Prism-pair interferometry by homodyne interferometers with a common light source for high-accuracy measurement of the absolute refractive index of glasses
Yasuaki Hori, Akiko Hirai, and Kaoru Minoshima, "Prism-pair interferometry by homodyne interferometers with a common light source for high-accuracy measurement of the absolute refractive index of glasses," Appl. Opt. 50, 1190-1196 (2011)
A prism-pair interferometer comprising two homodyne interferometers with a common light source was developed for high-precision measurements of the refractive index of optical glasses with an uncertainty of the order of . The two interferometers measure changes in the optical path length in the glass sample and in air, respectively. Uncertainties in the absolute wavelength of the common light source are cancelled out by calculating a ratio between the results from the interferometers. Uncertainties in phase measurement are suppressed by a quadrature detection system. The combined standard uncertainty of the developed system is evaluated as .
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λ, wavelength of interferometer 1 and 2 (); , refractive index of sample prism; , refractive index of matching liquid; , apex angle of sample prism (Fig. 1); , offset between measurement passes of the two interferometers; , temperature coefficient of refractive index of air; , pressure coefficient of the refractive index of air; , humidity coefficient of the refractive index of air; , refractive index dispersion of sample prism at wavelength of ; , temperature coefficient of the refractive index of the sample prism.
Included in repeatability but not counted in the combined standard uncertainty or expanded uncertainty.
The uncertainty in the refractive index measurement , which is caused by the uncertainty of alignment of the perpendicularity is shown as ; is split into and for descriptive purposes.