Jing-Heng CHEN^*, Kun-Huang CHEN¹, Chien-Yuan HAN², Chun-Wei WU, and Nung-Yu WU

Department of Photonics, Feng Chia University, 100 Wenhwa Road, Seatwen, Taichung 40724, Taiwan, R.O.C.
¹Department of Electrical Engineering, Feng Chia University, 100 Wenhwa Road, Seatwen, Taichung 40724, Taiwan, R.O.C.
²Department of Electro-Optical Engineering, National United University, 1 Lienda, Miaoli 36003, Taiwan, R.O.C.

(Received July 8, 2008; Revised April 1, 2009; Accepted April 14, 2009)

In this study a modified method of Talbot interferometry is developed to evaluate the curvature of an object. The tilt angle of moiré fringe formed by two gratings is related to the wavelength, the grating periods, the angle between these two gratings, and the object curvature. Therefore, substituting the known experimental parameters into a special derived equation the object curvature can be evaluated. In order to show the validity of this method, stainless steel balls with curvatures of 1.326 and 1.261 mm^-1 were measured. The measurement resolution of curvature was about 3.729× 10^-3 mm^-1. It is shown that this method is suitable for both transmission and opaque objects with high accuracy.

Key words: moiré fringes, Talbot interferometry, curvature, gratings, reflection-type

^*E-mail address: jhchen@fcu.edu.tw