Proc. of 12th Inter. Conf. on Experimental Mechanics* (CD-ROM), Politecnico di Bari, Italy, 29

measurement by phase-shifting digital holography. *Exp. Mech*. Vol. 45, No. 1, pp.

measurement by windowed holograms in digital holographic interferometry, *Proc. of 2005 SEM Annual Conference & Exposition on Experimental Mechanics* (CD-ROM),

of phases on accuracy in windowed digital holographic interferometry for pico-

developed and applied to measure 3D displacement and strain distributions.

**7. Acknowledgment** 

of Hitachi Zosen Corporation.

**8. References** 

11–14.

169-174, ISSN 1741-2765

August-2 Sept..

meter displacement measurement, *Proc. of SPIE*, Vol. 6049: Optomechatronic Sensors and Instrumentation, Yasuhiro Takaya, Ed, Dec. 2005


**0**

**3**

Atsushi Wada

*Japan*

*National Defense Academy*

**Multiple-Wavelength Holographic Interferometry**

Two-wavelength holographic interferometry is an effective technique to generate a contour map of a diffusely reflecting surface (Friesem & Levy (1976); Heflinger & Wuerker (1969); Hildebrand & Haines (1967); Yonemura (1985)). In this technique, two holograms are recorded with two wavelengths. An interference fringe pattern is generated by superposing

In digital holography, a hologram is recorded by an image sensor and saved into a computer. An object image can be reconstructed by numerical calculation. Several reconstruction methods were reported. Some of these have adjustablity of position and scale of a reconstruction image (Yu & Kim (2006); Zhang et al. (2004)). An object phase distribution can be obtained by the numerical reconstruction of digital holograms. Therefore, two-wavelength digital holographic interferometry makes it possible to generate a contour map by numerical extraction of a phase difference between two reconstructed images (Gass et al. (2003); Parshall & Kim (2006); Wagner et al. (2000; 1999); Yamaguchi (2001); Yamaguchi et al. (2006)). A phase difference extracted from reconstructed object images is wrapped into a half-open interval (−*π*,*π*]. If a measured object height was large with respect to a synthetic wavelength, 2*π* ambiguities of the phase difference should be eliminated for retrieving the object profile. Common phase unwrapping algorithms (Asundi & Wensen (1998); Servin et al. (1998)) which use phase information of neighbor pixels can be applied when an object structure has no discontinuity. However the algorithms can not work correctly for an object profile having

An object profile with discontinuous structure can be measured by two-wavelength interferometry with a sufficiently large synthetic wavelength. For example, two-wavelength holographic interferometry with a ruby laser and a synthetic wavelength of ∼ 2 cm was reported (Heflinger & Wuerker (1969); Pedrini et al. (1999)). Nevertheless the measurement error tends to be amplified linearly with an increase in the synthetic wavelength since most of the error sources are the product of the synthetic wavelength and an error of the extracted

A technique which eliminates 2*π* ambiguities by using a phase difference with a large synthetic wavelength was reported (Cheng & Wyant (1985); de Groot (1991); Wagner et al. (2000)). This technique makes it possible to measure a large step-height with high depth resolution. Wagner *et. al.* reported multiple-wavelength holographic interferometry using a dye laser. They combined three phase differences with synthetic wavelengths of 3.04 mm,

**1. Introduction**

two object images reconstructed from the holograms.

isolated region surrounded by discontinuous step.

phase difference (Cheng & Wyant (1984)).

**with Tunable Laser Diodes**

