Absolute gas refractometer without gas-filling and pumping process benefiting from quasi-synthetic wavelength theory

TL;DR

This paper introduces an absolute gas refractometer that uses quasi-synthetic wavelength theory and a two-frequency interferometry setup, eliminating the need for gas filling or pumping, and achieves high precision in measuring gas refractive index.

Contribution

The paper presents a novel method combining quasi-synthetic wavelength theory with a two-frequency Jamin interferometer to measure gas refractive index without filling or pumping gas.

Findings

Uncertainty better than 1E-7

Dynamic range of 3.95E-4

Effective measurement of dry air and nitrogen at various pressures

Abstract

We present a method to measure the refractive index of gas at 633 nm absolutely, which does not need filling or pumping gas during the measurement. We develop a quasi-synthetic wavelength (QSW) theory by means of the configuration of two-frequency Jamin interferometry and vacuum tubes with specific lengths. With the aid of the QSW theory, we construct a gas refractometer and demonstrate its performance by the measurement of dry air and nitrogen gas at different pressures ranging from 80 kPa to 100 kPa. The results indicate that the refractometer has an uncertainty of better than 1E-7 and a dynamic range of 3.95E-4.