METHOD AND DEVICE FOR MEASURING AIR REFRACTIVE INDEX BASED ON LASER SYNTHETIC WAVELENGTH INTERFERENCE

摘要

A method and a device for measuring air refractive index based on laser synthetic wavelength interference are disclosed. The laser synthetic wavelength interferometer is composed of a double frequency laser, a spectroscope, two polarization spectroscopes and two pyramid prisms. The quartz vacuum cavity is located in the measuring optical paths and is parallel with the direction of ray propagation. During the measurement, the air is conveyed to the quartz vacuum cavity until equaling the outside environment. Then, the change of the air refractive index in the cavity can cause the change of the interference signal of the wavelength ?2. The integral change number N of interference fringes of the wavelength ?2 is directly detected by photoelectric detector. Then, the pyramid prisms of the interferometer is moved, so as to make the phase difference of the interferential signal of wavelength ?1 and ?2 equal to the original phase difference before conveying the air to the quartz vacuum cavity. Based on the subdivisional principle of the laser synthetic wavelength interference fringes, the decimal fraction e of change part of interference fringes of the wavelength ?2 is detected. Air refractive index n is computed according to the length L of vacuum cavity, the integer N of interference fringes and the decimal fraction e. The invention has the measurement accuracy of over 10-9 and strong environment interference resisting capability.