Humidity Correction of Air Refractive Index Based on a Phase Shift Interferometry with Three Stabilized Laser Wavelengths

Revised Edlen's equations by G. Boensch and E. Potulski are mostly used to calculate air refractive index at present. Since the correction of the humidity in the equations is performed in a narrow temperature range around 20°C and the light frequency of the four wavelengths ¹¹⁴Cd lamp are not stabile, their applications have been limited in present optical precision measurement. To solve these problems, a refractive index measurement system was presented based on phase step interferometry. First, the configuration and principle of the optical system were introduced, which consisted of a phase step interferometer with three stabilized laser sources and an assistant angle sensitive interference optical path. Then the experimental and computing processes were induced. Finally, the experiments were carried out at different temperature. The corrected coefficients of the humidity on air refractive index were measured and corresponding revised equation was acquired. The comparison results indicate that the correction accuracy with the presented equation is better than that by G. Boensch. Moreover, the applicable temperature range extends to 14.6~24.0℃.