Simultaneous measurement of refractive index and thickness by combining low-coherence interferometry and confocal optics.
We propose and demonstrate novel methods that enable simultaneous measurements of the phase index, the group index, and the geometrical thickness of an optically transparent object by combining optical low-coherence interferometer and confocal optics. The low-coherence interferometer gives information relating the group index with the thickness, while the confocal optics allows access to the phase index related with the thickness of the sample. To relate these, two novel methods were devised. In the first method, the dispersion-induced broadening of the low-coherence envelop signal was utilized, and in the second method the frequency derivative of the phase index was directly obtained by taking the confocal measurements at several wavelengths. The measurements were made with eight different samples; B270, CaF2, two of BK7, two of fused silica, cover glass, and cigarette cover film. The average measurement errors of the first and the second methods were 0.123% and 0.061% in the geometrical thickness, 0.133% and 0.066% in the phase index, and 0.106% and 0.057% in the group index, respectively.
Department of Information and Communications, Gwangju Institute of Science and Technology, 1 Oryong-dong, Buk-Gu, Gwangju, 500-712, Korea.
Seokhan
S
Kim
Jihoon
J
Na
Myoung Jin
MJ
Kim
Byeong Ha
BH
Lee
D003198:Computer Simulation; D017076:Computer-Aided Design; D004867:Equipment Design; D019544:Equipment Failure Analysis; D007368:Interferometry / Q000295:instrumentation* / Q000379:methods; D007909:Lenses; D008422:Materials Testing / Q000295:instrumentation* / Q000379:methods; D018613:Microscopy, Confocal / Q000295:instrumentation* / Q000379:methods; D008962:Models, Theoretical; D012031:Refractometry / Q000295:instrumentation* / Q000379:methods