Automatic real-time compensation of vacant band error based on monitor the laser heterodyne interferometry timely

In order to compensate the vacant band error automatically and timely in the real-time measurement, a method based on measuring the value of the refractive index and length of the vacant band timely is proposed. The method uses the laser ranger, polarization film and polarization rotator to buildup the metrical apparatus and measure the length value of vacant band, uses the refractive index metrical apparatus to get the value of the refractive index, then according to the 'end correction method' the vacant band error can be compensated. The experiment result shows that the system can reduce the zero deviation from 300 nm to 30 nm based on the HP5528 heterodyne interferometry system, when the refractive index floats 2.7 × 10^-6 and the length of the vacant band is 100 mm.