Two-Wavelength Laser Interferometer System Which Reduces the Uncertainty Caused by the Fluctuation of the Refractive Index of Air
Kaoru Miyata, Hidekazu Oozeki, Hideyuki Nakagawa,
Hiroki Masuda, and Hisayoshi Sakai
Mitutoyo Corporation, 430-1 Kamiyokoba, Tsukuba-shi, Ibaraki-ken 305-0854, Japan
Laser interferometers are widely used to measure highly sensitive length and displacement, e.g., in which refractive index fluctuations of air adversely affect measurement accuracy. To compensate for these effects, the two-wavelength interferometer studied has not yet proved practical in industrial use. We studied the interferometer’s performance and practicality, using uncertainty analysis to extract its features. Based on our results, we developed a two-wavelengthMichelson interferometer with wavelengths of 1064 nm and 532 nm. It was calibrated and evaluated using a highprecision laser interferometer whose optical path was in a vacuum. Results confirmed measurement accuracy of 100 nm/50 mm (k=2) under unstable air conditions – superior to a traditional laser interferometer.
-  P. Bender and J. Owens, “Correction of optical distance measurements for the fluctuating atmospheric index of refraction,” J. Geophys. Res., Vol.70, pp. 2461-2462, 1965.
-  K. B. Earnshaw and E. N. Hernandez, “Two-laser optical distancemeasuring instrument that corrects for the atmospheric index of refraction,” Appl. Opt., 11, pp. 749-754, 1972.
-  A. Ishida, “Two-Wavelength Displacement-Measurihg Interferometer Using Second Harmonic Light to Eliminate Air-Turbulence-Induced Errors,” J. Appl. Phy. Letter. 28-3, pp. L473-475, 1989.
-  L. Zeng, K. Seta, H. Matsumoto, and S. Iwasaki, “Length Measurement by a Two-color Interferometer that uses Two CloseWavelengths to Reduce Error caused by Air Turbulence,” Measurement Science and Technology, 10-7, pp. 587-591, 1999.
-  P. E. Ciddor, “Refractive index of air, new equation for the visible and near infrared,” Appl. Opt., 35, pp. 1566-1573, 1996.