Research on simultaneous measurement of the phase and group indices and the thickness of transparent plates and the scattering medium by the low coherence interferometry

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The research has been made to demonstrated the practical low coherence interferometer system which can provide simultaneous measurement of the phase and group indices and the thickness of transparent plates and the scattering medium such as biological tissues. Major research results are described in the following.1. We proposed and demonstrated a novel technique for simultaneous 'measurement of the phase and group indices and the thickness of a measured object. The technique is based on the low coherence interferometry combined with precise translation stages. In the experiment using the object scanning method, the measurement accuracy of 0.2% or less was attained for nearly 1-mm thick transparent plates. To realize a stable and compact measurement system, the low coherence interferometer consisted of micro-optic components on a optical bench of 50 x 60cm^2.2. On the basis of our proposed method, the automatic measurement of n_p and t taking the chromatic dispersion of the sample into account and the measurement n_p, n_g and t using the specific sample holder were successfully achieved within three minutes.3. The measurement accuracy of <1% was achieved even when the sample is as thin as 20mum, because of compensation for the unbalance of the chromatic dispersion between the sample and reference arms in the interferometer and using the alternative scanning method.4. Moreover, our measurement system is applicable for accurate measurement of refractive index of the scattering medium such as biological tissues. When the stage resolution is 1mum, the measurement accuracy of 1% or less is guaranteed for the sample thickness t more than 100mum. Simultaneous measurement of n and t were successfully achieved for a human nail, tooth, chicken tissue and a crustacean which has multiple layers.