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arXiv · 2108.13186

Ultra-precise determination of thicknesses and refractive indices of optically thick dispersive materials by dual-comb spectroscopy

Kana A. Sumihara·Sho Okubo·Makoto Okano·Hajime Inaba·Shinichi Watanabe
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Abstract

Precise measurements of the geometrical thickness of a sample and its refractive index are important for materials science, engineering, and medical diagnosis. Among the possible non-contact evaluation methods, optical interferometric techniques possess the potential of providing superior resolution. However, in the optical frequency region, the ambiguity in the absolute phase-shift makes it difficult to measure these parameters of optically thick dispersive materials with sufficient resolution. Here, we demonstrate that dual frequency-comb spectroscopy can be used to precisely determine the absolute sample-induced phase-shift by analyzing the data smoothness. This method enables simultaneous determination of the geometrical thickness and the refractive index of a planar sample with a precision of five and a half digits and an ultra-wide dynamic range. The thickness and the refractive index at 193.414 THz of a silicon wafer determined by this method are 0.52047(3) mm and 3.4756(3), respectively, without any prior knowledge of the refractive index.

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Kana A. Sumihara, Sho Okubo, Makoto Okano, Hajime Inaba, Shinichi Watanabe. 2021-08-30. Ultra-precise determination of thicknesses and refractive indices of optically thick dispersive materials by dual-comb spectroscopy. https://doi.org/10.1364/oe.445134

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