Abstract
In spectral domain interferometry, the interference signal generated by directly reflected waves from the two surfaces of a sample plate under test is greatly enhanced by the blockage of those light waves reflected by the two arm mirrors in the Michelson interferometer. This sample surface-reflected interference signal, being the optical path length of the plate, is therefore identifiable directly from the Fourier-transformed interference spectrum. Consequently, the group refractive index and physical thickness of the plate can be obtained simultaneously without any prior information of them. Moreover, subsequent in situ angular scanning on the interference spectra helps to retrieve the wavelength-dependent phase refractive index and first-order dispersion. The order of magnitude of the relative error for the group refractive index is 10(-4), while that for the phase refractive index and the physical thickness is 10(-3).
Highlights
Accurate measurements of the optical parameters, such as physical thickness and refractive index of optical plates, are important in research and practical applications [1,2]
We propose a simple method based on spectral domain (SD) low coherence interferometry (LCI) with an enhanced signal of optical path length (OPL), which is formed by the interference of the light waves collinearly reflected from the front and rear surfaces of sample plates under test, so that the OPL can be read out directly other than by subtracting of two relative peaks [7]
The second one is the value of ng · d, the OPL, which is usually obtainable from the interferences of light reflected from sample surfaces and the reference mirror [7,8,9]
Summary
Accurate measurements of the optical parameters, such as physical thickness and refractive index of optical plates, are important in research and practical applications [1,2]. The interferometric method, in general, measures the optical path length (OPL) in a sample [3], which is a coupled quantity of refractive index and physical thickness. Based on optical coherence tomography (OCT) or low coherence interferometry (LCI), Wang et al [4], Hirai and Matsumoto [5], and Cheng and Liu [6] measured the group refractive index and physical thickness of their samples in the time domain. Maruyama and co-workers [10,11] and Kim et al [12] measured an additional parameter, the phase refractive index, in the time domain
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