High-accuracy correction of air refractive index by using two-color heterodyne interferometry of optical frequency combs

• Published in: Measurement science & technology Vol. 24; no. 1; pp. 15203 - 15211
• Main Authors: Wu, Guanhao, Arai, Kaoru, Takahashi, Mayumi, Inaba, Hajime, Minoshima, Kaoru
• Format: Journal Article
• Language: English
• Published: IOP Publishing 01.01.2013
• Subjects: air refractive index; heterodyne interferometry; optical frequency comb; two-color
• ISSN: 0957-0233; 1361-6501
• DOI: 10.1088/0957-0233/24/1/015203

High-accuracy two-color heterodyne interferometry based on fundamental and second harmonic of frequency combs for air refractive index correction is developed. A monitor interferometer as well as a probe interferometer is constructed to compensate the phase noises and drifts, which are caused by introducing the acousto-optic modulators for heterodyne interferometer, to realize high-accuracy measurement of optical distance. A relative stability of 10−10 to the total length for 500 s is achieved in the measurement of an optical path length difference between two wavelengths. In long-term measurements, the interferometric measurement results and the calculations from empirical equation of air refractive indices are in good agreement with a standard deviation of 4.1 × 10−10 throughout the 10 h period. By applying the two-color method, high-accuracy correction of air refractive index with an uncertainty of 8.9 × 10−8 is achieved during 10 h continuous measurements while the total refractive index changes with a range of 2.0 × 10−6.