A Common-Path Compensation Method For Laser Beam Drift And Its Experimental Study

Laser bean drift is a major factor that affects the accuracy of straightness measurements in the laser collimation. There are three main factors that cause the laser beam drift. That is, light beam drift produced by the laser itself and by the mechanical slow position changes in the measurement head, the light bend by the index gradient in the propagating air, and stochastic turbulence. The laser beam drift can be divided into two kinds: parallel drift and angular drift. The laser angular drift will cause much more errors in straightness measurement, especially for long distance straightness measurements, as the measurement error produced by the laser angular drift is proportional to the collimation distance. So the laser angular drift must be controlled to reduce the measurement error in long distance straightness measurement.In order to reduce the influence produced by the laser beam angular drift in the laser collimation, a simple common-path compensation method was put forward in the thesis. The angle of the laser angular drift can be measured in-time, and the measurement error produced by the laser angular drift can be compensated. This common-path method can be used in any collimation measurement such as straightness and angular measurements. The compensation principle and the system design were discussed, and different experiments were carried out. The experimental results showed that the measurement error induced by laser angular drift in the straightness can be reduced by 30%～73.5% in the measurement range from two to eight meters.