King Ung HII^1,2* 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

^*E-mail address: khii@swinburne.edu.my