[OPTICAL REVIEW Vol. 4, No. 4 (1997) 507-515]

Simultaneous Measurement of Refractive Index and Thickness of Transparent Plates by Low Coherence Interferometry

Masato OHMI,1 Takehisa SHIRAISHI,2 Hideyuki TAJIRI2 and Masamitsu HARUNA1,2

1School and Allied Health Sciences, Faculty of Medicine, Osaka University, 1-7, Yamadaoka, Suita, Osaka 565 Japan, 2Course of Electronic Engineering, Graduate School of Engineering, Osaka University, 2-1, Yamadaoka, Suita, Osaka, 565 Japan

(Received December 16, 1996; Accepted April 24, 1997)

>We demonstrate a novel low coherence Michelson interferometer which can provide simultaneous measurement of the refractive index and thickness of transparent plates used as a measured object. Unlike the existing low coherence interferometers reported so far, either an object or a focusing lens aligned on the signal arm is scanned repeatedly by a precise translation stage in synchronization with movement of a reflection mirror on the reference arm. The so-called object or lens scanning method gives us two measured quantities a movement distance of the stage between two light focusing states on the front and rear planes of an object and the corresponding optical path difference. These two measured quantities, result in desirable values of the index and thickness of the object with a short calculation. The measurement accuracy of ≤0.1% is expected for a thickness of more than 1 mm. In the experiment using the object scanning method, the accuracy of 0.3% or less was successfully attained for nearly 1-mm thick plates of fused quartz, sapphire, LiTaO3 and slide glass.

Key words : low coherence light source, interferometry, simultaneous measurement of index and thickness, opto-electronics, precise mechanics