Measurement of the changes in air refractive index and distance by means of a two-color interferometer

Abstract

<p>We discuss the measurements of the changes in air refractive indices and geometrical distances by means of a two-color phase-modulated fringe-counting interferometer. We analytically classified the optical path lengths for IR and visible light into the changes in the air refractive index and the distance by using a dispersion formula for air. The interferometer was tested over a 235-m path in the testing tunnel of the National Research Laboratory of Metrology, which has a sensor system for measuring air conditions.</p> <p>The refractive-index change by the two-color interferometer agreed with the value calculated by the air conditions within an accuracy of 0.15 ppm.</p>

Comparison of two-color methods based on wavelength and adjacent pulse repetition interval length

“…Based on the previous studies [5,6,7,10,13,14,27,28], the following characteristics for the wavelength-based two-color method are well known.…”

Correction of refraction index based on adjacent pulse repetition interval lengths

“…Since the early stage of the two-color method [3], many contributions have been made to correction of the atmospheric index of refraction [4][5][6][7][8][9][10][11][12][13][14][15][16][17].…”