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18 February 2008 Dispersion-assisted measurement of the refractive index and thickness by hybrid interferometer
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We propose and demonstrate two new techniques based on the hybrid-interferometer, composed of optical low-coherence interferometer and confocal optics to simultaneously measure the phase index (np), group index (ng) and geometrical thickness (t) of optically transparent materials. In the first method, we utilize the interference signal measured with several laser sources having different center wavelength and calculate the square of dispersion parameter τc2) of a glass plate from the interference signals. By analyzing the dispersion effect of interference signals, we can successfully separate the three parameters. In the second method, we approximate the derivative term of phase index in the definition of group index, by using the confocal signals measured with the laser sources having different center wavelength. From this approximation, we can also separate the parameters. The average measurement errors of first and second method are ~0.123 %, ~0.061 % in geometrical thickness, ~0.133 %, ~0.066 % in phase index, and ~0.106 %, ~0.057 % in group index, respectively, for eight different samples which are B270, CaF2, two of BK7, two of fused silica, cover glass and cigarette cover film. We are currently attempting to improve the accuracy and this technique will be extended to index measurement for biomedical tissues.
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Seokhan Kim, Jihoon Na, Myoung Jin Kim, and Byeong Ha Lee "Dispersion-assisted measurement of the refractive index and thickness by hybrid interferometer", Proc. SPIE 6847, Coherence Domain Optical Methods and Optical Coherence Tomography in Biomedicine XII, 68470X (18 February 2008);

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