Regular Paper

[OPTICAL REVIEW Vol. 21, No. 5 (2014) 705-708]
© 2014 The Japan Society of Applied Physics

Simultaneous Measurement of Refractive Index and Thickness with a Convergent Beam

King Ung HII1,2* and Kuan Hiang KWEK1

1Department of Physics, Faculty of Science, University of Malaya, 50603 Kuala Lumpur, Malaysia
2Faculty of Engineering, Computing and Science, Swinburne University of Technology, Sarawak Campus, 93350 Kuching, Malaysia

(Received March 31, 2014; Revised July 2, 2014; Accepted July 2, 2014)

A new approach to the simultaneous measurement of refractive index and thickness based on the focus shifts of a convergent beam intercepted by a test plate is proposed. By using ray optics, a defined focus shift can be derived as a function of the refractive index and thickness as well as the angular position of the test plate with respect to the optical axis. From a pair of focus shifts obtained at two different angular positions, it is shown that the desired measurands can be simultaneously determined without prior knowledge of either parameter. A simulation result for the proposed concept based on graphically solving the equations of their respective focus shifts is presented.

Key words: optical measurements and metrology, refractive index, thickness, optical materials, geometrical optics

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