**6. Conclusions**

In order to reduce the effect of speckle noise, the windowed digital holographic interferometry was proposed. In the method, the effect of number of windows, or window size on accuracy, spatial resolution and calculation time were examined. The results are that the number of windows increases, the accuracy becomes better at first because of speckle noise reduction and after that it becomes worse because of larger speckle size. The best accuracy is sub-nanometer when the number of windows is 1024 in our experiment.

Three-Dimensional Displacement and Strain Measurements

Interferometry, *Strain*, Vol. 44, No. 1, 49-56

Interferometry, *Strain* (2008) 44, 366–373.

3165. doi:10.1364/AO.37.006262

Springer, ISBN: 978-0-387-34362-4, US

No.16, pp. 1268-1270, ISSN 0146-9592

Verlag: Springer, US

Sons, ISBN 0471960772

Berlin.

by Windowed Phase-Shifting Digital Holographic Interferometry 51

Morimoto, Y., Matui, T., Fujigaki, M. and Kawagishi, N. (2007) Subnano-meter displacement

Morimoto, Y., Matui, T., Fujigaki, M. and Matsui, A., (2008a). Three-dimensional

Morimoto, Y. Matui, T, Fujigaki, M. & Kawagishi, N., (2008b) Effects of Window Size on

Morimoto, Y. Matui, T, & Fujigaki, M. (2008c), Application of Three-Dimensional

Switzerland, doi: 10. 4028, http://www.scientific.net/AMR.47-50.1262 Okazawa, S., Fujigaki, M., Morimoto, Y. & Matui, T., (2006) Simultaneous Measurement of

Pedrini G., Fröning P., Fessler H., & Tiziani H.J. (1998). In-Line Digital Holographic

Pryputniewicz, R. J., (2008), Chap. 24 Holography, In: *Springer Handbook of Experimental Solid* 

Ranson, W. F., Sutton, M. A. & Peters, W. H. (1993). Chap. 8 Holographic and laser speckle

Schnars, U. & Ju¨ptner, W. (2005) *Digital Holography*. Springer, ISBN: 978-3-540-21934-7,

Sharpe, W. N. Jr., (Ed.), (2008), *Springer Handbook of Experimental Solid Mechanics*, Verlag:

Shiotani, K., Fujigaki, M., Matui, T. and Morimoto, Y., (2008) Strain Measurement Method

Yamaguchi, I. & Zhang, T. (1997), Phase-shifting digital holography, *Optics Letters*, Vol. 22,

10.4028/www.scientific.net/AMM.3-4.223, August, 2006

(Ed.), pp. 365-405, VCH Publishers, ISBN: 978-0-471-18864-3.

Sensors and Instrumentation, Yasuhiro Takaya, Ed, Dec. 2005

interferometry,. *Opt. Eng*. Vol. 46, No. 2,, 025603. ISSN 0091-3286

meter displacement measurement, *Proc. of SPIE*, Vol. 6049: Optomechatronic

measurement by averaging of phase-difference in windowed digital holographic

Displacement Analysis by Windowed Phase-shifting Digital Holographic

Accuracy and Spatial Resolution in Windowed Phase-Shifting Digital Holographic

Displacement and Strain Distribution Measurement by Windowed Phase-Shifting Digital Holographic Interferometry, Alan K.T. Lau, J. Lu, Vijay K. Varadan, F.K. Chang, J.P. Tu and P.M. Lam (Eds), *Multi-functional Materials and Structures, Advanced Materials Research*, Vol.47-50, pp1262-1265, (2008) Trans Tech Publications,

Out-of-Plane and In-Plane Displacements by Phase-Shifting Digital Holographic Interferometry, *Applied Mechanics and Materials (Volumes 3 - 4), Advances in Experimental Mechanics IV*, J.M. Dulieu-Barton and S. Quinn (Eds.), pp. 223-228,

Interferometry. *Appl. Opt*., Vol. 37, No. 26, pp. 6262-6269, ISSN 1559-128X, 2155-

*Mechanics*, Sharpe, W. N. Jr., (Ed.), pp. 675-700, Springer, ISBN: 978-0-387-34362-4,

interferometry," In: *Handbook on Experimental Mechanics*, 2nd ed., A.S. Kobayashi,

for Tilted Planar Object by Phase-Shifting Digital Holography Combined with Grating Projection Method, *Journal of JSEM*, Vol. 8, Special Issue, pp. 108-113. Valery, P. S., Vladimir, S. P., Sergey, A. N., Vitaly, V.B., Igor, N. O. & Mikhail, M. B. (1996).

*Strain and Stress Analysis by Holographic and Speckle Interferometry*, John Wiley &

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