A robust air refractometer for accurate compensation of the refractive index of air in everyday use.

The definition of the meter is based on the speed of light in a vacuum; however, most dimensional measurements, when performed using laser interferometry, are performed in air. A velocity of light compensation needs to be applied to the velocity of the laser light for accurate measurements of the speed of light to be approximated in a vacuum. Most practices use a weather-station method, whereby the ambient conditions are measured. Thereafter, the modified Edlen’s equation is used, and corrections are calculated for the wavelength of the laser. The theoretical calculation is, however, only accurate to 3*10−8 without taking into account the accuracy of the sensors. Thus, this work focuses on investigations into the velocity of light compensations, both to improve upon the accuracy of the Edlen equation method in everyday use, and to verify the accuracy of the current weather-station systems in use through comparison with the refractometer. A refractometer that allows for velocity of light compensation measurements was developed, tested, and verified. The system was designed to be simple and cost-effective for use in everyday dimensional measurements, but with high accuracy. Achieved results show that although simple in design, the refractometer is accurate to at least 1*10−8, which meets our initial condition for design.