Research

In long-distance ranging, the air refractive index is the main factor affecting accuracy. The dual-wavelength method is an effective method for correcting the air refractive index in long-distance measurements, but it requires high precision for optical path length. This research group, in collaboration with Professor Minoshima's group at the University of Electro-Communications in Japan, jointly studied the dual-wavelength air refractive index based on optical frequency comb heterodyne interferometry. This method uses an optical frequency comb as the light source, greatly improving frequency stability; meanwhile, the heterodyneometry technique overcomes the disadvantage of zero-beat interferometry precision being affected by intensity noise, significantly improving the final optical path length measurement accuracy. In the experiment, a-harmonic generation crystal was used to obtain the dual wavelengths, simplifying the light source device; a dual-reference arm setup was adopted to compensate for the drift of acsto-optic and electrical instruments. Ultimately, at a distance of 61 m, an air refractive index correction accuracy of 1.4×10^- was achieved.